Merge #320

320: Sort at query time r=Kerollmops a=Kerollmops

Re-introduce the Sort at the query time (https://github.com/meilisearch/milli/issues/305)

Co-authored-by: Clément Renault <renault.cle@gmail.com>

benchmarks/benches/search_songs.rs

@@ -52,9 +52,9 @@ fn bench_songs(c: &mut criterion::Criterion) {
         milli::default_criteria().iter().map(|criteria| criteria.to_string()).collect();
     let default_criterion = default_criterion.iter().map(|s| s.as_str());
     let asc_default: Vec<&str> =
-        std::iter::once("asc(released-timestamp)").chain(default_criterion.clone()).collect();
+        std::iter::once("released-timestamp:asc").chain(default_criterion.clone()).collect();
     let desc_default: Vec<&str> =
-        std::iter::once("desc(released-timestamp)").chain(default_criterion.clone()).collect();
+        std::iter::once("released-timestamp:desc").chain(default_criterion.clone()).collect();
 
     let basic_with_quote: Vec<String> = BASE_CONF
         .queries
@@ -118,12 +118,12 @@ fn bench_songs(c: &mut criterion::Criterion) {
         },
         utils::Conf {
             group_name: "asc",
-            criterion: Some(&["asc(released-timestamp)"]),
+            criterion: Some(&["released-timestamp:desc"]),
             ..BASE_CONF
         },
         utils::Conf {
             group_name: "desc",
-            criterion: Some(&["desc(released-timestamp)"]),
+            criterion: Some(&["released-timestamp:desc"]),
             ..BASE_CONF
         },
 

http-ui/src/main.rs

@@ -1030,7 +1030,7 @@ mod tests {
             displayed_attributes: Setting::Set(vec!["name".to_string()]),
             searchable_attributes: Setting::Set(vec!["age".to_string()]),
             filterable_attributes: Setting::Set(hashset! { "age".to_string() }),
-            criteria: Setting::Set(vec!["asc(age)".to_string()]),
+            criteria: Setting::Set(vec!["age:asc".to_string()]),
             stop_words: Setting::Set(btreeset! { "and".to_string() }),
             synonyms: Setting::Set(hashmap! { "alex".to_string() => vec!["alexey".to_string()] }),
         };
@@ -1058,7 +1058,7 @@ mod tests {
                 Token::Str("criteria"),
                 Token::Some,
                 Token::Seq { len: Some(1) },
-                Token::Str("asc(age)"),
+                Token::Str("age:asc"),
                 Token::SeqEnd,
                 Token::Str("stopWords"),
                 Token::Some,

milli/Cargo.toml

@@ -25,7 +25,6 @@ obkv = "0.2.0"
 once_cell = "1.5.2"
 ordered-float = "2.1.1"
 rayon = "1.5.0"
-regex = "1.4.3"
 roaring = "0.6.6"
 serde = { version = "1.0.123", features = ["derive"] }
 serde_json = { version = "1.0.62", features = ["preserve_order"] }

milli/src/criterion.rs

@@ -1,15 +1,10 @@
 use std::fmt;
 use std::str::FromStr;
 
-use once_cell::sync::Lazy;
-use regex::Regex;
 use serde::{Deserialize, Serialize};
 
 use crate::error::{Error, UserError};
 
-static ASC_DESC_REGEX: Lazy<Regex> =
-    Lazy::new(|| Regex::new(r#"(asc|desc)\(([\w_-]+)\)"#).unwrap());
-
 #[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
 pub enum Criterion {
     /// Sorted by decreasing number of matched query terms.
@@ -17,10 +12,13 @@ pub enum Criterion {
     Words,
     /// Sorted by increasing number of typos.
     Typo,
+    /// Dynamically sort at query time the documents. None, one or multiple Asc/Desc sortable
+    /// attributes can be used in place of this criterion at query time.
+    Sort,
     /// Sorted by increasing distance between matched query terms.
     Proximity,
     /// Documents with quey words contained in more important
-    /// attributes are considred better.
+    /// attributes are considered better.
     Attribute,
     /// Sorted by the similarity of the matched words with the query words.
     Exactness,
@@ -43,29 +41,46 @@ impl Criterion {
 impl FromStr for Criterion {
     type Err = Error;
 
-    fn from_str(txt: &str) -> Result<Criterion, Self::Err> {
-        match txt {
+    fn from_str(text: &str) -> Result<Criterion, Self::Err> {
+        match text {
             "words" => Ok(Criterion::Words),
             "typo" => Ok(Criterion::Typo),
+            "sort" => Ok(Criterion::Sort),
             "proximity" => Ok(Criterion::Proximity),
             "attribute" => Ok(Criterion::Attribute),
             "exactness" => Ok(Criterion::Exactness),
-            text => {
-                let caps = ASC_DESC_REGEX
-                    .captures(text)
-                    .ok_or_else(|| UserError::InvalidCriterionName { name: text.to_string() })?;
-                let order = caps.get(1).unwrap().as_str();
-                let field_name = caps.get(2).unwrap().as_str();
-                match order {
-                    "asc" => Ok(Criterion::Asc(field_name.to_string())),
-                    "desc" => Ok(Criterion::Desc(field_name.to_string())),
-                    text => {
-                        return Err(
-                            UserError::InvalidCriterionName { name: text.to_string() }.into()
-                        )
+            text => match AscDesc::from_str(text) {
+                Ok(AscDesc::Asc(field)) => Ok(Criterion::Asc(field)),
+                Ok(AscDesc::Desc(field)) => Ok(Criterion::Desc(field)),
+                Err(error) => Err(error.into()),
+            },
         }
     }
 }
+
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
+pub enum AscDesc {
+    Asc(String),
+    Desc(String),
+}
+
+impl AscDesc {
+    pub fn field(&self) -> &str {
+        match self {
+            AscDesc::Asc(field) => field,
+            AscDesc::Desc(field) => field,
+        }
+    }
+}
+
+impl FromStr for AscDesc {
+    type Err = UserError;
+
+    fn from_str(text: &str) -> Result<AscDesc, Self::Err> {
+        match text.rsplit_once(':') {
+            Some((field_name, "asc")) => Ok(AscDesc::Asc(field_name.to_string())),
+            Some((field_name, "desc")) => Ok(AscDesc::Desc(field_name.to_string())),
+            _ => Err(UserError::InvalidCriterionName { name: text.to_string() }),
         }
     }
 }
@@ -74,6 +89,7 @@ pub fn default_criteria() -> Vec<Criterion> {
     vec![
         Criterion::Words,
         Criterion::Typo,
+        Criterion::Sort,
         Criterion::Proximity,
         Criterion::Attribute,
         Criterion::Exactness,
@@ -87,11 +103,12 @@ impl fmt::Display for Criterion {
         match self {
             Words => f.write_str("words"),
             Typo => f.write_str("typo"),
+            Sort => f.write_str("sort"),
             Proximity => f.write_str("proximity"),
             Attribute => f.write_str("attribute"),
             Exactness => f.write_str("exactness"),
-            Asc(attr) => write!(f, "asc({})", attr),
-            Desc(attr) => write!(f, "desc({})", attr),
+            Asc(attr) => write!(f, "{}:asc", attr),
+            Desc(attr) => write!(f, "{}:desc", attr),
         }
     }
 }

milli/src/error.rs

@@ -58,6 +58,7 @@ pub enum UserError {
     InvalidFacetsDistribution { invalid_facets_name: HashSet<String> },
     InvalidFilter(pest::error::Error<ParserRule>),
     InvalidFilterAttribute(pest::error::Error<ParserRule>),
+    InvalidSortableAttribute { field: String, valid_fields: HashSet<String> },
     InvalidStoreFile,
     MaxDatabaseSizeReached,
     MissingDocumentId { document: Object },
@@ -226,6 +227,15 @@ only composed of alphanumeric characters (a-z A-Z 0-9), hyphens (-) and undersco
                 )
             }
             Self::InvalidFilterAttribute(error) => error.fmt(f),
+            Self::InvalidSortableAttribute { field, valid_fields } => {
+                let valid_names =
+                    valid_fields.iter().map(AsRef::as_ref).collect::<Vec<_>>().join(", ");
+                write!(
+                    f,
+                    "Attribute {} is not sortable, available sortable attributes are: {}",
+                    field, valid_names
+                )
+            }
             Self::MissingDocumentId { document } => {
                 let json = serde_json::to_string(document).unwrap();
                 write!(f, "document doesn't have an identifier {}", json)

