Merge branch 'indexer-edition-2024' into indexer-edition-2024-doc-chunks

crates/milli/src/documents/builder.rs

@@ -0,0 +1,600 @@
+use std::io::{self, Write};
+
+use grenad::{CompressionType, WriterBuilder};
+use serde::de::Deserializer;
+use serde_json::{to_writer, Value};
+
+use super::{DocumentsBatchIndex, Error, DOCUMENTS_BATCH_INDEX_KEY};
+use crate::documents::serde_impl::DocumentVisitor;
+use crate::Object;
+
+/// The `DocumentsBatchBuilder` provides a way to build a documents batch in the intermediary
+/// format used by milli.
+///
+/// The writer used by the `DocumentsBatchBuilder` can be read using a `DocumentsBatchReader`
+/// to iterate over the documents.
+///
+/// ## example:
+/// ```
+/// use serde_json::json;
+/// use milli::documents::DocumentsBatchBuilder;
+///
+/// let json = json!({ "id": 1, "name": "foo" });
+///
+/// let mut builder = DocumentsBatchBuilder::new(Vec::new());
+/// builder.append_json_object(json.as_object().unwrap()).unwrap();
+/// let _vector = builder.into_inner().unwrap();
+/// ```
+pub struct DocumentsBatchBuilder<W> {
+    /// The inner grenad writer, the last value must always be the `DocumentsBatchIndex`.
+    writer: grenad::Writer<W>,
+    /// A map that creates the relation between field ids and field names.
+    fields_index: DocumentsBatchIndex,
+    /// The number of documents that were added to this builder,
+    /// it doesn't take the primary key of the documents into account at this point.
+    documents_count: u32,
+
+    /// A buffer to store a temporary obkv buffer and avoid reallocating.
+    obkv_buffer: Vec<u8>,
+    /// A buffer to serialize the values and avoid reallocating,
+    /// serialized values are stored in an obkv.
+    value_buffer: Vec<u8>,
+}
+
+impl<W: Write> DocumentsBatchBuilder<W> {
+    pub fn new(writer: W) -> DocumentsBatchBuilder<W> {
+        DocumentsBatchBuilder {
+            writer: WriterBuilder::new().compression_type(CompressionType::None).build(writer),
+            fields_index: DocumentsBatchIndex::default(),
+            documents_count: 0,
+            obkv_buffer: Vec::new(),
+            value_buffer: Vec::new(),
+        }
+    }
+
+    /// Returns the number of documents inserted into this builder.
+    pub fn documents_count(&self) -> u32 {
+        self.documents_count
+    }
+
+    /// Appends a new JSON object into the batch and updates the `DocumentsBatchIndex` accordingly.
+    pub fn append_json_object(&mut self, object: &Object) -> io::Result<()> {
+        // Make sure that we insert the fields ids in order as the obkv writer has this requirement.
+        let mut fields_ids: Vec<_> = object.keys().map(|k| self.fields_index.insert(k)).collect();
+        fields_ids.sort_unstable();
+
+        self.obkv_buffer.clear();
+        let mut writer = obkv::KvWriter::new(&mut self.obkv_buffer);
+        for field_id in fields_ids {
+            let key = self.fields_index.name(field_id).unwrap();
+            self.value_buffer.clear();
+            to_writer(&mut self.value_buffer, &object[key])?;
+            writer.insert(field_id, &self.value_buffer)?;
+        }
+
+        let internal_id = self.documents_count.to_be_bytes();
+        let document_bytes = writer.into_inner()?;
+        self.writer.insert(internal_id, &document_bytes)?;
+        self.documents_count += 1;
+
+        Ok(())
+    }
+
+    /// Appends a new JSON array of objects into the batch and updates the `DocumentsBatchIndex` accordingly.
+    pub fn append_json_array<R: io::Read>(&mut self, reader: R) -> Result<(), Error> {
+        let mut de = serde_json::Deserializer::from_reader(reader);
+        let mut visitor = DocumentVisitor::new(self);
+        de.deserialize_any(&mut visitor)?
+    }
+
+    /// Appends a new CSV file into the batch and updates the `DocumentsBatchIndex` accordingly.
+    pub fn append_csv<R: io::Read>(&mut self, mut reader: csv::Reader<R>) -> Result<(), Error> {
+        // Make sure that we insert the fields ids in order as the obkv writer has this requirement.
