diff --git a/examples/create-database.rs b/examples/create-database.rs
index e7a8e72e4..e1f1cb0b5 100644
--- a/examples/create-database.rs
+++ b/examples/create-database.rs
@@ -1,16 +1,13 @@
-use std::collections::hash_map::DefaultHasher;
 use std::path::{Path, PathBuf};
-use std::hash::{Hash, Hasher};
 use std::error::Error;
 
 use serde_derive::{Serialize, Deserialize};
 use structopt::StructOpt;
 
 use meilidb::database::schema::{Schema, SchemaBuilder, STORED, INDEXED};
-use meilidb::database::update::PositiveUpdateBuilder;
+use meilidb::database::PositiveUpdateBuilder;
 use meilidb::tokenizer::DefaultBuilder;
 use meilidb::database::Database;
-use meilidb::DocumentId;
 
 #[derive(Debug, StructOpt)]
 pub struct Opt {
@@ -31,14 +28,8 @@ struct Document<'a> {
     image: &'a str,
 }
 
-fn calculate_hash<T: Hash>(t: &T) -> u64 {
-    let mut s = DefaultHasher::new();
-    t.hash(&mut s);
-    s.finish()
-}
-
 fn create_schema() -> Schema {
-    let mut schema = SchemaBuilder::new();
+    let mut schema = SchemaBuilder::with_identifier("id");
     schema.new_attribute("id", STORED);
     schema.new_attribute("title", STORED | INDEXED);
     schema.new_attribute("description", STORED | INDEXED);
@@ -68,8 +59,7 @@ fn index(schema: Schema, database_path: &Path, csv_data_path: &Path) -> Result<D
             }
         };
 
-        let document_id = DocumentId(calculate_hash(&document.id));
-        update.update(document_id, &document).unwrap();
+        update.update(&document).unwrap();
     }
 
     let mut update = update.build()?;
diff --git a/examples/query-database.rs b/examples/query-database.rs
index 9b6a067cd..e6fb6ee93 100644
--- a/examples/query-database.rs
+++ b/examples/query-database.rs
@@ -88,7 +88,7 @@ fn main() -> Result<(), Box<Error>> {
 
         let number_of_documents = documents.len();
         for doc in documents {
-            match view.retrieve_document::<Document>(doc.id) {
+            match view.document_by_id::<Document>(doc.id) {
                 Ok(document) => {
 