milli/src/index.rs

@@ -28,6 +28,7 @@ pub mod main_key {
     pub const DISTINCT_FIELD_KEY: &str = "distinct-field-key";
     pub const DOCUMENTS_IDS_KEY: &str = "documents-ids";
     pub const FILTERABLE_FIELDS_KEY: &str = "filterable-fields";
+    pub const SORTABLE_FIELDS_KEY: &str = "sortable-fields";
     pub const FIELD_DISTRIBUTION_KEY: &str = "fields-distribution";
     pub const FIELDS_IDS_MAP_KEY: &str = "fields-ids-map";
     pub const HARD_EXTERNAL_DOCUMENTS_IDS_KEY: &str = "hard-external-documents-ids";
@@ -446,13 +447,45 @@ impl Index {
         Ok(fields_ids)
     }
 
+    /* sortable fields */
+
+    /// Writes the sortable fields names in the database.
+    pub(crate) fn put_sortable_fields(
+        &self,
+        wtxn: &mut RwTxn,
+        fields: &HashSet<String>,
+    ) -> heed::Result<()> {
+        self.main.put::<_, Str, SerdeJson<_>>(wtxn, main_key::SORTABLE_FIELDS_KEY, fields)
+    }
+
+    /// Deletes the sortable fields ids in the database.
+    pub(crate) fn delete_sortable_fields(&self, wtxn: &mut RwTxn) -> heed::Result<bool> {
+        self.main.delete::<_, Str>(wtxn, main_key::SORTABLE_FIELDS_KEY)
+    }
+
+    /// Returns the sortable fields names.
+    pub fn sortable_fields(&self, rtxn: &RoTxn) -> heed::Result<HashSet<String>> {
+        Ok(self
+            .main
+            .get::<_, Str, SerdeJson<_>>(rtxn, main_key::SORTABLE_FIELDS_KEY)?
+            .unwrap_or_default())
+    }
+
+    /// Identical to `sortable_fields`, but returns ids instead.
+    pub fn sortable_fields_ids(&self, rtxn: &RoTxn) -> Result<HashSet<FieldId>> {
+        let fields = self.sortable_fields(rtxn)?;
+        let fields_ids_map = self.fields_ids_map(rtxn)?;
+        Ok(fields.into_iter().filter_map(|name| fields_ids_map.id(&name)).collect())
+    }
+
     /* faceted documents ids */
 
     /// Returns the faceted fields names.
     ///
-    /// Faceted fields are the union of all the filterable, distinct, and Asc/Desc fields.
+    /// Faceted fields are the union of all the filterable, sortable, distinct, and Asc/Desc fields.
     pub fn faceted_fields(&self, rtxn: &RoTxn) -> Result<HashSet<String>> {
         let filterable_fields = self.filterable_fields(rtxn)?;
+        let sortable_fields = self.sortable_fields(rtxn)?;
         let distinct_field = self.distinct_field(rtxn)?;
         let asc_desc_fields =
             self.criteria(rtxn)?.into_iter().filter_map(|criterion| match criterion {
@@ -461,6 +494,7 @@ impl Index {
             });
 
         let mut faceted_fields = filterable_fields;
+        faceted_fields.extend(sortable_fields);
         faceted_fields.extend(asc_desc_fields);
         if let Some(field) = distinct_field {
             faceted_fields.insert(field.to_owned());

milli/src/lib.rs

@@ -22,7 +22,7 @@ use std::result::Result as StdResult;
 use fxhash::{FxHasher32, FxHasher64};
 use serde_json::{Map, Value};
 
-pub use self::criterion::{default_criteria, Criterion};
+pub use self::criterion::{default_criteria, AscDesc, Criterion};
 pub use self::error::{
     Error, FieldIdMapMissingEntry, InternalError, SerializationError, UserError,
 };

milli/src/search/criteria/asc_desc.rs

@@ -7,7 +7,7 @@ use roaring::RoaringBitmap;
 
 use super::{Criterion, CriterionParameters, CriterionResult};
 use crate::search::criteria::{resolve_query_tree, CriteriaBuilder};
-use crate::search::facet::FacetNumberIter;
+use crate::search::facet::{FacetNumberIter, FacetStringIter};
 use crate::search::query_tree::Operation;
 use crate::{FieldId, Index, Result};
 
@@ -20,7 +20,7 @@ pub struct AscDesc<'t> {
     rtxn: &'t heed::RoTxn<'t>,
     field_name: String,
     field_id: Option<FieldId>,
-    ascending: bool,
+    is_ascending: bool,
     query_tree: Option<Operation>,
     candidates: Box<dyn Iterator<Item = heed::Result<RoaringBitmap>> + 't>,
     allowed_candidates: RoaringBitmap,
@@ -53,12 +53,16 @@ impl<'t> AscDesc<'t> {
         rtxn: &'t heed::RoTxn,
         parent: Box<dyn Criterion + 't>,
         field_name: String,
-        ascending: bool,
+        is_ascending: bool,
     ) -> Result<Self> {
         let fields_ids_map = index.fields_ids_map(rtxn)?;
         let field_id = fields_ids_map.id(&field_name);
         let faceted_candidates = match field_id {
-            Some(field_id) => index.number_faceted_documents_ids(rtxn, field_id)?,
+            Some(field_id) => {
+                let number_faceted = index.number_faceted_documents_ids(rtxn, field_id)?;
+                let string_faceted = index.string_faceted_documents_ids(rtxn, field_id)?;
+                number_faceted | string_faceted
+            }
             None => RoaringBitmap::default(),
         };
 
@@ -67,7 +71,7 @@ impl<'t> AscDesc<'t> {
             rtxn,
             field_name,
             field_id,
-            ascending,
+            is_ascending,
             query_tree: None,
             candidates: Box::new(std::iter::empty()),
             allowed_candidates: RoaringBitmap::new(),
@@ -87,7 +91,7 @@ impl<'t> Criterion for AscDesc<'t> {
         loop {
             debug!(
                 "Facet {}({}) iteration",
-                if self.ascending { "Asc" } else { "Desc" },
+                if self.is_ascending { "Asc" } else { "Desc" },
                 self.field_name
             );
 
@@ -136,7 +140,7 @@ impl<'t> Criterion for AscDesc<'t> {
                                 self.index,
                                 self.rtxn,
                                 field_id,
-                                self.ascending,
+                                self.is_ascending,
                                 candidates & &self.faceted_candidates,
                             )?,
                             None => Box::new(std::iter::empty()),
@@ -167,31 +171,49 @@ fn facet_ordered<'t>(
     index: &'t Index,
     rtxn: &'t heed::RoTxn,
     field_id: FieldId,
-    ascending: bool,
+    is_ascending: bool,
     candidates: RoaringBitmap,
 ) -> Result<Box<dyn Iterator<Item = heed::Result<RoaringBitmap>> + 't>> {
     if candidates.len() <= CANDIDATES_THRESHOLD {
-        let iter = iterative_facet_ordered_iter(index, rtxn, field_id, ascending, candidates)?;
-        Ok(Box::new(iter.map(Ok)) as Box<dyn Iterator<Item = _>>)
+        let number_iter = iterative_facet_number_ordered_iter(
+            index,
+            rtxn,
+            field_id,
+            is_ascending,
+            candidates.clone(),
+        )?;
+        let string_iter =
+            iterative_facet_string_ordered_iter(index, rtxn, field_id, is_ascending, candidates)?;
+        Ok(Box::new(number_iter.chain(string_iter).map(Ok)) as Box<dyn Iterator<Item = _>>)
     } else {
-        let facet_fn = if ascending {
+        let facet_number_fn = if is_ascending {
             FacetNumberIter::new_reducing
         } else {
             FacetNumberIter::new_reverse_reducing
         };
-        let iter = facet_fn(rtxn, index, field_id, candidates)?;
-        Ok(Box::new(iter.map(|res| res.map(|(_, docids)| docids))))
+        let number_iter = facet_number_fn(rtxn, index, field_id, candidates.clone())?
+            .map(|res| res.map(|(_, docids)| docids));
+
+        let facet_string_fn = if is_ascending {
+            FacetStringIter::new_reducing
+        } else {
+            FacetStringIter::new_reverse_reducing
+        };
+        let string_iter = facet_string_fn(rtxn, index, field_id, candidates)?
+            .map(|res| res.map(|(_, _, docids)| docids));
+
+        Ok(Box::new(number_iter.chain(string_iter)))
     }
 }
 