+        let mut typed_fields_ids: Vec<_> = reader
+            .headers()?
+            .into_iter()
+            .map(parse_csv_header)
+            .map(|(k, t)| (self.fields_index.insert(k), t))
+            .enumerate()
+            .collect();
+        // Make sure that we insert the fields ids in order as the obkv writer has this requirement.
+        typed_fields_ids.sort_unstable_by_key(|(_, (fid, _))| *fid);
+
+        let mut record = csv::StringRecord::new();
+        let mut line = 0;
+        while reader.read_record(&mut record)? {
+            // We increment here and not at the end of the while loop to take
+            // the header offset into account.
+            line += 1;
+
+            self.obkv_buffer.clear();
+            let mut writer = obkv::KvWriter::new(&mut self.obkv_buffer);
+
+            for (i, (field_id, type_)) in typed_fields_ids.iter() {
+                self.value_buffer.clear();
+
+                let value = &record[*i];
+                let trimmed_value = value.trim();
+                match type_ {
+                    AllowedType::Number => {
+                        if trimmed_value.is_empty() {
+                            to_writer(&mut self.value_buffer, &Value::Null)?;
+                        } else if let Ok(integer) = trimmed_value.parse::<i64>() {
+                            to_writer(&mut self.value_buffer, &integer)?;
+                        } else {
+                            match trimmed_value.parse::<f64>() {
+                                Ok(float) => {
+                                    to_writer(&mut self.value_buffer, &float)?;
+                                }
+                                Err(error) => {
+                                    return Err(Error::ParseFloat {
+                                        error,
+                                        line,
+                                        value: value.to_string(),
+                                    });
+                                }
+                            }
+                        }
+                    }
+                    AllowedType::Boolean => {
+                        if trimmed_value.is_empty() {
+                            to_writer(&mut self.value_buffer, &Value::Null)?;
+                        } else {
+                            match trimmed_value.parse::<bool>() {
+                                Ok(bool) => {
+                                    to_writer(&mut self.value_buffer, &bool)?;
+                                }
+                                Err(error) => {
+                                    return Err(Error::ParseBool {
+                                        error,
+                                        line,
+                                        value: value.to_string(),
+                                    });
+                                }
+                            }
+                        }
+                    }
+                    AllowedType::String => {
+                        if value.is_empty() {
+                            to_writer(&mut self.value_buffer, &Value::Null)?;
+                        } else {
+                            to_writer(&mut self.value_buffer, value)?;
+                        }
+                    }
+                }
+
+                // We insert into the obkv writer the value buffer that has been filled just above.
+                writer.insert(*field_id, &self.value_buffer)?;
+            }
+
+            let internal_id = self.documents_count.to_be_bytes();
+            let document_bytes = writer.into_inner()?;
+            self.writer.insert(internal_id, &document_bytes)?;
+            self.documents_count += 1;
+        }
+
+        Ok(())
+    }
+
+    /// Flushes the content on disk and stores the final version of the `DocumentsBatchIndex`.
+    pub fn into_inner(mut self) -> io::Result<W> {
+        let DocumentsBatchBuilder { mut writer, fields_index, .. } = self;
+
+        // We serialize and insert the `DocumentsBatchIndex` as the last key of the grenad writer.
+        self.value_buffer.clear();
+        to_writer(&mut self.value_buffer, &fields_index)?;
+        writer.insert(DOCUMENTS_BATCH_INDEX_KEY, &self.value_buffer)?;
+
+        writer.into_inner()
+    }
+}
+
+#[derive(Debug)]
+enum AllowedType {
+    String,
+    Boolean,
+    Number,
+}
+
+fn parse_csv_header(header: &str) -> (&str, AllowedType) {
+    // if there are several separators we only split on the last one.
+    match header.rsplit_once(':') {
+        Some((field_name, field_type)) => match field_type {
+            "string" => (field_name, AllowedType::String),
+            "boolean" => (field_name, AllowedType::Boolean),
+            "number" => (field_name, AllowedType::Number),
+            // if the pattern isn't recognized, we keep the whole field.