                     print!("title: ");
diff --git a/src/database/database.rs b/src/database/database.rs
new file mode 100644
index 000000000..5db8d3ac7
--- /dev/null
+++ b/src/database/database.rs
@@ -0,0 +1,233 @@
+use std::sync::{Arc, Mutex, RwLock, RwLockReadGuard};
+use std::error::Error;
+use std::path::Path;
+
+use rocksdb::rocksdb_options::{DBOptions, IngestExternalFileOptions, ColumnFamilyOptions};
+use rocksdb::rocksdb::{Writable, Snapshot};
+use rocksdb::{DB, DBVector, MergeOperands};
+
+use crate::database::{DatabaseView, Update, Schema};
+use crate::database::{DATA_INDEX, DATA_SCHEMA};
+use crate::database::blob::{self, Blob};
+
+pub struct Database {
+    // DB is under a Mutex to sync update ingestions and separate DB update locking
+    // and DatabaseView acquiring locking in other words:
+    // "Block readers the minimum possible amount of time"
+    db: Mutex<Arc<DB>>,
+
+    // This view is updated each time the DB ingests an update
+    view: RwLock<DatabaseView<Arc<DB>>>,
+}
+
+impl Database {
+    pub fn create<P: AsRef<Path>>(path: P, schema: Schema) -> Result<Database, Box<Error>> {
+        let path = path.as_ref();
+        if path.exists() {
+            return Err(format!("File already exists at path: {}, cannot create database.",
+                                path.display()).into())
+        }
+
+        let path = path.to_string_lossy();
+        let mut opts = DBOptions::new();
+        opts.create_if_missing(true);
+        // opts.error_if_exists(true); // FIXME pull request that
+
+        let mut cf_opts = ColumnFamilyOptions::new();
+        cf_opts.add_merge_operator("data-index merge operator", merge_indexes);
+
+        let db = DB::open_cf(opts, &path, vec![("default", cf_opts)])?;
+
+        let mut schema_bytes = Vec::new();
+        schema.write_to(&mut schema_bytes)?;
+        db.put(DATA_SCHEMA, &schema_bytes)?;
+
+        let db = Arc::new(db);
+        let snapshot = Snapshot::new(db.clone());
+        let view = RwLock::new(DatabaseView::new(snapshot)?);
+
+        Ok(Database { db: Mutex::new(db), view })
+    }
+
+    pub fn open<P: AsRef<Path>>(path: P) -> Result<Database, Box<Error>> {
+        let path = path.as_ref().to_string_lossy();
+
+        let mut opts = DBOptions::new();
+        opts.create_if_missing(false);
+
+        let mut cf_opts = ColumnFamilyOptions::new();
+        cf_opts.add_merge_operator("data-index merge operator", merge_indexes);
+
+        let db = DB::open_cf(opts, &path, vec![("default", cf_opts)])?;
+
+        // FIXME create a generic function to do that !
+        let _schema = match db.get(DATA_SCHEMA)? {
+            Some(value) => Schema::read_from(&*value)?,
+            None => return Err(String::from("Database does not contain a schema").into()),
+        };
+
+        let db = Arc::new(db);
+        let snapshot = Snapshot::new(db.clone());
+        let view = RwLock::new(DatabaseView::new(snapshot)?);
+
+        Ok(Database { db: Mutex::new(db), view })
+    }
+
+    pub fn ingest_update_file(&self, update: Update) -> Result<(), Box<Error>> {
+        let snapshot = {
+            // We must have a mutex here to ensure that update ingestions and compactions
+            // are done atomatically and in the right order.
+            // This way update ingestions will block other update ingestions without blocking view
+            // creations while doing the "data-index" compaction
+            let db = match self.db.lock() {
+                Ok(db) => db,
+                Err(e) => return Err(e.to_string().into()),
+            };
+
+            let move_update = update.can_be_moved();
+            let path = update.into_path_buf();
+            let path = path.to_string_lossy();
+
+            let mut options = IngestExternalFileOptions::new();
+            options.move_files(move_update);
+
+            let cf_handle = db.cf_handle("default").expect("\"default\" column family not found");
+            db.ingest_external_file_optimized(&cf_handle, &options, &[&path])?;
+
+            // Compacting to trigger the merge operator only one time
+            // while ingesting the update and not each time searching
+            db.compact_range(Some(DATA_INDEX), Some(DATA_INDEX));
+
+            Snapshot::new(db.clone())
+        };
+
+        // Here we will block the view creation for the minimum amount of time:
+        // updating the DatabaseView itself with the new database snapshot
+        let view = DatabaseView::new(snapshot)?;
+        match self.view.write() {
+            Ok(mut lock) => *lock = view,
+            Err(e) => return Err(e.to_string().into()),
+        }
+
+        Ok(())
+    }
+
+    pub fn get(&self, key: &[u8]) -> Result<Option<DBVector>, Box<Error>> {
+        self.view().get(key)
+    }
+
+    pub fn flush(&self) -> Result<(), Box<Error>> {
+        match self.db.lock() {
+            Ok(db) => Ok(db.flush(true)?),
+            Err(e) => Err(e.to_string().into()),
+        }
+    }
+
+    pub fn view(&self) -> RwLockReadGuard<DatabaseView<Arc<DB>>> {
+        self.view.read().unwrap()
+    }
+}
+
+fn merge_indexes(key: &[u8], existing_value: Option<&[u8]>, operands: &mut MergeOperands) -> Vec<u8> {
+    if key != DATA_INDEX {
+        panic!("The merge operator only supports \"data-index\" merging")
+    }
+
+    let capacity = {
+        let remaining = operands.size_hint().0;
+        let already_exist = usize::from(existing_value.is_some());
+        remaining + already_exist
+    };
+
+    let mut op = blob::OpBuilder::with_capacity(capacity);
+    if let Some(existing_value) = existing_value {
+        let blob = bincode::deserialize(existing_value).expect("BUG: could not deserialize data-index");
+        op.push(Blob::Positive(blob));
+    }
+
+    for bytes in operands {
+        let blob = bincode::deserialize(bytes).expect("BUG: could not deserialize blob");
+        op.push(blob);
+    }
+
+    let blob = op.merge().expect("BUG: could not merge blobs");
+    bincode::serialize(&blob).expect("BUG: could not serialize merged blob")
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::error::Error;
+
+    use serde_derive::{Serialize, Deserialize};
+    use tempfile::tempdir;
+
+    use crate::tokenizer::DefaultBuilder;
+    use crate::database::update::PositiveUpdateBuilder;
+    use crate::database::schema::{SchemaBuilder, STORED, INDEXED};
+
+    #[test]
+    fn ingest_update_file() -> Result<(), Box<Error>> {
+        let dir = tempdir()?;
+
+        let rocksdb_path = dir.path().join("rocksdb.rdb");
+
+        #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
+        struct SimpleDoc {
+            id: u64,
+            title: String,
+            description: String,
+            timestamp: u64,
+        }
+
+        let schema = {
+            let mut builder = SchemaBuilder::with_identifier("id");
+            builder.new_attribute("id", STORED);
+            builder.new_attribute("title", STORED | INDEXED);
+            builder.new_attribute("description", STORED | INDEXED);
+            builder.new_attribute("timestamp", STORED);
+            builder.build()
+        };
+
+        let database = Database::create(&rocksdb_path, schema.clone())?;
+        let tokenizer_builder = DefaultBuilder::new();
+
+        let update_path = dir.path().join("update.sst");
+
+        let doc0 = SimpleDoc {
+            id: 0,
+            title: String::from("I am a title"),
+            description: String::from("I am a description"),
+            timestamp: 1234567,
+        };
+        let doc1 = SimpleDoc {
+            id: 1,
+            title: String::from("I am the second title"),
+            description: String::from("I am the second description"),
+            timestamp: 7654321,
+        };
+
+        let docid0;
+        let docid1;
+        let mut update = {
+            let mut builder = PositiveUpdateBuilder::new(update_path, schema, tokenizer_builder);
+
+            docid0 = builder.update(&doc0).unwrap();
+            docid1 = builder.update(&doc1).unwrap();
+
+            builder.build()?
+        };
+
+        update.set_move(true);
+        database.ingest_update_file(update)?;
+        let view = database.view();
+
+        let de_doc0: SimpleDoc = view.document_by_id(docid0)?;
+        let de_doc1: SimpleDoc = view.document_by_id(docid1)?;
+
+        assert_eq!(doc0, de_doc0);
+        assert_eq!(doc1, de_doc1);
+
+        Ok(dir.close()?)
+    }
+}
diff --git a/src/database/database_view.rs b/src/database/database_view.rs
index c8eed37c6..6e8d32a78 100644
--- a/src/database/database_view.rs
+++ b/src/database/database_view.rs
@@ -75,15 +75,14 @@ where D: Deref<Target=DB>
         QueryBuilder::new(self)
     }
 