-/// Fetch the whole list of candidates facet values one by one and order them by it.
+/// Fetch the whole list of candidates facet number values one by one and order them by it.
 ///
 /// This function is fast when the amount of candidates to rank is small.
-fn iterative_facet_ordered_iter<'t>(
+fn iterative_facet_number_ordered_iter<'t>(
     index: &'t Index,
     rtxn: &'t heed::RoTxn,
     field_id: FieldId,
-    ascending: bool,
+    is_ascending: bool,
     candidates: RoaringBitmap,
 ) -> Result<impl Iterator<Item = RoaringBitmap> + 't> {
     let mut docids_values = Vec::with_capacity(candidates.len() as usize);
@@ -199,14 +221,14 @@ fn iterative_facet_ordered_iter<'t>(
         let left = (field_id, docid, f64::MIN);
         let right = (field_id, docid, f64::MAX);
         let mut iter = index.field_id_docid_facet_f64s.range(rtxn, &(left..=right))?;
-        let entry = if ascending { iter.next() } else { iter.last() };
+        let entry = if is_ascending { iter.next() } else { iter.last() };
         if let Some(((_, _, value), ())) = entry.transpose()? {
             docids_values.push((docid, OrderedFloat(value)));
         }
     }
     docids_values.sort_unstable_by_key(|(_, v)| *v);
     let iter = docids_values.into_iter();
-    let iter = if ascending {
+    let iter = if is_ascending {
         Box::new(iter) as Box<dyn Iterator<Item = _>>
     } else {
         Box::new(iter.rev())
@@ -216,7 +238,49 @@ fn iterative_facet_ordered_iter<'t>(
     // required to collect the result into an owned collection (a Vec).
     // https://github.com/rust-itertools/itertools/issues/499
     let vec: Vec<_> = iter
-        .group_by(|(_, v)| v.clone())
+        .group_by(|(_, v)| *v)
+        .into_iter()
+        .map(|(_, ids)| ids.map(|(id, _)| id).collect())
+        .collect();
+
+    Ok(vec.into_iter())
+}
+
+/// Fetch the whole list of candidates facet string values one by one and order them by it.
+///
+/// This function is fast when the amount of candidates to rank is small.
+fn iterative_facet_string_ordered_iter<'t>(
+    index: &'t Index,
+    rtxn: &'t heed::RoTxn,
+    field_id: FieldId,
+    is_ascending: bool,
+    candidates: RoaringBitmap,
+) -> Result<impl Iterator<Item = RoaringBitmap> + 't> {
+    let mut docids_values = Vec::with_capacity(candidates.len() as usize);
+    for docid in candidates.iter() {
+        let left = (field_id, docid, "");
+        let right = (field_id, docid.saturating_add(1), "");
+        // FIXME Doing this means that it will never be possible to retrieve
+        //       the document with id 2^32, not sure this is a real problem.
+        let mut iter = index.field_id_docid_facet_strings.range(rtxn, &(left..right))?;
+        let entry = if is_ascending { iter.next() } else { iter.last() };
+        if let Some(((_, _, value), _)) = entry.transpose()? {
+            docids_values.push((docid, value));
+        }
+    }
+    docids_values.sort_unstable_by_key(|(_, v)| *v);
+    let iter = docids_values.into_iter();
+    let iter = if is_ascending {
+        Box::new(iter) as Box<dyn Iterator<Item = _>>
+    } else {
+        Box::new(iter.rev())
+    };
+
+    // The itertools GroupBy iterator doesn't provide an owned version, we are therefore
+    // required to collect the result into an owned collection (a Vec).
+    // https://github.com/rust-itertools/itertools/issues/499
+    let vec: Vec<_> = iter
+        .group_by(|(_, v)| *v)
         .into_iter()
         .map(|(_, ids)| ids.map(|(id, _)| id).collect())
         .collect();

milli/src/search/criteria/mod.rs

@@ -12,6 +12,7 @@ use self::r#final::Final;
 use self::typo::Typo;
 use self::words::Words;
 use super::query_tree::{Operation, PrimitiveQueryPart, Query, QueryKind};
+use crate::criterion::AscDesc as AscDescName;
 use crate::search::{word_derivations, WordDerivationsCache};
 use crate::{DocumentId, FieldId, Index, Result, TreeLevel};
 
@@ -273,6 +274,7 @@ impl<'t> CriteriaBuilder<'t> {
         query_tree: Option<Operation>,
         primitive_query: Option<Vec<PrimitiveQueryPart>>,
         filtered_candidates: Option<RoaringBitmap>,
+        sort_criteria: Option<Vec<AscDescName>>,
     ) -> Result<Final<'t>> {
         use crate::criterion::Criterion as Name;
 
@@ -282,8 +284,30 @@ impl<'t> CriteriaBuilder<'t> {
             Box::new(Initial::new(query_tree, filtered_candidates)) as Box<dyn Criterion>;
         for name in self.index.criteria(&self.rtxn)? {
             criterion = match name {
-                Name::Typo => Box::new(Typo::new(self, criterion)),
                 Name::Words => Box::new(Words::new(self, criterion)),
+                Name::Typo => Box::new(Typo::new(self, criterion)),
+                Name::Sort => match sort_criteria {
+                    Some(ref sort_criteria) => {
+                        for asc_desc in sort_criteria {
+                            criterion = match asc_desc {
+                                AscDescName::Asc(field) => Box::new(AscDesc::asc(
+                                    &self.index,
+                                    &self.rtxn,
+                                    criterion,
+                                    field.to_string(),
+                                )?),
+                                AscDescName::Desc(field) => Box::new(AscDesc::desc(
+                                    &self.index,
+                                    &self.rtxn,
+                                    criterion,
+                                    field.to_string(),
+                                )?),
+                            };
+                        }
+                        criterion
+                    }
+                    None => criterion,
+                },
                 Name::Proximity => Box::new(Proximity::new(self, criterion)),
                 Name::Attribute => Box::new(Attribute::new(self, criterion)),
                 Name::Exactness => Box::new(Exactness::new(self, criterion, &primitive_query)?),

milli/src/search/facet/facet_string.rs

@@ -131,7 +131,7 @@ use std::ops::Bound::{Excluded, Included, Unbounded};
 
 use either::{Either, Left, Right};
 use heed::types::{ByteSlice, DecodeIgnore};
-use heed::{Database, LazyDecode, RoRange};
+use heed::{Database, LazyDecode, RoRange, RoRevRange};
 use roaring::RoaringBitmap;
 
 use crate::heed_codec::facet::{
@@ -206,6 +206,65 @@ impl<'t> Iterator for FacetStringGroupRange<'t> {
     }
 }
 