+            _otherwise => (header, AllowedType::String),
+        },
+        None => (header, AllowedType::String),
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::io::Cursor;
+
+    use serde_json::json;
+
+    use super::*;
+    use crate::documents::{obkv_to_object, DocumentsBatchReader};
+
+    #[test]
+    fn add_single_documents_json() {
+        let json = serde_json::json!({
+            "id": 1,
+            "field": "hello!",
+        });
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_json_object(json.as_object().unwrap()).unwrap();
+
+        let json = serde_json::json!({
+            "blabla": false,
+            "field": "hello!",
+            "id": 1,
+        });
+
+        builder.append_json_object(json.as_object().unwrap()).unwrap();
+
+        assert_eq!(builder.documents_count(), 2);
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+        assert_eq!(index.len(), 3);
+
+        let document = cursor.next_document().unwrap().unwrap();
+        assert_eq!(document.iter().count(), 2);
+
+        let document = cursor.next_document().unwrap().unwrap();
+        assert_eq!(document.iter().count(), 3);
+
+        assert!(cursor.next_document().unwrap().is_none());
+    }
+
+    #[test]
+    fn add_documents_csv() {
+        let csv_content = "id:number,field:string\n1,hello!\n2,blabla";
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        assert_eq!(builder.documents_count(), 2);
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+        assert_eq!(index.len(), 2);
+
+        let document = cursor.next_document().unwrap().unwrap();
+        assert_eq!(document.iter().count(), 2);
+
+        let document = cursor.next_document().unwrap().unwrap();
+        assert_eq!(document.iter().count(), 2);
+
+        assert!(cursor.next_document().unwrap().is_none());
+    }
+
+    #[test]
+    fn simple_csv_document() {
+        let csv_content = r#"city,country,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city": "Boston",
+                "country": "United States",
+                "pop": "4628910",
+            })
+        );
+
+        assert!(cursor.next_document().unwrap().is_none());
+    }
+
+    #[test]
+    fn coma_in_field() {
+        let csv_content = r#"city,country,pop
+"Boston","United, States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city": "Boston",
+                "country": "United, States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[test]
+    fn quote_in_field() {
+        let csv_content = r#"city,country,pop
+"Boston","United"" States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city": "Boston",
+                "country": "United\" States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[test]
+    fn integer_in_field() {
+        let csv_content = r#"city,country,pop:number
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city": "Boston",
+                "country": "United States",
+                "pop": 4628910,
+            })
+        );
+    }
+
+    #[test]
+    fn integer_as_id() {
+        let csv_content = r#""id:number","title:string","comment:string"
+"1239","Pride and Prejudice","A great book""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "id": 1239,
+                "title": "Pride and Prejudice",
+                "comment": "A great book",
+            })
+        );
+    }
+
+    #[test]
+    fn float_in_field() {
+        let csv_content = r#"city,country,pop:number
+"Boston","United States","4628910.01""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city": "Boston",
+                "country": "United States",
+                "pop": 4628910.01,
+            })
+        );
+    }
+
+    #[test]
+    fn several_colon_in_header() {
+        let csv_content = r#"city:love:string,country:state,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city:love": "Boston",
+                "country:state": "United States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[test]
+    fn ending_by_colon_in_header() {
+        let csv_content = r#"city:,country,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city:": "Boston",
+                "country": "United States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[test]
+    fn starting_by_colon_in_header() {
+        let csv_content = r#":city,country,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                ":city": "Boston",
+                "country": "United States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[ignore]
+    #[test]
+    fn starting_by_colon_in_header2() {
+        let csv_content = r#":string,country,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, _) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        assert!(cursor.next_document().is_err());
+    }
+
+    #[test]
+    fn double_colon_in_header() {
+        let csv_content = r#"city::string,country,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut cursor, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        let doc = cursor.next_document().unwrap().unwrap();
+        let val = obkv_to_object(doc, &index).map(Value::from).unwrap();
+
+        assert_eq!(
+            val,
+            json!({
+                "city:": "Boston",
+                "country": "United States",
+                "pop": "4628910",
+            })
+        );
+    }
+
+    #[test]
+    fn bad_type_in_header() {
+        let csv_content = r#"city,country:number,pop
+"Boston","United States","4628910""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        assert!(builder.append_csv(csv).is_err());
+    }
+
+    #[test]
+    fn bad_column_count1() {
+        let csv_content = r#"city,country,pop
+"Boston","United States","4628910", "too much
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content"#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        assert!(builder.append_csv(csv).is_err());
+    }
+
+    #[test]
+    fn bad_column_count2() {
+        let csv_content = r#"city,country,pop
+"Boston","United States""#;
+        let csv = csv::Reader::from_reader(Cursor::new(csv_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        assert!(builder.append_csv(csv).is_err());
+    }
+}

crates/milli/src/documents/enriched.rs

@@ -0,0 +1,110 @@
+use std::fs::File;
+use std::io::BufReader;
+use std::{io, str};
+
+use obkv::KvReader;
+
+use super::{
+    DocumentsBatchCursor, DocumentsBatchCursorError, DocumentsBatchIndex, DocumentsBatchReader,
+    Error,
+};
+use crate::update::DocumentId;
+use crate::FieldId;
+
+/// The `EnrichedDocumentsBatchReader` provides a way to iterate over documents that have
+/// been created with a `DocumentsBatchWriter` and, for the enriched data,
+/// a simple `grenad::Reader<File>`.
