diff --git a/milli/src/documents/builder.rs b/milli/src/documents/builder.rs
index ba1319eff..98213edd7 100644
--- a/milli/src/documents/builder.rs
+++ b/milli/src/documents/builder.rs
@@ -1,9 +1,13 @@
+use std::collections::BTreeMap;
 use std::io;
 
 use byteorder::{BigEndian, WriteBytesExt};
-use serde::ser::Serialize;
+use serde::Deserializer;
+use serde_json::Value;
 
-use super::serde::DocumentSerializer;
+use crate::FieldId;
+
+use super::serde::DocumentVisitor;
 use super::{ByteCounter, DocumentsBatchIndex, DocumentsMetadata, Error};
 
 /// The `DocumentsBatchBuilder` provides a way to build a documents batch in the intermediary
@@ -24,7 +28,12 @@ use super::{ByteCounter, DocumentsBatchIndex, DocumentsMetadata, Error};
 /// builder.finish().unwrap();
 /// ```
 pub struct DocumentBatchBuilder<W> {
-    serializer: DocumentSerializer<W>,
+    inner: ByteCounter<W>,
+    index: DocumentsBatchIndex,
+    obkv_buffer: Vec<u8>,
+    value_buffer: Vec<u8>,
+    values: BTreeMap<FieldId, Value>,
+    count: usize,
 }
 
 impl<W: io::Write + io::Seek> DocumentBatchBuilder<W> {
@@ -34,27 +43,33 @@ impl<W: io::Write + io::Seek> DocumentBatchBuilder<W> {
         // add space to write the offset of the metadata at the end of the writer
         writer.write_u64::<BigEndian>(0)?;
 
-        let serializer =
-            DocumentSerializer { writer, buffer: Vec::new(), index, count: 0, allow_seq: true };
+        let this = Self {
+            inner: writer,
+            index,
+            obkv_buffer: Vec::new(),
+            value_buffer: Vec::new(),
+            values: BTreeMap::new(),
+            count: 0,
+        };
 
-        Ok(Self { serializer })
+        Ok(this)
     }
 
     /// Returns the number of documents that have been written to the builder.
     pub fn len(&self) -> usize {
-        self.serializer.count
+        self.count
     }
 
     /// This method must be called after the document addition is terminated. It will put the
     /// metadata at the end of the file, and write the metadata offset at the beginning on the
     /// file.
     pub fn finish(self) -> Result<(), Error> {
-        let DocumentSerializer {
-            writer: ByteCounter { mut writer, count: offset },
+        let Self {
+            inner: ByteCounter { mut writer, count: offset },
             index,
             count,
             ..
-        } = self.serializer;
+        } = self;
 
         let meta = DocumentsMetadata { count, index };
 
@@ -68,13 +83,106 @@ impl<W: io::Write + io::Seek> DocumentBatchBuilder<W> {
         Ok(())
     }
 