+pub struct FacetStringGroupRevRange<'t> {
+    iter: RoRevRange<
+        't,
+        FacetLevelValueU32Codec,
+        LazyDecode<FacetStringZeroBoundsValueCodec<CboRoaringBitmapCodec>>,
+    >,
+    end: Bound<u32>,
+}
+
+impl<'t> FacetStringGroupRevRange<'t> {
+    pub fn new<X, Y>(
+        rtxn: &'t heed::RoTxn,
+        db: Database<X, Y>,
+        field_id: FieldId,
+        level: NonZeroU8,
+        left: Bound<u32>,
+        right: Bound<u32>,
+    ) -> heed::Result<FacetStringGroupRevRange<'t>> {
+        let db = db.remap_types::<
+            FacetLevelValueU32Codec,
+            FacetStringZeroBoundsValueCodec<CboRoaringBitmapCodec>,
+        >();
+        let left_bound = match left {
+            Included(left) => Included((field_id, level, left, u32::MIN)),
+            Excluded(left) => Excluded((field_id, level, left, u32::MIN)),
+            Unbounded => Included((field_id, level, u32::MIN, u32::MIN)),
+        };
+        let right_bound = Included((field_id, level, u32::MAX, u32::MAX));
+        let iter = db.lazily_decode_data().rev_range(rtxn, &(left_bound, right_bound))?;
+        Ok(FacetStringGroupRevRange { iter, end: right })
+    }
+}
+
+impl<'t> Iterator for FacetStringGroupRevRange<'t> {
+    type Item = heed::Result<((NonZeroU8, u32, u32), (Option<(&'t str, &'t str)>, RoaringBitmap))>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.iter.next() {
+            Some(Ok(((_fid, level, left, right), docids))) => {
+                let must_be_returned = match self.end {
+                    Included(end) => right <= end,
+                    Excluded(end) => right < end,
+                    Unbounded => true,
+                };
+                if must_be_returned {
+                    match docids.decode() {
+                        Ok((bounds, docids)) => Some(Ok(((level, left, right), (bounds, docids)))),
+                        Err(e) => Some(Err(e)),
+                    }
+                } else {
+                    None
+                }
+            }
+            Some(Err(e)) => Some(Err(e)),
+            None => None,
+        }
+    }
+}
+
 /// An iterator that is used to explore the level 0 of the facets string database.
 ///
 /// It yields the facet string and the roaring bitmap associated with it.
@@ -280,6 +339,81 @@ impl<'t> Iterator for FacetStringLevelZeroRange<'t> {
     }
 }
 
+pub struct FacetStringLevelZeroRevRange<'t> {
+    iter: RoRevRange<
+        't,
+        FacetStringLevelZeroCodec,
+        FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>,
+    >,
+}
+
+impl<'t> FacetStringLevelZeroRevRange<'t> {
+    pub fn new<X, Y>(
+        rtxn: &'t heed::RoTxn,
+        db: Database<X, Y>,
+        field_id: FieldId,
+        left: Bound<&str>,
+        right: Bound<&str>,
+    ) -> heed::Result<FacetStringLevelZeroRevRange<'t>> {
+        fn encode_value<'a>(buffer: &'a mut Vec<u8>, field_id: FieldId, value: &str) -> &'a [u8] {
+            buffer.extend_from_slice(&field_id.to_be_bytes());
+            buffer.push(0);
+            buffer.extend_from_slice(value.as_bytes());
+            &buffer[..]
+        }
+
+        let mut left_buffer = Vec::new();
+        let left_bound = match left {
+            Included(value) => Included(encode_value(&mut left_buffer, field_id, value)),
+            Excluded(value) => Excluded(encode_value(&mut left_buffer, field_id, value)),
+            Unbounded => {
+                left_buffer.extend_from_slice(&field_id.to_be_bytes());
+                left_buffer.push(0);
+                Included(&left_buffer[..])
+            }
+        };
+
+        let mut right_buffer = Vec::new();
+        let right_bound = match right {
+            Included(value) => Included(encode_value(&mut right_buffer, field_id, value)),
+            Excluded(value) => Excluded(encode_value(&mut right_buffer, field_id, value)),
+            Unbounded => {
+                right_buffer.extend_from_slice(&field_id.to_be_bytes());
+                right_buffer.push(1); // we must only get the level 0
+                Excluded(&right_buffer[..])
+            }
+        };
+
+        let iter = db
+            .remap_key_type::<ByteSlice>()
+            .rev_range(rtxn, &(left_bound, right_bound))?
+            .remap_types::<
+                FacetStringLevelZeroCodec,
+                FacetStringLevelZeroValueCodec<CboRoaringBitmapCodec>
+            >();
+
+        Ok(FacetStringLevelZeroRevRange { iter })
+    }
+}
+
+impl<'t> Iterator for FacetStringLevelZeroRevRange<'t> {
+    type Item = heed::Result<(&'t str, &'t str, RoaringBitmap)>;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        match self.iter.next() {
+            Some(Ok(((_fid, normalized), (original, docids)))) => {
+                Some(Ok((normalized, original, docids)))
+            }
+            Some(Err(e)) => Some(Err(e)),
+            None => None,
+        }
+    }
+}
+
+type EitherStringRange<'t> = Either<FacetStringGroupRange<'t>, FacetStringLevelZeroRange<'t>>;
+type EitherStringRevRange<'t> =
+    Either<FacetStringGroupRevRange<'t>, FacetStringLevelZeroRevRange<'t>>;
+
 /// An iterator that is used to explore the facet strings level by level,
 /// it will only return facets strings that are associated with the
 /// candidates documents ids given.
@@ -287,12 +421,45 @@ pub struct FacetStringIter<'t> {
     rtxn: &'t heed::RoTxn<'t>,
     db: Database<ByteSlice, ByteSlice>,
     field_id: FieldId,
-    level_iters:
-        Vec<(RoaringBitmap, Either<FacetStringGroupRange<'t>, FacetStringLevelZeroRange<'t>>)>,
+    level_iters: Vec<(RoaringBitmap, Either<EitherStringRange<'t>, EitherStringRevRange<'t>>)>,
     must_reduce: bool,
 }
 
 impl<'t> FacetStringIter<'t> {
+    pub fn new_reducing(
+        rtxn: &'t heed::RoTxn,
+        index: &'t Index,
+        field_id: FieldId,
+        documents_ids: RoaringBitmap,
+    ) -> heed::Result<FacetStringIter<'t>> {
+        let db = index.facet_id_string_docids.remap_types::<ByteSlice, ByteSlice>();
+        let highest_iter = Self::highest_iter(rtxn, index, db, field_id)?;
+        Ok(FacetStringIter {
+            rtxn,
+            db,
+            field_id,
+            level_iters: vec![(documents_ids, Left(highest_iter))],
+            must_reduce: true,
+        })
+    }
+
+    pub fn new_reverse_reducing(
+        rtxn: &'t heed::RoTxn,
+        index: &'t Index,
+        field_id: FieldId,
+        documents_ids: RoaringBitmap,
+    ) -> heed::Result<FacetStringIter<'t>> {
+        let db = index.facet_id_string_docids.remap_types::<ByteSlice, ByteSlice>();
+        let highest_reverse_iter = Self::highest_reverse_iter(rtxn, index, db, field_id)?;
+        Ok(FacetStringIter {
+            rtxn,
+            db,
+            field_id,
+            level_iters: vec![(documents_ids, Right(highest_reverse_iter))],
+            must_reduce: true,
+        })
+    }
+
     pub fn new_non_reducing(
         rtxn: &'t heed::RoTxn,
         index: &'t Index,
@@ -300,30 +467,12 @@ impl<'t> FacetStringIter<'t> {
         documents_ids: RoaringBitmap,
     ) -> heed::Result<FacetStringIter<'t>> {
         let db = index.facet_id_string_docids.remap_types::<ByteSlice, ByteSlice>();
-        let highest_level = Self::highest_level(rtxn, db, field_id)?.unwrap_or(0);
-        let highest_iter = match NonZeroU8::new(highest_level) {
-            Some(highest_level) => Left(FacetStringGroupRange::new(
-                rtxn,
-                index.facet_id_string_docids,
-                field_id,
-                highest_level,
-                Unbounded,
-                Unbounded,
-            )?),
-            None => Right(FacetStringLevelZeroRange::new(
-                rtxn,
-                index.facet_id_string_docids,
-                field_id,
-                Unbounded,
-                Unbounded,
-            )?),
-        };
-
+        let highest_iter = Self::highest_iter(rtxn, index, db, field_id)?;
         Ok(FacetStringIter {
             rtxn,
             db,
             field_id,
-            level_iters: vec![(documents_ids, highest_iter)],
+            level_iters: vec![(documents_ids, Left(highest_iter))],
             must_reduce: false,
         })
     }
@@ -340,6 +489,62 @@ impl<'t> FacetStringIter<'t> {
             .transpose()?
             .map(|(key_bytes, _)| key_bytes[2])) // the level is the third bit
     }
+
+    fn highest_iter<X, Y>(
+        rtxn: &'t heed::RoTxn,
+        index: &'t Index,
+        db: Database<X, Y>,
+        field_id: FieldId,
+    ) -> heed::Result<Either<FacetStringGroupRange<'t>, FacetStringLevelZeroRange<'t>>> {
+        let highest_level = Self::highest_level(rtxn, db, field_id)?.unwrap_or(0);
+        match NonZeroU8::new(highest_level) {
+            Some(highest_level) => FacetStringGroupRange::new(
+                rtxn,
+                index.facet_id_string_docids,
+                field_id,
+                highest_level,
+                Unbounded,
+                Unbounded,
+            )
+            .map(Left),
+            None => FacetStringLevelZeroRange::new(
+                rtxn,
+                index.facet_id_string_docids,
+                field_id,
+                Unbounded,
+                Unbounded,
+            )
+            .map(Right),
+        }
+    }
+
+    fn highest_reverse_iter<X, Y>(
+        rtxn: &'t heed::RoTxn,
+        index: &'t Index,
+        db: Database<X, Y>,
+        field_id: FieldId,
+    ) -> heed::Result<Either<FacetStringGroupRevRange<'t>, FacetStringLevelZeroRevRange<'t>>> {
+        let highest_level = Self::highest_level(rtxn, db, field_id)?.unwrap_or(0);
+        match NonZeroU8::new(highest_level) {
+            Some(highest_level) => FacetStringGroupRevRange::new(
+                rtxn,
+                index.facet_id_string_docids,
+                field_id,
+                highest_level,
+                Unbounded,
+                Unbounded,
+            )
+            .map(Left),
+            None => FacetStringLevelZeroRevRange::new(
+                rtxn,
+                index.facet_id_string_docids,
+                field_id,
+                Unbounded,
+                Unbounded,
+            )
+            .map(Right),
+        }
+    }
 }
 