-    // TODO create an enum error type
-    pub fn retrieve_document<T>(&self, id: DocumentId) -> Result<T, Box<Error>>
+    pub fn document_by_id<T>(&self, id: DocumentId) -> Result<T, Box<Error>>
     where T: DeserializeOwned
     {
         let mut deserializer = Deserializer::new(&self.snapshot, &self.schema, id);
         Ok(T::deserialize(&mut deserializer)?)
     }
 
-    pub fn retrieve_documents<T, I>(&self, ids: I) -> DocumentIter<D, T, I::IntoIter>
+    pub fn documents_by_id<T, I>(&self, ids: I) -> DocumentIter<D, T, I::IntoIter>
     where T: DeserializeOwned,
           I: IntoIterator<Item=DocumentId>,
     {
@@ -149,7 +148,7 @@ where D: Deref<Target=DB>,
 
     fn next(&mut self) -> Option<Self::Item> {
         match self.document_ids.next() {
-            Some(id) => Some(self.database_view.retrieve_document(id)),
+            Some(id) => Some(self.database_view.document_by_id(id)),
             None => None
         }
     }
@@ -168,7 +167,7 @@ where D: Deref<Target=DB>,
 {
     fn next_back(&mut self) -> Option<Self::Item> {
         match self.document_ids.next_back() {
-            Some(id) => Some(self.database_view.retrieve_document(id)),
+            Some(id) => Some(self.database_view.document_by_id(id)),
             None => None
         }
     }
diff --git a/src/database/mod.rs b/src/database/mod.rs
index 2351c658c..f3361ee35 100644
--- a/src/database/mod.rs
+++ b/src/database/mod.rs
@@ -1,30 +1,48 @@
-use std::sync::{Arc, Mutex, RwLock, RwLockReadGuard};
+use std::collections::hash_map::DefaultHasher;
+use std::hash::{Hash, Hasher};
 use std::error::Error;
-use std::path::Path;
 use std::ops::Deref;
 
-use rocksdb::rocksdb_options::{DBOptions, IngestExternalFileOptions, ColumnFamilyOptions};
-use rocksdb::rocksdb::{Writable, Snapshot};
-use rocksdb::{DB, DBVector, MergeOperands};
+use rocksdb::rocksdb::{DB, Snapshot};
 
+pub use self::update::{
+    Update, PositiveUpdateBuilder, NewState,
+    SerializerError, NegativeUpdateBuilder
+};
 pub use self::document_key::{DocumentKey, DocumentKeyAttr};
 pub use self::database_view::{DatabaseView, DocumentIter};
+pub use self::database::Database;
+pub use self::schema::Schema;
 use self::blob::positive::PositiveBlob;
-use self::update::Update;
-use self::schema::Schema;
-use self::blob::Blob;
-
-pub mod blob;
-pub mod schema;
-pub mod update;
-mod document_key;
-mod database_view;
-mod deserializer;
 
 const DATA_INDEX:  &[u8] = b"data-index";
 const DATA_SCHEMA: &[u8] = b"data-schema";
 