+///
+/// The documents are returned in the form of `obkv::Reader` where each field is identified with a
+/// `FieldId`. The mapping between the field ids and the field names is done thanks to the index.
+pub struct EnrichedDocumentsBatchReader<R> {
+    documents: DocumentsBatchReader<R>,
+    primary_key: String,
+    external_ids: grenad::ReaderCursor<BufReader<File>>,
+}
+
+impl<R: io::Read + io::Seek> EnrichedDocumentsBatchReader<R> {
+    pub fn new(
+        documents: DocumentsBatchReader<R>,
+        primary_key: String,
+        external_ids: grenad::Reader<BufReader<File>>,
+    ) -> Result<Self, Error> {
+        if documents.documents_count() as u64 == external_ids.len() {
+            Ok(EnrichedDocumentsBatchReader {
+                documents,
+                primary_key,
+                external_ids: external_ids.into_cursor()?,
+            })
+        } else {
+            Err(Error::InvalidEnrichedData)
+        }
+    }
+
+    pub fn documents_count(&self) -> u32 {
+        self.documents.documents_count()
+    }
+
+    pub fn primary_key(&self) -> &str {
+        &self.primary_key
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.documents.is_empty()
+    }
+
+    pub fn documents_batch_index(&self) -> &DocumentsBatchIndex {
+        self.documents.documents_batch_index()
+    }
+
+    /// This method returns a forward cursor over the enriched documents.
+    pub fn into_cursor_and_fields_index(
+        self,
+    ) -> (EnrichedDocumentsBatchCursor<R>, DocumentsBatchIndex) {
+        let EnrichedDocumentsBatchReader { documents, primary_key, mut external_ids } = self;
+        let (documents, fields_index) = documents.into_cursor_and_fields_index();
+        external_ids.reset();
+        (EnrichedDocumentsBatchCursor { documents, primary_key, external_ids }, fields_index)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct EnrichedDocument<'a> {
+    pub document: &'a KvReader<FieldId>,
+    pub document_id: DocumentId,
+}
+
+pub struct EnrichedDocumentsBatchCursor<R> {
+    documents: DocumentsBatchCursor<R>,
+    primary_key: String,
+    external_ids: grenad::ReaderCursor<BufReader<File>>,
+}
+
+impl<R> EnrichedDocumentsBatchCursor<R> {
+    pub fn primary_key(&self) -> &str {
+        &self.primary_key
+    }
+    /// Resets the cursor to be able to read from the start again.
+    pub fn reset(&mut self) {
+        self.documents.reset();
+        self.external_ids.reset();
+    }
+}
+
+impl<R: io::Read + io::Seek> EnrichedDocumentsBatchCursor<R> {
+    /// Returns the next document, starting from the first one. Subsequent calls to
+    /// `next_document` advance the document reader until all the documents have been read.