 impl<'t> Iterator for FacetStringIter<'t> {
@@ -348,6 +553,21 @@ impl<'t> Iterator for FacetStringIter<'t> {
     fn next(&mut self) -> Option<Self::Item> {
         'outer: loop {
             let (documents_ids, last) = self.level_iters.last_mut()?;
+            let is_ascending = last.is_left();
+
+            // We remap the different iterator types to make
+            // the algorithm less complex to understand.
+            let last = match last {
+                Left(ascending) => match ascending {
+                    Left(last) => Left(Left(last)),
+                    Right(last) => Right(Left(last)),
+                },
+                Right(descending) => match descending {
+                    Left(last) => Left(Right(last)),
+                    Right(last) => Right(Right(last)),
+                },
+            };
+
             match last {
                 Left(last) => {
                     for result in last {
@@ -359,7 +579,31 @@ impl<'t> Iterator for FacetStringIter<'t> {
                                         *documents_ids -= &docids;
                                     }
 
-                                    let result = match string_bounds {
+                                    let result = if is_ascending {
+                                        match string_bounds {
+                                            Some((left, right)) => {
+                                                FacetStringLevelZeroRevRange::new(
+                                                    self.rtxn,
+                                                    self.db,
+                                                    self.field_id,
+                                                    Included(left),
+                                                    Included(right),
+                                                )
+                                                .map(Right)
+                                            }
+                                            None => FacetStringGroupRevRange::new(
+                                                self.rtxn,
+                                                self.db,
+                                                self.field_id,
+                                                NonZeroU8::new(level.get() - 1).unwrap(),
+                                                Included(left),
+                                                Included(right),
+                                            )
+                                            .map(Left),
+                                        }
+                                        .map(Right)
+                                    } else {
+                                        match string_bounds {
                                             Some((left, right)) => FacetStringLevelZeroRange::new(
                                                 self.rtxn,
                                                 self.db,
@@ -377,6 +621,8 @@ impl<'t> Iterator for FacetStringIter<'t> {
                                                 Included(right),
                                             )
                                             .map(Left),
+                                        }
+                                        .map(Left)
                                     };
 
                                     match result {

milli/src/search/mod.rs

@@ -18,6 +18,8 @@ pub(crate) use self::facet::ParserRule;
 pub use self::facet::{FacetDistribution, FacetNumberIter, FilterCondition, Operator};
 pub use self::matching_words::MatchingWords;
 use self::query_tree::QueryTreeBuilder;
+use crate::criterion::AscDesc;
+use crate::error::UserError;
 use crate::search::criteria::r#final::{Final, FinalResult};
 use crate::{DocumentId, Index, Result};
 
@@ -37,6 +39,7 @@ pub struct Search<'a> {
     filter: Option<FilterCondition>,
     offset: usize,
     limit: usize,
+    sort_criteria: Option<Vec<AscDesc>>,
     optional_words: bool,
     authorize_typos: bool,
     words_limit: usize,
@@ -51,6 +54,7 @@ impl<'a> Search<'a> {
             filter: None,
             offset: 0,
             limit: 20,
+            sort_criteria: None,
             optional_words: true,
             authorize_typos: true,
             words_limit: 10,
@@ -74,6 +78,11 @@ impl<'a> Search<'a> {
         self
     }
 
+    pub fn sort_criteria(&mut self, criteria: Vec<AscDesc>) -> &mut Search<'a> {
+        self.sort_criteria = Some(criteria);
+        self
+    }
+
     pub fn optional_words(&mut self, value: bool) -> &mut Search<'a> {
         self.optional_words = value;
         self
@@ -134,8 +143,29 @@ impl<'a> Search<'a> {
             None => MatchingWords::default(),
         };
 
+        // We check that we are allowed to use the sort criteria, we check
+        // that they are declared in the sortable fields.
+        let sortable_fields = self.index.sortable_fields(self.rtxn)?;
+        if let Some(sort_criteria) = &self.sort_criteria {
+            for asc_desc in sort_criteria {
+                let field = asc_desc.field();
+                if !sortable_fields.contains(field) {
+                    return Err(UserError::InvalidSortableAttribute {
+                        field: field.to_string(),
+                        valid_fields: sortable_fields,
+                    }
+                    .into());
+                }
+            }
+        }
+
         let criteria_builder = criteria::CriteriaBuilder::new(self.rtxn, self.index)?;
-        let criteria = criteria_builder.build(query_tree, primitive_query, filtered_candidates)?;
+        let criteria = criteria_builder.build(
+            query_tree,
+            primitive_query,
+            filtered_candidates,
+            self.sort_criteria.clone(),
+        )?;
 
         match self.index.distinct_field(self.rtxn)? {
             None => self.perform_sort(NoopDistinct, matching_words, criteria),
@@ -199,6 +229,7 @@ impl fmt::Debug for Search<'_> {
             filter,
             offset,
             limit,
+            sort_criteria,
             optional_words,
             authorize_typos,
             words_limit,
@@ -210,6 +241,7 @@ impl fmt::Debug for Search<'_> {
             .field("filter", filter)
             .field("offset", offset)
             .field("limit", limit)
+            .field("sort_criteria", sort_criteria)
             .field("optional_words", optional_words)
             .field("authorize_typos", authorize_typos)
             .field("words_limit", words_limit)

milli/src/update/settings.rs

@@ -75,6 +75,7 @@ pub struct Settings<'a, 't, 'u, 'i> {
     searchable_fields: Setting<Vec<String>>,
     displayed_fields: Setting<Vec<String>>,
     filterable_fields: Setting<HashSet<String>>,
+    sortable_fields: Setting<HashSet<String>>,
     criteria: Setting<Vec<String>>,
     stop_words: Setting<BTreeSet<String>>,
     distinct_field: Setting<String>,
@@ -102,6 +103,7 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
             searchable_fields: Setting::NotSet,
             displayed_fields: Setting::NotSet,
             filterable_fields: Setting::NotSet,
+            sortable_fields: Setting::NotSet,
             criteria: Setting::NotSet,
             stop_words: Setting::NotSet,
             distinct_field: Setting::NotSet,
@@ -135,6 +137,10 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
         self.filterable_fields = Setting::Set(names);
     }
 