-pub fn retrieve_data_schema<D>(snapshot: &Snapshot<D>) -> Result<Schema, Box<Error>>
+macro_rules! forward_to_unserializable_type {
+    ($($ty:ident => $se_method:ident,)*) => {
+        $(
+            fn $se_method(self, _v: $ty) -> Result<Self::Ok, Self::Error> {
+                Err(SerializerError::UnserializableType { name: "$ty" })
+            }
+        )*
+    }
+}
+
+pub mod blob;
+pub mod schema;
+mod update;
+mod database;
+mod document_key;
+mod database_view;
+mod deserializer;
+
+fn calculate_hash<T: Hash>(t: &T) -> u64 {
+    let mut s = DefaultHasher::new();
+    t.hash(&mut s);
+    s.finish()
+}
+
+fn retrieve_data_schema<D>(snapshot: &Snapshot<D>) -> Result<Schema, Box<Error>>
 where D: Deref<Target=DB>
 {
     match snapshot.get(DATA_SCHEMA)? {
@@ -33,7 +51,7 @@ where D: Deref<Target=DB>
     }
 }
 
-pub fn retrieve_data_index<D>(snapshot: &Snapshot<D>) -> Result<PositiveBlob, Box<Error>>
+fn retrieve_data_index<D>(snapshot: &Snapshot<D>) -> Result<PositiveBlob, Box<Error>>
 where D: Deref<Target=DB>
 {
     match snapshot.get(DATA_INDEX)? {
@@ -41,220 +59,3 @@ where D: Deref<Target=DB>
         None => Ok(PositiveBlob::default()),
     }
 }
-
-pub struct Database {
-    // DB is under a Mutex to sync update ingestions and separate DB update locking
-    // and DatabaseView acquiring locking in other words:
-    // "Block readers the minimum possible amount of time"
-    db: Mutex<Arc<DB>>,
-
-    // This view is updated each time the DB ingests an update
-    view: RwLock<DatabaseView<Arc<DB>>>,
-}
-
-impl Database {
-    pub fn create<P: AsRef<Path>>(path: P, schema: Schema) -> Result<Database, Box<Error>> {
-        let path = path.as_ref();
-        if path.exists() {
-            return Err(format!("File already exists at path: {}, cannot create database.",
-                                path.display()).into())
-        }
-
-        let path = path.to_string_lossy();
-        let mut opts = DBOptions::new();
-        opts.create_if_missing(true);
-        // opts.error_if_exists(true); // FIXME pull request that
-
-        let mut cf_opts = ColumnFamilyOptions::new();
-        cf_opts.add_merge_operator("data-index merge operator", merge_indexes);
-
-        let db = DB::open_cf(opts, &path, vec![("default", cf_opts)])?;
-
-        let mut schema_bytes = Vec::new();
-        schema.write_to(&mut schema_bytes)?;
-        db.put(DATA_SCHEMA, &schema_bytes)?;
-
-        let db = Arc::new(db);
-        let snapshot = Snapshot::new(db.clone());
-        let view = RwLock::new(DatabaseView::new(snapshot)?);
-
-        Ok(Database { db: Mutex::new(db), view })
-    }
-
-    pub fn open<P: AsRef<Path>>(path: P) -> Result<Database, Box<Error>> {
-        let path = path.as_ref().to_string_lossy();
-
-        let mut opts = DBOptions::new();
-        opts.create_if_missing(false);
-
-        let mut cf_opts = ColumnFamilyOptions::new();
-        cf_opts.add_merge_operator("data-index merge operator", merge_indexes);
-
-        let db = DB::open_cf(opts, &path, vec![("default", cf_opts)])?;
-
-        // FIXME create a generic function to do that !
-        let _schema = match db.get(DATA_SCHEMA)? {
-            Some(value) => Schema::read_from(&*value)?,
-            None => return Err(String::from("Database does not contain a schema").into()),
-        };
-
-        let db = Arc::new(db);
-        let snapshot = Snapshot::new(db.clone());
-        let view = RwLock::new(DatabaseView::new(snapshot)?);
-
-        Ok(Database { db: Mutex::new(db), view })
-    }
-
-    pub fn ingest_update_file(&self, update: Update) -> Result<(), Box<Error>> {
-        let snapshot = {
-            // We must have a mutex here to ensure that update ingestions and compactions
-            // are done atomatically and in the right order.
-            // This way update ingestions will block other update ingestions without blocking view
-            // creations while doing the "data-index" compaction
-            let db = match self.db.lock() {
-                Ok(db) => db,
-                Err(e) => return Err(e.to_string().into()),
-            };
-
-            let move_update = update.can_be_moved();
-            let path = update.into_path_buf();
-            let path = path.to_string_lossy();
-
-            let mut options = IngestExternalFileOptions::new();
-            options.move_files(move_update);
-
-            let cf_handle = db.cf_handle("default").expect("\"default\" column family not found");
-            db.ingest_external_file_optimized(&cf_handle, &options, &[&path])?;
-
-            // Compacting to trigger the merge operator only one time
-            // while ingesting the update and not each time searching
-            db.compact_range(Some(DATA_INDEX), Some(DATA_INDEX));
-
-            Snapshot::new(db.clone())