-    /// Adds documents to the builder.
-    ///
-    /// The internal index is updated with the fields found
-    /// in the documents. Document must either be a map or a sequences of map, anything else will
-    /// fail.
-    pub fn add_documents<T: Serialize>(&mut self, document: T) -> Result<(), Error> {
-        document.serialize(&mut self.serializer)?;
+
+    /// Extends the builder with json documents from a reader.
+    pub fn extend_from_json<R: io::Read>(&mut self, reader: R) -> Result<(), Error> {
+        let mut de = serde_json::Deserializer::from_reader(reader);
+
+        let mut visitor = DocumentVisitor {
+            inner: &mut self.inner,
+            index: &mut self.index,
+            obkv_buffer: &mut self.obkv_buffer,
+            value_buffer: &mut self.value_buffer,
+            values: &mut self.values,
+            count: &mut self.count,
+        };
+
+        de.deserialize_any(&mut visitor).unwrap();
+
         Ok(())
     }
 }
+
+#[cfg(test)]
+mod test {
+    use std::io::Cursor;
+
+    use crate::documents::DocumentBatchReader;
+
+    use super::*;
+
+    #[test]
+    fn add_single_documents_json() {
+        let mut cursor = Cursor::new(Vec::new());
+        let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
+
+        let json = serde_json::json!({
+            "id": 1,
+            "field": "hello!",
+        });
+
+        builder.extend_from_json(Cursor::new(serde_json::to_vec(&json).unwrap())).unwrap();
+
+        let json = serde_json::json!({
+            "blabla": false,
+            "field": "hello!",
+            "id": 1,
+        });
+
+        builder.extend_from_json(Cursor::new(serde_json::to_vec(&json).unwrap())).unwrap();
+
+        assert_eq!(builder.len(), 2);
+
+        builder.finish().unwrap();
+
+        cursor.set_position(0);
+
+        let mut reader = DocumentBatchReader::from_reader(cursor).unwrap();
+
+        let (index, document) = reader.next_document_with_index().unwrap().unwrap();
+        assert_eq!(index.len(), 3);
+        assert_eq!(document.iter().count(), 2);
+
+        let (index, document) = reader.next_document_with_index().unwrap().unwrap();
+        assert_eq!(index.len(), 3);
+        assert_eq!(document.iter().count(), 3);
+
+        assert!(reader.next_document_with_index().unwrap().is_none());
+    }
+
+    #[test]
+    fn add_documents_seq_json() {
+        let mut cursor = Cursor::new(Vec::new());
+        let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
+
+        let json = serde_json::json!([{
+            "id": 1,
+            "field": "hello!",
+        },{
+            "blabla": false,
+            "field": "hello!",
+            "id": 1,
+        }
+        ]);
+
+        builder.extend_from_json(Cursor::new(serde_json::to_vec(&json).unwrap())).unwrap();
+
+        assert_eq!(builder.len(), 2);
+
+        builder.finish().unwrap();
+
+        cursor.set_position(0);
+
+        let mut reader = DocumentBatchReader::from_reader(cursor).unwrap();
+
+        let (index, document) = reader.next_document_with_index().unwrap().unwrap();
+        assert_eq!(index.len(), 3);
+        assert_eq!(document.iter().count(), 2);
+
+        let (index, document) = reader.next_document_with_index().unwrap().unwrap();
+        assert_eq!(index.len(), 3);
+        assert_eq!(document.iter().count(), 3);
+
+        assert!(reader.next_document_with_index().unwrap().is_none());
+    }
+}
diff --git a/milli/src/documents/mod.rs b/milli/src/documents/mod.rs
index f79c210fe..ce0539c24 100644
--- a/milli/src/documents/mod.rs
+++ b/milli/src/documents/mod.rs
@@ -92,7 +92,8 @@ macro_rules! documents {
         let documents = serde_json::json!($data);
         let mut writer = std::io::Cursor::new(Vec::new());
         let mut builder = crate::documents::DocumentBatchBuilder::new(&mut writer).unwrap();
-        builder.add_documents(documents).unwrap();
+        let documents = serde_json::to_vec(&documents).unwrap();
+        builder.extend_from_json(std::io::Cursor::new(documents)).unwrap();
         builder.finish().unwrap();
 
         writer.set_position(0);
@@ -124,7 +125,8 @@ mod test {
 
         let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
 
-        builder.add_documents(json).unwrap();
+        todo!();
+        //builder.add_documents(json).unwrap();
 
         builder.finish().unwrap();
 
@@ -153,8 +155,9 @@ mod test {
 
         let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
 
-        builder.add_documents(doc1).unwrap();
-        builder.add_documents(doc2).unwrap();
+        todo!();
+        //builder.add_documents(doc1).unwrap();
+        //builder.add_documents(doc2).unwrap();
 
         builder.finish().unwrap();
 