+    pub fn set_sortable_fields(&mut self, names: HashSet<String>) {
+        self.sortable_fields = Setting::Set(names);
+    }
+
     pub fn reset_criteria(&mut self) {
         self.criteria = Setting::Reset;
     }
@@ -392,6 +398,23 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
         Ok(())
     }
 
+    fn update_sortable(&mut self) -> Result<()> {
+        match self.sortable_fields {
+            Setting::Set(ref fields) => {
+                let mut new_fields = HashSet::new();
+                for name in fields {
+                    new_fields.insert(name.clone());
+                }
+                self.index.put_sortable_fields(self.wtxn, &new_fields)?;
+            }
+            Setting::Reset => {
+                self.index.delete_sortable_fields(self.wtxn)?;
+            }
+            Setting::NotSet => (),
+        }
+        Ok(())
+    }
+
     fn update_criteria(&mut self) -> Result<()> {
         match self.criteria {
             Setting::Set(ref fields) => {
@@ -446,6 +469,7 @@ impl<'a, 't, 'u, 'i> Settings<'a, 't, 'u, 'i> {
 
         self.update_displayed()?;
         self.update_filterable()?;
+        self.update_sortable()?;
         self.update_distinct_field()?;
         self.update_criteria()?;
         self.update_primary_key()?;
@@ -719,7 +743,7 @@ mod tests {
         let mut builder = Settings::new(&mut wtxn, &index, 0);
         // Don't display the generated `id` field.
         builder.set_displayed_fields(vec![S("name")]);
-        builder.set_criteria(vec![S("asc(age)")]);
+        builder.set_criteria(vec![S("age:asc")]);
         builder.execute(|_, _| ()).unwrap();
 
         // Then index some documents.
@@ -953,7 +977,7 @@ mod tests {
         let mut builder = Settings::new(&mut wtxn, &index, 0);
         builder.set_displayed_fields(vec!["hello".to_string()]);
         builder.set_filterable_fields(hashset! { S("age"), S("toto") });
-        builder.set_criteria(vec!["asc(toto)".to_string()]);
+        builder.set_criteria(vec!["toto:asc".to_string()]);
         builder.execute(|_, _| ()).unwrap();
         wtxn.commit().unwrap();
 
@@ -990,7 +1014,7 @@ mod tests {
         let mut builder = Settings::new(&mut wtxn, &index, 0);
         builder.set_displayed_fields(vec!["hello".to_string()]);
         // It is only Asc(toto), there is a facet database but it is denied to filter with toto.
-        builder.set_criteria(vec!["asc(toto)".to_string()]);
+        builder.set_criteria(vec!["toto:asc".to_string()]);
         builder.execute(|_, _| ()).unwrap();
         wtxn.commit().unwrap();
 

milli/tests/assets/test_set.ndjson

@@ -1,17 +1,17 @@
-{"id":"A","word_rank":0,"typo_rank":1,"proximity_rank":15,"attribute_rank":505,"exact_rank":5,"asc_desc_rank":0,"title":"hell o","description":"hell o is the fourteenth episode of the american television series glee performing songs with this word","tag":"blue","":""}
-{"id":"B","word_rank":2,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":4,"asc_desc_rank":1,"title":"hello","description":"hello is a song recorded by english singer songwriter adele","tag":"red","":""}
-{"id":"C","word_rank":0,"typo_rank":1,"proximity_rank":8,"attribute_rank":336,"exact_rank":4,"asc_desc_rank":2,"title":"hell on earth","description":"hell on earth is the third studio album by american hip hop duo mobb deep","tag":"blue","":""}
-{"id":"D","word_rank":0,"typo_rank":1,"proximity_rank":10,"attribute_rank":757,"exact_rank":4,"asc_desc_rank":3,"title":"hell on wheels tv series","description":"the construction of the first transcontinental railroad across the united states in the world","tag":"red","":""}
-{"id":"E","word_rank":2,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":4,"asc_desc_rank":4,"title":"hello kitty","description":"also known by her full name kitty white is a fictional character produced by the japanese company sanrio","tag":"green","":""}
-{"id":"F","word_rank":2,"typo_rank":1,"proximity_rank":0,"attribute_rank":1017,"exact_rank":5,"asc_desc_rank":5,"title":"laptop orchestra","description":"a laptop orchestra lork or lo is a chamber music ensemble consisting primarily of laptops like helo huddersfield experimental laptop orchestra","tag":"blue","":""}
-{"id":"G","word_rank":1,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":5,"title":"hello world film","description":"hello world is a 2019 japanese animated sci fi romantic drama film directed by tomohiko ito and produced by graphinica","tag":"red","":""}
-{"id":"H","word_rank":1,"typo_rank":0,"proximity_rank":1,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":4,"title":"world hello day","description":"holiday observed on november 21 to express that conflicts should be resolved through communication rather than the use of force","tag":"green","":""}
-{"id":"I","word_rank":0,"typo_rank":0,"proximity_rank":8,"attribute_rank":338,"exact_rank":3,"asc_desc_rank":3,"title":"hello world song","description":"hello world is a song written by tom douglas tony lane and david lee and recorded by american country music group lady antebellum","tag":"blue","":""}
-{"id":"J","word_rank":1,"typo_rank":0,"proximity_rank":1,"attribute_rank":1,"exact_rank":3,"asc_desc_rank":2,"title":"hello cruel world","description":"hello cruel world is an album by new zealand band tall dwarfs","tag":"green","":""}
-{"id":"K","word_rank":0,"typo_rank":2,"proximity_rank":9,"attribute_rank":670,"exact_rank":5,"asc_desc_rank":1,"title":"ello creation system","description":"in few word ello was a construction toy created by the american company mattel to engage girls in construction play","tag":"red","":""}
-{"id":"L","word_rank":0,"typo_rank":0,"proximity_rank":2,"attribute_rank":250,"exact_rank":4,"asc_desc_rank":0,"title":"good morning world","description":"good morning world is an american sitcom broadcast on cbs tv during the 1967 1968 season","tag":"blue","":""}
-{"id":"M","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":0,"asc_desc_rank":0,"title":"hello world america","description":"a perfect match for a perfect engine using the query hello world america","tag":"red","":""}
-{"id":"N","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":1,"asc_desc_rank":4,"title":"hello world america unleashed","description":"a very good match for a very good engine using the query hello world america","tag":"green","":""}
-{"id":"O","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":10,"exact_rank":0,"asc_desc_rank":6,"title":"a perfect match for a perfect engine using the query hello world america","description":"hello world america","tag":"blue","":""}
-{"id":"P","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":12,"exact_rank":1,"asc_desc_rank":3,"title":"a very good match for a very good engine using the query hello world america","description":"hello world america unleashed","tag":"red","":""}
-{"id":"Q","word_rank":1,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":2,"title":"hello world","description":"a hello world program generally is a computer program that outputs or displays the message hello world","tag":"green","":""}
+{"id":"A","word_rank":0,"typo_rank":1,"proximity_rank":15,"attribute_rank":505,"exact_rank":5,"asc_desc_rank":0,"sort_by_rank":0,"title":"hell o","description":"hell o is the fourteenth episode of the american television series glee performing songs with this word","tag":"blue","":""}
+{"id":"B","word_rank":2,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":4,"asc_desc_rank":1,"sort_by_rank":2,"title":"hello","description":"hello is a song recorded by english singer songwriter adele","tag":"red","":""}
+{"id":"C","word_rank":0,"typo_rank":1,"proximity_rank":8,"attribute_rank":336,"exact_rank":4,"asc_desc_rank":2,"sort_by_rank":0,"title":"hell on earth","description":"hell on earth is the third studio album by american hip hop duo mobb deep","tag":"blue","":""}
+{"id":"D","word_rank":0,"typo_rank":1,"proximity_rank":10,"attribute_rank":757,"exact_rank":4,"asc_desc_rank":3,"sort_by_rank":2,"title":"hell on wheels tv series","description":"the construction of the first transcontinental railroad across the united states in the world","tag":"red","":""}
+{"id":"E","word_rank":2,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":4,"asc_desc_rank":4,"sort_by_rank":1,"title":"hello kitty","description":"also known by her full name kitty white is a fictional character produced by the japanese company sanrio","tag":"green","":""}
+{"id":"F","word_rank":2,"typo_rank":1,"proximity_rank":0,"attribute_rank":1017,"exact_rank":5,"asc_desc_rank":5,"sort_by_rank":0,"title":"laptop orchestra","description":"a laptop orchestra lork or lo is a chamber music ensemble consisting primarily of laptops like helo huddersfield experimental laptop orchestra","tag":"blue","":""}
+{"id":"G","word_rank":1,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":5,"sort_by_rank":2,"title":"hello world film","description":"hello world is a 2019 japanese animated sci fi romantic drama film directed by tomohiko ito and produced by graphinica","tag":"red","":""}
+{"id":"H","word_rank":1,"typo_rank":0,"proximity_rank":1,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":4,"sort_by_rank":1,"title":"world hello day","description":"holiday observed on november 21 to express that conflicts should be resolved through communication rather than the use of force","tag":"green","":""}
+{"id":"I","word_rank":0,"typo_rank":0,"proximity_rank":8,"attribute_rank":338,"exact_rank":3,"asc_desc_rank":3,"sort_by_rank":0,"title":"hello world song","description":"hello world is a song written by tom douglas tony lane and david lee and recorded by american country music group lady antebellum","tag":"blue","":""}
+{"id":"J","word_rank":1,"typo_rank":0,"proximity_rank":1,"attribute_rank":1,"exact_rank":3,"asc_desc_rank":2,"sort_by_rank":1,"title":"hello cruel world","description":"hello cruel world is an album by new zealand band tall dwarfs","tag":"green","":""}
+{"id":"K","word_rank":0,"typo_rank":2,"proximity_rank":9,"attribute_rank":670,"exact_rank":5,"asc_desc_rank":1,"sort_by_rank":2,"title":"ello creation system","description":"in few word ello was a construction toy created by the american company mattel to engage girls in construction play","tag":"red","":""}
+{"id":"L","word_rank":0,"typo_rank":0,"proximity_rank":2,"attribute_rank":250,"exact_rank":4,"asc_desc_rank":0,"sort_by_rank":0,"title":"good morning world","description":"good morning world is an american sitcom broadcast on cbs tv during the 1967 1968 season","tag":"blue","":""}
+{"id":"M","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":0,"asc_desc_rank":0,"sort_by_rank":2,"title":"hello world america","description":"a perfect match for a perfect engine using the query hello world america","tag":"red","":""}
+{"id":"N","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":1,"asc_desc_rank":4,"sort_by_rank":1,"title":"hello world america unleashed","description":"a very good match for a very good engine using the query hello world america","tag":"green","":""}
+{"id":"O","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":10,"exact_rank":0,"asc_desc_rank":6,"sort_by_rank":0,"title":"a perfect match for a perfect engine using the query hello world america","description":"hello world america","tag":"blue","":""}
+{"id":"P","word_rank":0,"typo_rank":0,"proximity_rank":0,"attribute_rank":12,"exact_rank":1,"asc_desc_rank":3,"sort_by_rank":2,"title":"a very good match for a very good engine using the query hello world america","description":"hello world america unleashed","tag":"red","":""}
+{"id":"Q","word_rank":1,"typo_rank":0,"proximity_rank":0,"attribute_rank":0,"exact_rank":3,"asc_desc_rank":2,"sort_by_rank":1,"title":"hello world","description":"a hello world program generally is a computer program that outputs or displays the message hello world","tag":"green","":""}