+    pub fn next_enriched_document(
+        &mut self,
+    ) -> Result<Option<EnrichedDocument<'_>>, DocumentsBatchCursorError> {
+        let document = self.documents.next_document()?;
+        let document_id = match self.external_ids.move_on_next()? {
+            Some((_, bytes)) => serde_json::from_slice(bytes).map(Some)?,
+            None => None,
+        };
+
+        match document.zip(document_id) {
+            Some((document, document_id)) => Ok(Some(EnrichedDocument { document, document_id })),
+            None => Ok(None),
+        }
+    }
+}

crates/milli/src/documents/mod.rs

@@ -0,0 +1,277 @@
+mod builder;
+mod enriched;
+mod primary_key;
+mod reader;
+mod serde_impl;
+
+use std::fmt::Debug;
+use std::io;
+use std::str::Utf8Error;
+
+use bimap::BiHashMap;
+pub use builder::DocumentsBatchBuilder;
+pub use enriched::{EnrichedDocument, EnrichedDocumentsBatchCursor, EnrichedDocumentsBatchReader};
+use obkv::KvReader;
+pub use primary_key::{
+    validate_document_id_str, validate_document_id_value, DocumentIdExtractionError, FieldIdMapper,
+    PrimaryKey, DEFAULT_PRIMARY_KEY,
+};
+pub use reader::{DocumentsBatchCursor, DocumentsBatchCursorError, DocumentsBatchReader};
+use serde::{Deserialize, Serialize};
+
+use crate::error::{FieldIdMapMissingEntry, InternalError};
+use crate::{FieldId, Object, Result};
+
+/// The key that is used to store the `DocumentsBatchIndex` datastructure,
+/// it is the absolute last key of the list.
+const DOCUMENTS_BATCH_INDEX_KEY: [u8; 8] = u64::MAX.to_be_bytes();
+
+/// Helper function to convert an obkv reader into a JSON object.
+pub fn obkv_to_object(obkv: &KvReader<FieldId>, index: &DocumentsBatchIndex) -> Result<Object> {
+    obkv.iter()
+        .map(|(field_id, value)| {
+            let field_name = index
+                .name(field_id)
+                .ok_or(FieldIdMapMissingEntry::FieldId { field_id, process: "obkv_to_object" })?;
+            let value = serde_json::from_slice(value).map_err(InternalError::SerdeJson)?;
+            Ok((field_name.to_string(), value))
+        })
+        .collect()
+}
+
+/// A bidirectional map that links field ids to their name in a document batch.
+#[derive(Default, Clone, Debug, Serialize, Deserialize)]
+pub struct DocumentsBatchIndex(pub BiHashMap<FieldId, String>);
+
+impl DocumentsBatchIndex {
+    /// Insert the field in the map, or return it's field id if it doesn't already exists.
+    pub fn insert(&mut self, field: &str) -> FieldId {
+        match self.0.get_by_right(field) {
+            Some(field_id) => *field_id,
+            None => {
+                let field_id = self.0.len() as FieldId;
+                self.0.insert(field_id, field.to_string());
+                field_id
+            }
+        }
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
+    pub fn len(&self) -> usize {
+        self.0.len()
+    }
+
+    pub fn iter(&self) -> bimap::hash::Iter<'_, FieldId, String> {
+        self.0.iter()
+    }
+
+    pub fn name(&self, id: FieldId) -> Option<&str> {
+        self.0.get_by_left(&id).map(AsRef::as_ref)
+    }
+
+    pub fn id(&self, name: &str) -> Option<FieldId> {
+        self.0.get_by_right(name).cloned()
+    }
+
+    pub fn recreate_json(&self, document: &obkv::KvReaderU16) -> Result<Object> {
+        let mut map = Object::new();
+
+        for (k, v) in document.iter() {
+            // TODO: TAMO: update the error type
+            let key =
+                self.0.get_by_left(&k).ok_or(crate::error::InternalError::DatabaseClosing)?.clone();
+            let value = serde_json::from_slice::<serde_json::Value>(v)
+                .map_err(crate::error::InternalError::SerdeJson)?;
+            map.insert(key, value);
+        }
+
+        Ok(map)
+    }
+}
+
+impl FieldIdMapper for DocumentsBatchIndex {
+    fn id(&self, name: &str) -> Option<FieldId> {
+        self.id(name)
+    }
+
+    fn name(&self, id: FieldId) -> Option<&str> {
+        self.name(id)
+    }
+}
+
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    #[error("Error parsing number {value:?} at line {line}: {error}")]
+    ParseFloat { error: std::num::ParseFloatError, line: usize, value: String },
+    #[error("Error parsing boolean {value:?} at line {line}: {error}")]
+    ParseBool { error: std::str::ParseBoolError, line: usize, value: String },
+    #[error("Invalid document addition format, missing the documents batch index.")]
+    InvalidDocumentFormat,
+    #[error("Invalid enriched data.")]