@@ -182,7 +185,8 @@ mod test {
 
         let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
 
-        builder.add_documents(docs).unwrap();
+        todo!();
+        //builder.add_documents(docs).unwrap();
 
         builder.finish().unwrap();
 
@@ -210,11 +214,13 @@ mod test {
             { "tata": "hello" },
         ]]);
 
-        assert!(builder.add_documents(docs).is_err());
+        todo!();
+        //assert!(builder.add_documents(docs).is_err());
 
         let docs = json!("hello");
 
-        assert!(builder.add_documents(docs).is_err());
+        todo!();
+        //assert!(builder.add_documents(docs).is_err());
     }
 
     #[test]
diff --git a/milli/src/documents/serde.rs b/milli/src/documents/serde.rs
index 036ec246a..0d02fff6c 100644
--- a/milli/src/documents/serde.rs
+++ b/milli/src/documents/serde.rs
@@ -1,474 +1,128 @@
 use std::collections::BTreeMap;
-use std::convert::TryInto;
 use std::io::Cursor;
-use std::{fmt, io};
+use std::io::Write;
+use std::fmt;
 
-use byteorder::{BigEndian, WriteBytesExt};
-use obkv::KvWriter;
-use serde::ser::{Impossible, Serialize, SerializeMap, SerializeSeq, Serializer};
+use byteorder::WriteBytesExt;
+use serde::Deserialize;
+use serde::de::DeserializeSeed;
+use serde::de::MapAccess;
+use serde::de::SeqAccess;
+use serde::de::Visitor;
 use serde_json::Value;
 
-use super::{ByteCounter, DocumentsBatchIndex, Error};
+use super::{ByteCounter, DocumentsBatchIndex};
 use crate::FieldId;
 
-pub struct DocumentSerializer<W> {
-    pub writer: ByteCounter<W>,
-    pub buffer: Vec<u8>,
-    pub index: DocumentsBatchIndex,
-    pub count: usize,
-    pub allow_seq: bool,
-}
+struct FieldIdResolver<'a>(&'a mut DocumentsBatchIndex);
 
-impl<'a, W: io::Write> Serializer for &'a mut DocumentSerializer<W> {
-    type Ok = ();
+impl<'a, 'de> DeserializeSeed<'de> for FieldIdResolver<'a> {
+    type Value = FieldId;
 
-    type Error = Error;
-
-    type SerializeSeq = SeqSerializer<'a, W>;
-    type SerializeTuple = Impossible<(), Self::Error>;
-    type SerializeTupleStruct = Impossible<(), Self::Error>;
-    type SerializeTupleVariant = Impossible<(), Self::Error>;
-    type SerializeMap = MapSerializer<'a, &'a mut ByteCounter<W>>;
-    type SerializeStruct = Impossible<(), Self::Error>;
-    type SerializeStructVariant = Impossible<(), Self::Error>;
-    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
-        self.buffer.clear();
-        let cursor = io::Cursor::new(&mut self.buffer);
-        self.count += 1;
-        let map_serializer = MapSerializer {
-            map: KvWriter::new(cursor),
-            index: &mut self.index,
-            writer: &mut self.writer,
-            mapped_documents: BTreeMap::new(),
-        };
-
-        Ok(map_serializer)
-    }
-
-    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
-        if self.allow_seq {
-            // Only allow sequence of documents of depth 1.
-            self.allow_seq = false;
-            Ok(SeqSerializer { serializer: self })
-        } else {
-            Err(Error::InvalidDocumentFormat)
-        }
-    }
-
-    fn serialize_bool(self, _v: bool) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i8(self, _v: i8) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i16(self, _v: i16) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i32(self, _v: i32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i64(self, _v: i64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u8(self, _v: u8) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u16(self, _v: u16) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u32(self, _v: u32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u64(self, _v: u64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_f32(self, _v: f32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_f64(self, _v: f64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_char(self, _v: char) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_str(self, _v: &str) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<Self::Ok, Self::Error>
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
     where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-    ) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_newtype_struct<T: ?Sized>(
-        self,
-        _name: &'static str,
-        _value: &T,
-    ) -> Result<Self::Ok, Self::Error>
-    where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_newtype_variant<T: ?Sized>(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _value: &T,
-    ) -> Result<Self::Ok, Self::Error>
-    where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple_struct(
-        self,
-        _name: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_struct(
-        self,
-        _name: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeStruct, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_struct_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeStructVariant, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
+        D: serde::Deserializer<'de> {
+            deserializer.deserialize_str(self)
     }
 }
 