-        };
-
-        // Here we will block the view creation for the minimum amount of time:
-        // updating the DatabaseView itself with the new database snapshot
-        let view = DatabaseView::new(snapshot)?;
-        match self.view.write() {
-            Ok(mut lock) => *lock = view,
-            Err(e) => return Err(e.to_string().into()),
-        }
-
-        Ok(())
-    }
-
-    pub fn get(&self, key: &[u8]) -> Result<Option<DBVector>, Box<Error>> {
-        self.view().get(key)
-    }
-
-    pub fn flush(&self) -> Result<(), Box<Error>> {
-        match self.db.lock() {
-            Ok(db) => Ok(db.flush(true)?),
-            Err(e) => Err(e.to_string().into()),
-        }
-    }
-
-    pub fn view(&self) -> RwLockReadGuard<DatabaseView<Arc<DB>>> {
-        self.view.read().unwrap()
-    }
-}
-
-fn merge_indexes(key: &[u8], existing_value: Option<&[u8]>, operands: &mut MergeOperands) -> Vec<u8> {
-    if key != DATA_INDEX {
-        panic!("The merge operator only supports \"data-index\" merging")
-    }
-
-    let capacity = {
-        let remaining = operands.size_hint().0;
-        let already_exist = usize::from(existing_value.is_some());
-        remaining + already_exist
-    };
-
-    let mut op = blob::OpBuilder::with_capacity(capacity);
-    if let Some(existing_value) = existing_value {
-        let blob = bincode::deserialize(existing_value).expect("BUG: could not deserialize data-index");
-        op.push(Blob::Positive(blob));
-    }
-
-    for bytes in operands {
-        let blob = bincode::deserialize(bytes).expect("BUG: could not deserialize blob");
-        op.push(blob);
-    }
-
-    let blob = op.merge().expect("BUG: could not merge blobs");
-    bincode::serialize(&blob).expect("BUG: could not serialize merged blob")
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-    use std::error::Error;
-
-    use serde_derive::{Serialize, Deserialize};
-    use tempfile::tempdir;
-
-    use crate::DocumentId;
-    use crate::tokenizer::DefaultBuilder;
-    use crate::database::update::PositiveUpdateBuilder;
-    use crate::database::schema::{SchemaBuilder, STORED, INDEXED};
-
-    #[test]
-    fn ingest_update_file() -> Result<(), Box<Error>> {
-        let dir = tempdir()?;
-
-        let rocksdb_path = dir.path().join("rocksdb.rdb");
-
-        #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq)]
-        struct SimpleDoc {
-            title: String,
-            description: String,
-            timestamp: u64,
-        }
-
-        let schema = {
-            let mut builder = SchemaBuilder::new();
-            builder.new_attribute("title", STORED | INDEXED);
-            builder.new_attribute("description", STORED | INDEXED);
-            builder.new_attribute("timestamp", STORED);
-            builder.build()
-        };
-
-        let database = Database::create(&rocksdb_path, schema.clone())?;
-        let tokenizer_builder = DefaultBuilder::new();
-
-        let update_path = dir.path().join("update.sst");
-
-        let doc0 = SimpleDoc {
-            title: String::from("I am a title"),
-            description: String::from("I am a description"),
-            timestamp: 1234567,
-        };
-        let doc1 = SimpleDoc {
-            title: String::from("I am the second title"),
-            description: String::from("I am the second description"),
-            timestamp: 7654321,
-        };
-
-        let mut update = {
-            let mut builder = PositiveUpdateBuilder::new(update_path, schema, tokenizer_builder);
-
-            builder.update(DocumentId(0), &doc0).unwrap();
-            builder.update(DocumentId(1), &doc1).unwrap();
-
-            builder.build()?
-        };
-
-        update.set_move(true);
-        database.ingest_update_file(update)?;
-        let view = database.view();
-
-        let de_doc0: SimpleDoc = view.retrieve_document(DocumentId(0))?;
-        let de_doc1: SimpleDoc = view.retrieve_document(DocumentId(1))?;
-
-        assert_eq!(doc0, de_doc0);
-        assert_eq!(doc1, de_doc1);
-
-        Ok(dir.close()?)
-    }
-}
diff --git a/src/database/schema.rs b/src/database/schema.rs
index edb19ad79..0d02f342b 100644
--- a/src/database/schema.rs
+++ b/src/database/schema.rs
@@ -1,4 +1,6 @@
+use crate::database::update::SerializerError;
 use std::collections::{HashMap, BTreeMap};
+use crate::database::calculate_hash;
 use std::io::{Read, Write};
 use std::{fmt, u16};
 use std::path::Path;
@@ -7,8 +9,11 @@ use std::sync::Arc;
 use std::fs::File;
 
 use serde_derive::{Serialize, Deserialize};
+use serde::ser::{self, Serialize};
 use linked_hash_map::LinkedHashMap;
 
+use crate::DocumentId;
+
 pub const STORED: SchemaProps = SchemaProps { stored: true, indexed: false };
 pub const INDEXED: SchemaProps = SchemaProps { stored: false, indexed: true };
 