milli/tests/search/distinct.rs

@@ -32,7 +32,7 @@ macro_rules! test_distinct {
             let SearchResult { documents_ids, .. } = search.execute().unwrap();
 
             let mut distinct_values = HashSet::new();
-            let expected_external_ids: Vec<_> = search::expected_order(&criteria, true, true)
+            let expected_external_ids: Vec<_> = search::expected_order(&criteria, true, true, &[])
                 .into_iter()
                 .filter_map(|d| {
                     if distinct_values.contains(&d.$distinct) {

milli/tests/search/filters.rs

@@ -29,7 +29,7 @@ macro_rules! test_filter {
             let SearchResult { documents_ids, .. } = search.execute().unwrap();
 
             let filtered_ids = search::expected_filtered_ids($filter);
-            let expected_external_ids: Vec<_> = search::expected_order(&criteria, true, true)
+            let expected_external_ids: Vec<_> = search::expected_order(&criteria, true, true, &[])
                 .into_iter()
                 .filter_map(|d| if filtered_ids.contains(&d.id) { Some(d.id) } else { None })
                 .collect();

milli/tests/search/mod.rs

@@ -1,3 +1,4 @@
+use std::cmp::Reverse;
 use std::collections::HashSet;
 
 use big_s::S;
@@ -5,7 +6,7 @@ use either::{Either, Left, Right};
 use heed::EnvOpenOptions;
 use maplit::{hashmap, hashset};
 use milli::update::{IndexDocuments, Settings, UpdateFormat};
-use milli::{Criterion, DocumentId, Index};
+use milli::{AscDesc, Criterion, DocumentId, Index};
 use serde::Deserialize;
 use slice_group_by::GroupBy;
 
@@ -36,6 +37,10 @@ pub fn setup_search_index_with_criteria(criteria: &[Criterion]) -> Index {
         S("tag"),
         S("asc_desc_rank"),
     });
+    builder.set_sortable_fields(hashset! {
+        S("tag"),
+        S("asc_desc_rank"),
+    });
     builder.set_synonyms(hashmap! {
         S("hello") => vec![S("good morning")],
         S("world") => vec![S("earth")],
@@ -67,6 +72,7 @@ pub fn expected_order(
     criteria: &[Criterion],
     authorize_typo: bool,
     optional_words: bool,
+    sort_by: &[AscDesc],
 ) -> Vec<TestDocument> {
     let dataset =
         serde_json::Deserializer::from_str(CONTENT).into_iter().map(|r| r.unwrap()).collect();
@@ -90,6 +96,14 @@ pub fn expected_order(
                     new_groups
                         .extend(group.linear_group_by_key(|d| d.proximity_rank).map(Vec::from));
                 }
+                Criterion::Sort if sort_by == [AscDesc::Asc(S("tag"))] => {
+                    group.sort_by_key(|d| d.sort_by_rank);
+                    new_groups.extend(group.linear_group_by_key(|d| d.sort_by_rank).map(Vec::from));
+                }
+                Criterion::Sort if sort_by == [AscDesc::Desc(S("tag"))] => {
+                    group.sort_by_key(|d| Reverse(d.sort_by_rank));
+                    new_groups.extend(group.linear_group_by_key(|d| d.sort_by_rank).map(Vec::from));
+                }
                 Criterion::Typo => {
                     group.sort_by_key(|d| d.typo_rank);
                     new_groups.extend(group.linear_group_by_key(|d| d.typo_rank).map(Vec::from));
@@ -104,11 +118,13 @@ pub fn expected_order(
                         .extend(group.linear_group_by_key(|d| d.asc_desc_rank).map(Vec::from));
                 }
                 Criterion::Desc(field_name) if field_name == "asc_desc_rank" => {
-                    group.sort_by_key(|d| std::cmp::Reverse(d.asc_desc_rank));
+                    group.sort_by_key(|d| Reverse(d.asc_desc_rank));
                     new_groups
                         .extend(group.linear_group_by_key(|d| d.asc_desc_rank).map(Vec::from));
                 }
-                Criterion::Asc(_) | Criterion::Desc(_) => new_groups.push(group.clone()),
+                Criterion::Asc(_) | Criterion::Desc(_) | Criterion::Sort => {
+                    new_groups.push(group.clone())
+                }
             }
         }
         groups = std::mem::take(&mut new_groups);
@@ -185,6 +201,7 @@ pub struct TestDocument {
     pub attribute_rank: u32,
     pub exact_rank: u32,
     pub asc_desc_rank: u32,
+    pub sort_by_rank: u32,
     pub title: String,
     pub description: String,
     pub tag: String,