-pub struct SeqSerializer<'a, W> {
-    serializer: &'a mut DocumentSerializer<W>,
+impl<'a, 'de> Visitor<'de> for FieldIdResolver<'a> {
+    type Value = FieldId;
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error, {
+            let field_id = match self.0.get_by_right(v) {
+                Some(field_id) => *field_id,
+                None => {
+                    let field_id = self.0.len() as FieldId;
+                    self.0.insert(field_id, v.to_string());
+                    field_id
+                }
+            };
+
+            Ok(field_id)
+    }
+
+    fn expecting(&self, _formatter: &mut fmt::Formatter) -> fmt::Result {
+        todo!()
+    }
 }
 
-impl<'a, W: io::Write> SerializeSeq for SeqSerializer<'a, W> {
-    type Ok = ();
-    type Error = Error;
+struct ValueDeserializer;
 
-    fn serialize_element<T: ?Sized>(&mut self, value: &T) -> Result<(), Self::Error>
+impl<'de> DeserializeSeed<'de> for ValueDeserializer {
+    type Value = serde_json::Value;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
     where
-        T: Serialize,
+        D: serde::Deserializer<'de> {
+            serde_json::Value::deserialize(deserializer)
+    }
+}
+
+pub struct DocumentVisitor<'a, W> {
+    pub inner: &'a mut ByteCounter<W>,
+    pub index: &'a mut DocumentsBatchIndex,
+    pub obkv_buffer: &'a mut Vec<u8>,
+    pub value_buffer: &'a mut Vec<u8>,
+    pub values: &'a mut BTreeMap<FieldId, Value>,
+    pub count: &'a mut usize,
+}
+
+impl<'a, 'de, W: Write> Visitor<'de> for &mut DocumentVisitor<'a, W> {
+    /// This Visitor value is nothing, since it write the value to a file.
+    type Value = ();
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
     {
-        value.serialize(&mut *self.serializer)?;
+        while let Some(_) = seq.next_element_seed(&mut *self)? { }
+
         Ok(())
     }
 
-    fn end(self) -> Result<Self::Ok, Self::Error> {
-        Ok(())
-    }
-}
-
-pub struct MapSerializer<'a, W> {
-    map: KvWriter<io::Cursor<&'a mut Vec<u8>>, FieldId>,
-    index: &'a mut DocumentsBatchIndex,
-    writer: W,
-    mapped_documents: BTreeMap<FieldId, Value>,
-}
-
-/// This implementation of SerializeMap uses serilialize_entry instead of seriliaze_key and
-/// serialize_value, therefore these to methods remain unimplemented.
-impl<'a, W: io::Write> SerializeMap for MapSerializer<'a, W> {
-    type Ok = ();
-    type Error = Error;
-
-    fn serialize_key<T: ?Sized + Serialize>(&mut self, _key: &T) -> Result<(), Self::Error> {
-        unreachable!()
-    }
-
-    fn serialize_value<T: ?Sized>(&mut self, _value: &T) -> Result<(), Self::Error> {
-        unreachable!()
-    }
-
-    fn end(mut self) -> Result<Self::Ok, Self::Error> {
-        let mut buf = Vec::new();
-        for (key, value) in self.mapped_documents {
-            buf.clear();
-            let mut cursor = Cursor::new(&mut buf);
-            serde_json::to_writer(&mut cursor, &value).map_err(Error::JsonError)?;
-            self.map.insert(key, cursor.into_inner()).map_err(Error::Io)?;
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        while let Some((key, value)) = map.next_entry_seed(FieldIdResolver(&mut *self.index), ValueDeserializer).unwrap() {
+            self.values.insert(key, value);
         }
 