@@ -40,12 +45,16 @@ impl BitOr for SchemaProps {
 }
 
 pub struct SchemaBuilder {
+    identifier: String,
     attrs: LinkedHashMap<String, SchemaProps>,
 }
 
 impl SchemaBuilder {
-    pub fn new() -> SchemaBuilder {
-        SchemaBuilder { attrs: LinkedHashMap::new() }
+    pub fn with_identifier<S: Into<String>>(name: S) -> SchemaBuilder {
+        SchemaBuilder {
+            identifier: name.into(),
+            attrs: LinkedHashMap::new(),
+        }
     }
 
     pub fn new_attribute<S: Into<String>>(&mut self, name: S, props: SchemaProps) -> SchemaAttr {
@@ -65,7 +74,8 @@ impl SchemaBuilder {
             props.push((name, prop));
         }
 
-        Schema { inner: Arc::new(InnerSchema { attrs, props }) }
+        let identifier = self.identifier;
+        Schema { inner: Arc::new(InnerSchema { identifier, attrs, props }) }
     }
 }
 
@@ -76,6 +86,7 @@ pub struct Schema {
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 struct InnerSchema {
+    identifier: String,
     attrs: HashMap<String, SchemaAttr>,
     props: Vec<(String, SchemaProps)>,
 }
@@ -87,8 +98,8 @@ impl Schema {
     }
 
     pub fn read_from<R: Read>(reader: R) -> bincode::Result<Schema> {
-        let attrs = bincode::deserialize_from(reader)?;
-        let builder = SchemaBuilder { attrs };
+        let (identifier, attrs) = bincode::deserialize_from(reader)?;
+        let builder = SchemaBuilder { identifier, attrs };
         Ok(builder.build())
     }
 
@@ -99,12 +110,22 @@ impl Schema {
             ordered.insert(attr.0, (name, props));
         }
 
+        let identifier = &self.inner.identifier;
         let mut attrs = LinkedHashMap::with_capacity(ordered.len());
         for (_, (name, props)) in ordered {
             attrs.insert(name, props);
         }
 
-        bincode::serialize_into(writer, &attrs)
+        bincode::serialize_into(writer, &(identifier, attrs))
+    }
+
+    pub fn document_id<T>(&self, document: &T) -> Result<DocumentId, SerializerError>
+    where T: Serialize,
+    {
+        let find_document_id = FindDocumentIdSerializer {
+            id_attribute_name: self.identifier_name(),
+        };
+        document.serialize(find_document_id)
     }
 
     pub fn props(&self, attr: SchemaAttr) -> SchemaProps {
@@ -112,6 +133,10 @@ impl Schema {
         props
     }
 
+    pub fn identifier_name(&self) -> &str {
+        &self.inner.identifier
+    }
+
     pub fn attribute<S: AsRef<str>>(&self, name: S) -> Option<SchemaAttr> {
         self.inner.attrs.get(name.as_ref()).cloned()
     }
@@ -141,13 +166,199 @@ impl fmt::Display for SchemaAttr {
     }
 }
 