milli/tests/search/query_criteria.rs

@@ -1,6 +1,6 @@
 use big_s::S;
 use milli::update::Settings;
-use milli::{Criterion, Search, SearchResult};
+use milli::{AscDesc, Criterion, Search, SearchResult};
 use Criterion::*;
 
 use crate::search::{self, EXTERNAL_DOCUMENTS_IDS};
@@ -11,7 +11,7 @@ const ALLOW_OPTIONAL_WORDS: bool = true;
 const DISALLOW_OPTIONAL_WORDS: bool = false;
 
 macro_rules! test_criterion {
-    ($func:ident, $optional_word:ident, $authorize_typos:ident, $criteria:expr) => {
+    ($func:ident, $optional_word:ident, $authorize_typos:ident, $criteria:expr, $sort_criteria:expr) => {
         #[test]
         fn $func() {
             let criteria = $criteria;
@@ -23,11 +23,16 @@ macro_rules! test_criterion {
             search.limit(EXTERNAL_DOCUMENTS_IDS.len());
             search.authorize_typos($authorize_typos);
             search.optional_words($optional_word);
+            search.sort_criteria($sort_criteria);
 
             let SearchResult { documents_ids, .. } = search.execute().unwrap();
 
-            let expected_external_ids: Vec<_> =
-                search::expected_order(&criteria, $authorize_typos, $optional_word)
+            let expected_external_ids: Vec<_> = search::expected_order(
+                &criteria,
+                $authorize_typos,
+                $optional_word,
+                &$sort_criteria[..],
+            )
             .into_iter()
             .map(|d| d.id)
             .collect();
@@ -37,68 +42,149 @@ macro_rules! test_criterion {
     };
 }
 
-test_criterion!(none_allow_typo, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![]);
-test_criterion!(none_disallow_typo, DISALLOW_OPTIONAL_WORDS, DISALLOW_TYPOS, vec![]);
-test_criterion!(words_allow_typo, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Words]);
-test_criterion!(attribute_allow_typo, DISALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Attribute]);
-test_criterion!(attribute_disallow_typo, DISALLOW_OPTIONAL_WORDS, DISALLOW_TYPOS, vec![Attribute]);
-test_criterion!(exactness_allow_typo, DISALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Exactness]);
-test_criterion!(exactness_disallow_typo, DISALLOW_OPTIONAL_WORDS, DISALLOW_TYPOS, vec![Exactness]);
-test_criterion!(proximity_allow_typo, DISALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Proximity]);
-test_criterion!(proximity_disallow_typo, DISALLOW_OPTIONAL_WORDS, DISALLOW_TYPOS, vec![Proximity]);
+test_criterion!(none_allow_typo, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![], vec![]);
+test_criterion!(none_disallow_typo, DISALLOW_OPTIONAL_WORDS, DISALLOW_TYPOS, vec![], vec![]);
+test_criterion!(words_allow_typo, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Words], vec![]);
+test_criterion!(
+    attribute_allow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    ALLOW_TYPOS,
+    vec![Attribute],
+    vec![]
+);
+test_criterion!(
+    attribute_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Attribute],
+    vec![]
+);
+test_criterion!(
+    exactness_allow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    ALLOW_TYPOS,
+    vec![Exactness],
+    vec![]
+);
+test_criterion!(
+    exactness_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Exactness],
+    vec![]
+);
+test_criterion!(
+    proximity_allow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    ALLOW_TYPOS,
+    vec![Proximity],
+    vec![]
+);
+test_criterion!(
+    proximity_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Proximity],
+    vec![]
+);
 test_criterion!(
     asc_allow_typo,
     DISALLOW_OPTIONAL_WORDS,
     ALLOW_TYPOS,
-    vec![Asc(S("asc_desc_rank"))]
+    vec![Asc(S("asc_desc_rank"))],
+    vec![]
 );
 test_criterion!(
     asc_disallow_typo,
     DISALLOW_OPTIONAL_WORDS,
     DISALLOW_TYPOS,
-    vec![Asc(S("asc_desc_rank"))]
+    vec![Asc(S("asc_desc_rank"))],
+    vec![]
 );
 test_criterion!(
     desc_allow_typo,
     DISALLOW_OPTIONAL_WORDS,
     ALLOW_TYPOS,
-    vec![Desc(S("asc_desc_rank"))]
+    vec![Desc(S("asc_desc_rank"))],
+    vec![]
 );
 test_criterion!(
     desc_disallow_typo,
     DISALLOW_OPTIONAL_WORDS,
     DISALLOW_TYPOS,
-    vec![Desc(S("asc_desc_rank"))]
+    vec![Desc(S("asc_desc_rank"))],
+    vec![]
 );
 test_criterion!(
     asc_unexisting_field_allow_typo,
     DISALLOW_OPTIONAL_WORDS,
     ALLOW_TYPOS,
-    vec![Asc(S("unexisting_field"))]
+    vec![Asc(S("unexisting_field"))],
+    vec![]
 );
 test_criterion!(
     asc_unexisting_field_disallow_typo,
     DISALLOW_OPTIONAL_WORDS,
     DISALLOW_TYPOS,
-    vec![Asc(S("unexisting_field"))]
+    vec![Asc(S("unexisting_field"))],
+    vec![]
 );
 test_criterion!(
     desc_unexisting_field_allow_typo,
     DISALLOW_OPTIONAL_WORDS,
     ALLOW_TYPOS,
-    vec![Desc(S("unexisting_field"))]
+    vec![Desc(S("unexisting_field"))],
+    vec![]
 );
 test_criterion!(
     desc_unexisting_field_disallow_typo,
     DISALLOW_OPTIONAL_WORDS,
     DISALLOW_TYPOS,
-    vec![Desc(S("unexisting_field"))]
+    vec![Desc(S("unexisting_field"))],
+    vec![]
+);
+test_criterion!(empty_sort_by_allow_typo, DISALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, vec![Sort], vec![]);
+test_criterion!(
+    empty_sort_by_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Sort],
+    vec![]
+);
+test_criterion!(
+    sort_by_asc_allow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    ALLOW_TYPOS,
+    vec![Sort],
+    vec![AscDesc::Asc(S("tag"))]
+);
+test_criterion!(
+    sort_by_asc_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Sort],
+    vec![AscDesc::Asc(S("tag"))]
+);
+test_criterion!(
+    sort_by_desc_allow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    ALLOW_TYPOS,
+    vec![Sort],
+    vec![AscDesc::Desc(S("tag"))]
+);
+test_criterion!(
+    sort_by_desc_disallow_typo,
+    DISALLOW_OPTIONAL_WORDS,
+    DISALLOW_TYPOS,
+    vec![Sort],
+    vec![AscDesc::Desc(S("tag"))]
 );
 test_criterion!(
     default_criteria_order,
     ALLOW_OPTIONAL_WORDS,
     ALLOW_TYPOS,
-    vec![Words, Typo, Proximity, Attribute, Exactness]
+    vec![Words, Typo, Proximity, Attribute, Exactness],
+    vec![]
 );
 
 #[test]
@@ -262,7 +348,7 @@ fn criteria_mixup() {
         let SearchResult { documents_ids, .. } = search.execute().unwrap();
 
         let expected_external_ids: Vec<_> =
-            search::expected_order(&criteria, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS)
+            search::expected_order(&criteria, ALLOW_OPTIONAL_WORDS, ALLOW_TYPOS, &[])
                 .into_iter()
                 .map(|d| d.id)
                 .collect();