-        let data = self.map.into_inner().map_err(Error::Io)?.into_inner();
-        let data_len: u32 = data.len().try_into().map_err(|_| Error::DocumentTooLarge)?;
+        self.obkv_buffer.clear();
+        let mut obkv = obkv::KvWriter::new(Cursor::new(&mut *self.obkv_buffer));
+        for (key, value) in self.values.iter() {
+            self.value_buffer.clear();
+            // This is guaranteed to work
+            serde_json::to_writer(Cursor::new(&mut *self.value_buffer), value).unwrap();
+            obkv.insert(*key, &self.value_buffer).unwrap();
+        }
 
-        self.writer.write_u32::<BigEndian>(data_len).map_err(Error::Io)?;
-        self.writer.write_all(&data).map_err(Error::Io)?;
+        let reader = obkv.into_inner().unwrap().into_inner();
+
+        self.inner.write_u32::<byteorder::BigEndian>(reader.len() as u32).unwrap();
+        self.inner.write_all(reader).unwrap();
+
+        *self.count += 1;
 
         Ok(())
     }
 
-    fn serialize_entry<K: ?Sized, V: ?Sized>(
-        &mut self,
-        key: &K,
-        value: &V,
-    ) -> Result<(), Self::Error>
-    where
-        K: Serialize,
-        V: Serialize,
-    {
-        let field_serializer = FieldSerializer { index: &mut self.index };
-        let field_id: FieldId = key.serialize(field_serializer)?;
-
-        let value = serde_json::to_value(value).map_err(Error::JsonError)?;
-
-        self.mapped_documents.insert(field_id, value);
-
-        Ok(())
+    fn expecting(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "a documents, or a sequence of documents.")
     }
 }
 
-struct FieldSerializer<'a> {
-    index: &'a mut DocumentsBatchIndex,
-}
+impl<'a, 'de, W> DeserializeSeed<'de> for &mut DocumentVisitor<'a, W>
+where W: Write,
+{
+    type Value = ();
 