+struct FindDocumentIdSerializer<'a> {
+    id_attribute_name: &'a str,
+}
+
+impl<'a> ser::Serializer for FindDocumentIdSerializer<'a> {
+    type Ok = DocumentId;
+    type Error = SerializerError;
+    type SerializeSeq = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeTuple = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeTupleStruct = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeTupleVariant = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeMap = ser::Impossible<Self::Ok, Self::Error>;
+    type SerializeStruct = FindDocumentIdStructSerializer<'a>;
+    type SerializeStructVariant = ser::Impossible<Self::Ok, Self::Error>;
+
+    forward_to_unserializable_type! {
+        bool => serialize_bool,
+        char => serialize_char,
+
+        i8  => serialize_i8,
+        i16 => serialize_i16,
+        i32 => serialize_i32,
+        i64 => serialize_i64,
+
+        u8  => serialize_u8,
+        u16 => serialize_u16,
+        u32 => serialize_u32,
+        u64 => serialize_u64,
+
+        f32 => serialize_f32,
+        f64 => serialize_f64,
+    }
+
+    fn serialize_str(self, _v: &str) -> Result<Self::Ok, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "str" })
+    }
+
+    fn serialize_bytes(self, _v: &[u8]) -> Result<Self::Ok, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "&[u8]" })
+    }
+
+    fn serialize_none(self) -> Result<Self::Ok, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "Option" })
+    }
+
+    fn serialize_some<T: ?Sized>(self, _value: &T) -> Result<Self::Ok, Self::Error>
+    where T: Serialize,
+    {
+        Err(SerializerError::UnserializableType { name: "Option" })
+    }
+
+    fn serialize_unit(self) -> Result<Self::Ok, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "()" })
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Self::Ok, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "unit struct" })
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str
+    ) -> Result<Self::Ok, Self::Error>
+    {
+        Err(SerializerError::UnserializableType { name: "unit variant" })
+    }
+
+    fn serialize_newtype_struct<T: ?Sized>(
+        self,
+        _name: &'static str,
+        value: &T
+    ) -> Result<Self::Ok, Self::Error>
+    where T: Serialize,
+    {
+        value.serialize(self)
+    }
+
+    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(SerializerError::UnserializableType { name: "newtype variant" })
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "sequence" })
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple, Self::Error> {
+        Err(SerializerError::UnserializableType { name: "tuple" })
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize
+    ) -> Result<Self::SerializeTupleStruct, Self::Error>
+    {
+        Err(SerializerError::UnserializableType { name: "tuple struct" })
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize
+    ) -> Result<Self::SerializeTupleVariant, Self::Error>
+    {
+        Err(SerializerError::UnserializableType { name: "tuple variant" })
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap, Self::Error> {
+        // Ok(MapSerializer {
+        //     schema: self.schema,
+        //     document_id: self.document_id,
+        //     new_states: self.new_states,
+        // })
+        Err(SerializerError::UnserializableType { name: "map" })
+    }
+
+    fn serialize_struct(
+        self,
+        _name: &'static str,
+        _len: usize
+    ) -> Result<Self::SerializeStruct, Self::Error>
+    {
+        Ok(FindDocumentIdStructSerializer {
+            id_attribute_name: self.id_attribute_name,
+            document_id: None,
+        })
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize
+    ) -> Result<Self::SerializeStructVariant, Self::Error>
+    {
+        Err(SerializerError::UnserializableType { name: "struct variant" })
+    }
+}
+
+struct FindDocumentIdStructSerializer<'a> {
+    id_attribute_name: &'a str,
+    document_id: Option<DocumentId>,
+}
+
+impl<'a> ser::SerializeStruct for FindDocumentIdStructSerializer<'a> {
+    type Ok = DocumentId;
+    type Error = SerializerError;
+
+    fn serialize_field<T: ?Sized>(
+        &mut self,
+        key: &'static str,
+        value: &T
+    ) -> Result<(), Self::Error>
+    where T: Serialize,
+    {
+        if self.id_attribute_name == key {
+            // TODO can it be possible to have multiple ids?
+            let id = bincode::serialize(value).unwrap();
+            let hash = calculate_hash(&id);
+            self.document_id = Some(DocumentId(hash));
+        }
+
+        Ok(())
+    }
+
+    fn end(self) -> Result<Self::Ok, Self::Error> {
+        match self.document_id {
+            Some(document_id) => Ok(document_id),
+            None => Err(SerializerError::DocumentIdNotFound)
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
 
     #[test]
     fn serialize_deserialize() -> bincode::Result<()> {
-        let mut builder = SchemaBuilder::new();
+        let mut builder = SchemaBuilder::with_identifier("id");
         builder.new_attribute("alphabet", STORED);
         builder.new_attribute("beta", STORED | INDEXED);
         builder.new_attribute("gamma", INDEXED);
diff --git a/src/database/update/mod.rs b/src/database/update/mod.rs
index d298a656f..433624022 100644
--- a/src/database/update/mod.rs
+++ b/src/database/update/mod.rs
@@ -4,7 +4,7 @@ use std::error::Error;
 mod negative;
 mod positive;
 
-pub use self::positive::{PositiveUpdateBuilder, NewState};
+pub use self::positive::{PositiveUpdateBuilder, NewState, SerializerError};
 pub use self::negative::NegativeUpdateBuilder;
 
 pub struct Update {
diff --git a/src/database/update/positive/mod.rs b/src/database/update/positive/mod.rs
index e05bd9dff..414f88722 100644
--- a/src/database/update/positive/mod.rs
+++ b/src/database/update/positive/mod.rs
@@ -1,4 +1,4 @@
 mod update;
 mod unordered_builder;
 
-pub use self::update::{PositiveUpdateBuilder, NewState};
+pub use self::update::{PositiveUpdateBuilder, NewState, SerializerError};
diff --git a/src/database/update/positive/update.rs b/src/database/update/positive/update.rs
index 595307cd2..de064e5a1 100644
--- a/src/database/update/positive/update.rs
+++ b/src/database/update/positive/update.rs
@@ -40,18 +40,21 @@ impl<B> PositiveUpdateBuilder<B> {
         }
     }
 
-    pub fn update<T: Serialize>(&mut self, id: DocumentId, document: &T) -> Result<(), Box<Error>>
+    pub fn update<T: Serialize>(&mut self, document: &T) -> Result<DocumentId, SerializerError>
     where B: TokenizerBuilder
     {
+        let document_id = self.schema.document_id(document)?;
+
         let serializer = Serializer {
             schema: &self.schema,
-            document_id: id,
             tokenizer_builder: &self.tokenizer_builder,
+            document_id: document_id,
             builder: &mut self.builder,
             new_states: &mut self.new_states
         };
+        document.serialize(serializer)?;
 