-impl<'a> serde::Serializer for FieldSerializer<'a> {
-    type Ok = FieldId;
-
-    type Error = Error;
-
-    type SerializeSeq = Impossible<FieldId, Self::Error>;
-    type SerializeTuple = Impossible<FieldId, Self::Error>;
-    type SerializeTupleStruct = Impossible<FieldId, Self::Error>;
-    type SerializeTupleVariant = Impossible<FieldId, Self::Error>;
-    type SerializeMap = Impossible<FieldId, Self::Error>;
-    type SerializeStruct = Impossible<FieldId, Self::Error>;
-    type SerializeStructVariant = Impossible<FieldId, Self::Error>;
-
-    fn serialize_str(self, ws: &str) -> Result<Self::Ok, Self::Error> {
-        let field_id = match self.index.get_by_right(ws) {
-            Some(field_id) => *field_id,
-            None => {
-                let field_id = self.index.len() as FieldId;
-                self.index.insert(field_id, ws.to_string());
-                field_id
-            }
-        };
-
-        Ok(field_id)
-    }
-
-    fn serialize_bool(self, _v: bool) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i8(self, _v: i8) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i16(self, _v: i16) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i32(self, _v: i32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_i64(self, _v: i64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u8(self, _v: u8) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u16(self, _v: u16) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u32(self, _v: u32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_u64(self, _v: u64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_f32(self, _v: f32) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_f64(self, _v: f64) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_char(self, _v: char) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<Self::Ok, Self::Error>
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
     where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_unit_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-    ) -> Result<Self::Ok, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_newtype_struct<T: ?Sized>(
-        self,
-        _name: &'static str,
-        _value: &T,
-    ) -> Result<Self::Ok, Self::Error>
-    where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_newtype_variant<T: ?Sized>(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _value: &T,
-    ) -> Result<Self::Ok, Self::Error>
-    where
-        T: Serialize,
-    {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple_struct(
-        self,
-        _name: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeTupleStruct, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_tuple_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeTupleVariant, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_struct(
-        self,
-        _name: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeStruct, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-
-    fn serialize_struct_variant(
-        self,
-        _name: &'static str,
-        _variant_index: u32,
-        _variant: &'static str,
-        _len: usize,
-    ) -> Result<Self::SerializeStructVariant, Self::Error> {
-        Err(Error::InvalidDocumentFormat)
-    }
-}
-
-impl serde::ser::Error for Error {
-    fn custom<T: fmt::Display>(msg: T) -> Self {
-        Error::Custom(msg.to_string())
+        D: serde::Deserializer<'de> {
+            deserializer.deserialize_map(self)
     }
 }
diff --git a/milli/src/search/distinct/mod.rs b/milli/src/search/distinct/mod.rs
index deb51a053..5639c53fa 100644
--- a/milli/src/search/distinct/mod.rs
+++ b/milli/src/search/distinct/mod.rs
@@ -68,7 +68,8 @@ mod test {
                 "txts": sample_txts[..(rng.gen_range(0..3))],
                 "cat-ints": sample_ints[..(rng.gen_range(0..3))],
             });
-            builder.add_documents(doc).unwrap();
+            todo!()
+            //builder.add_documents(doc).unwrap();
         }
 
         builder.finish().unwrap();
diff --git a/milli/src/update/index_documents/mod.rs b/milli/src/update/index_documents/mod.rs
index 92bcab0e9..58e21a615 100644
--- a/milli/src/update/index_documents/mod.rs
+++ b/milli/src/update/index_documents/mod.rs
@@ -877,7 +877,8 @@ mod tests {
         let mut cursor = Cursor::new(Vec::new());
 
         let mut builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
-        builder.add_documents(big_object).unwrap();
+        todo!();
+        //builder.add_documents(big_object).unwrap();
         builder.finish().unwrap();
         cursor.set_position(0);
         let content = DocumentBatchReader::from_reader(cursor).unwrap();
diff --git a/milli/tests/search/mod.rs b/milli/tests/search/mod.rs
index cda0da617..d62b8ec31 100644
--- a/milli/tests/search/mod.rs
+++ b/milli/tests/search/mod.rs
@@ -61,9 +61,10 @@ pub fn setup_search_index_with_criteria(criteria: &[Criterion]) -> Index {
     let mut cursor = Cursor::new(Vec::new());
     let mut documents_builder = DocumentBatchBuilder::new(&mut cursor).unwrap();
     let reader = Cursor::new(CONTENT.as_bytes());
-    for doc in serde_json::Deserializer::from_reader(reader).into_iter::<serde_json::Value>() {
-        documents_builder.add_documents(doc.unwrap()).unwrap();
-    }
+    todo!();
+    //for doc in serde_json::Deserializer::from_reader(reader).into_iter::<serde_json::Value>() {
+        //documents_builder.add_documents(doc.unwrap()).unwrap();
+    //}
     documents_builder.finish().unwrap();
 
     cursor.set_position(0);
diff --git a/milli/tests/search/query_criteria.rs b/milli/tests/search/query_criteria.rs
index f3b04c4fa..3fb36b1d5 100644
--- a/milli/tests/search/query_criteria.rs
+++ b/milli/tests/search/query_criteria.rs
@@ -409,7 +409,8 @@ fn criteria_ascdesc() {
             "age": age,
         });
 
-        batch_builder.add_documents(json).unwrap();
+        todo!();
+        //batch_builder.add_documents(json).unwrap();
     });
 
     batch_builder.finish().unwrap();