-        Ok(ser::Serialize::serialize(document, serializer)?)
+        Ok(document_id)
     }
 
     // TODO value must be a field that can be indexed
@@ -67,7 +70,7 @@ impl<B> PositiveUpdateBuilder<B> {
 
 #[derive(Debug)]
 pub enum SerializerError {
-    SchemaDontMatch { attribute: String },
+    DocumentIdNotFound,
     UnserializableType { name: &'static str },
     Custom(String),
 }
@@ -81,10 +84,9 @@ impl ser::Error for SerializerError {
 impl fmt::Display for SerializerError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self {
-            SerializerError::SchemaDontMatch { attribute } => {
-                write!(f, "serialized document try to specify the \
-                           {:?} attribute that is not known by the schema", attribute)
-            },
+            SerializerError::DocumentIdNotFound => {
+                write!(f, "serialized document does not have an id according to the schema")
+            }
             SerializerError::UnserializableType { name } => {
                 write!(f, "Only struct and map types are considered valid documents and
                            can be serialized, not {} types directly.", name)
@@ -104,16 +106,6 @@ struct Serializer<'a, B> {
     new_states: &'a mut BTreeMap<DocumentKeyAttr, NewState>,
 }
 
-macro_rules! forward_to_unserializable_type {
-    ($($ty:ident => $se_method:ident,)*) => {
-        $(
-            fn $se_method(self, _v: $ty) -> Result<Self::Ok, Self::Error> {
-                Err(SerializerError::UnserializableType { name: "$ty" })
-            }
-        )*
-    }
-}
-
 impl<'a, B> ser::Serializer for Serializer<'a, B>
 where B: TokenizerBuilder
 {
@@ -288,27 +280,25 @@ where B: TokenizerBuilder
     ) -> Result<(), Self::Error>
     where T: Serialize,
     {
-        match self.schema.attribute(key) {
-            Some(attr) => {
-                let props = self.schema.props(attr);
-                if props.is_stored() {
-                    let value = bincode::serialize(value).unwrap();
-                    let key = DocumentKeyAttr::new(self.document_id, attr);
-                    self.new_states.insert(key, NewState::Updated { value });
-                }
-                if props.is_indexed() {
-                    let serializer = IndexerSerializer {
-                        builder: self.builder,
-                        tokenizer_builder: self.tokenizer_builder,
-                        document_id: self.document_id,
-                        attribute: attr,
-                    };
-                    value.serialize(serializer)?;
-                }
-                Ok(())
-            },
-            None => Err(SerializerError::SchemaDontMatch { attribute: key.to_owned() }),
+        if let Some(attr) = self.schema.attribute(key) {
+            let props = self.schema.props(attr);
+            if props.is_stored() {
+                let value = bincode::serialize(value).unwrap();
+                let key = DocumentKeyAttr::new(self.document_id, attr);
+                self.new_states.insert(key, NewState::Updated { value });
+            }
+            if props.is_indexed() {
+                let serializer = IndexerSerializer {
+                    builder: self.builder,
+                    tokenizer_builder: self.tokenizer_builder,
+                    document_id: self.document_id,
+                    attribute: attr,
+                };
+                value.serialize(serializer)?;
+            }
         }
+
+        Ok(())
     }
 
     fn end(self) -> Result<Self::Ok, Self::Error> {
diff --git a/src/lib.rs b/src/lib.rs
index 10daf8d4f..2bb82a4b3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -18,7 +18,7 @@ pub use self::common_words::CommonWords;
 /// It is used to inform the database the document you want to deserialize.
 /// Helpful for custom ranking.
 #[derive(Debug, Copy, Clone, Eq, PartialEq, PartialOrd, Ord, Hash)]
-pub struct DocumentId(pub u64);
+pub struct DocumentId(u64);
 
 /// Represent an attribute number along with the word index
 /// according to the tokenizer used.
diff --git a/src/rank/criterion/sort_by.rs b/src/rank/criterion/sort_by.rs
index 7f60962aa..bce8d0d90 100644
--- a/src/rank/criterion/sort_by.rs
+++ b/src/rank/criterion/sort_by.rs
@@ -62,12 +62,12 @@ where D: Deref<Target=DB>,
       T: DeserializeOwned + Ord,
 {
     fn evaluate(&self, lhs: &Document, rhs: &Document, view: &DatabaseView<D>) -> Ordering {
-        let lhs = match view.retrieve_document::<T>(lhs.id) {
+        let lhs = match view.document_by_id::<T>(lhs.id) {
             Ok(doc) => Some(doc),
             Err(e) => { eprintln!("{}", e); None },
         };
 
-        let rhs = match view.retrieve_document::<T>(rhs.id) {
+        let rhs = match view.document_by_id::<T>(rhs.id) {
             Ok(doc) => Some(doc),
             Err(e) => { eprintln!("{}", e); None },
         };