+    InvalidEnrichedData,
+    #[error(transparent)]
+    InvalidUtf8(#[from] Utf8Error),
+    #[error(transparent)]
+    Csv(#[from] csv::Error),
+    #[error(transparent)]
+    Json(#[from] serde_json::Error),
+    #[error(transparent)]
+    Serialize(serde_json::Error),
+    #[error(transparent)]
+    Grenad(#[from] grenad::Error),
+    #[error(transparent)]
+    Io(#[from] io::Error),
+}
+
+pub fn objects_from_json_value(json: serde_json::Value) -> Vec<crate::Object> {
+    let documents = match json {
+        object @ serde_json::Value::Object(_) => vec![object],
+        serde_json::Value::Array(objects) => objects,
+        invalid => {
+            panic!("an array of objects must be specified, {:#?} is not an array", invalid)
+        }
+    };
+    let mut objects = vec![];
+    for document in documents {
+        let object = match document {
+            serde_json::Value::Object(object) => object,
+            invalid => panic!("an object must be specified, {:#?} is not an object", invalid),
+        };
+        objects.push(object);
+    }
+    objects
+}
+
+/// Macro used to generate documents, with the same syntax as `serde_json::json`
+#[cfg(test)]
+macro_rules! documents {
+    ($data:tt) => {{
+        let documents = serde_json::json!($data);
+        let documents = $crate::documents::objects_from_json_value(documents);
+        $crate::documents::documents_batch_reader_from_objects(documents)
+    }};
+}
+
+pub fn documents_batch_reader_from_objects(
+    objects: impl IntoIterator<Item = Object>,
+) -> DocumentsBatchReader<std::io::Cursor<Vec<u8>>> {
+    let mut builder = DocumentsBatchBuilder::new(Vec::new());
+    for object in objects {
+        builder.append_json_object(&object).unwrap();
+    }
+    let vector = builder.into_inner().unwrap();
+    DocumentsBatchReader::from_reader(std::io::Cursor::new(vector)).unwrap()
+}
+
+#[cfg(test)]
+mod test {
+    use std::io::Cursor;
+
+    use serde_json::{json, Value};
+
+    use super::*;
+
+    #[test]
+    fn create_documents_no_errors() {
+        let value = json!({
+            "number": 1,
+            "string": "this is a field",
+            "array": ["an", "array"],
+            "object": {
+                "key": "value",
+            },
+            "bool": true
+        });
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_json_object(value.as_object().unwrap()).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut documents, index) = DocumentsBatchReader::from_reader(Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+
+        assert_eq!(index.iter().count(), 5);
+        let reader = documents.next_document().unwrap().unwrap();
+        assert_eq!(reader.iter().count(), 5);
+        assert!(documents.next_document().unwrap().is_none());
+    }
+
+    #[test]
+    fn test_add_multiple_documents() {
+        let doc1 = json!({
+            "bool": true,
+        });
+        let doc2 = json!({
+            "toto": false,
+        });
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_json_object(doc1.as_object().unwrap()).unwrap();
+        builder.append_json_object(doc2.as_object().unwrap()).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        let (mut documents, index) = DocumentsBatchReader::from_reader(io::Cursor::new(vector))
+            .unwrap()
+            .into_cursor_and_fields_index();
+        assert_eq!(index.iter().count(), 2);
+        let reader = documents.next_document().unwrap().unwrap();
+        assert_eq!(reader.iter().count(), 1);
+        assert!(documents.next_document().unwrap().is_some());
+        assert!(documents.next_document().unwrap().is_none());
+    }
+
+    #[test]
+    fn test_nested() {
+        let docs_reader = documents!([{
+            "hello": {
+                "toto": ["hello"]
+            }
+        }]);
+
+        let (mut cursor, _) = docs_reader.into_cursor_and_fields_index();
+        let doc = cursor.next_document().unwrap().unwrap();
+        let nested: Value = serde_json::from_slice(doc.get(0).unwrap()).unwrap();
+        assert_eq!(nested, json!({ "toto": ["hello"] }));
+    }
+
+    #[test]
+    fn out_of_order_json_fields() {
+        let _documents = documents!([
+            {"id": 1,"b": 0},
+            {"id": 2,"a": 0,"b": 0},
+        ]);
+    }
+
+    #[test]
+    fn csv_types_dont_panic() {
+        let csv1_content =
+            "id:number,b:boolean,c,d:number\n1,,,\n2,true,doggo,2\n3,false,the best doggo,-2\n4,,\"Hello, World!\",2.5";
+        let csv1 = csv::Reader::from_reader(Cursor::new(csv1_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv1).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        DocumentsBatchReader::from_reader(Cursor::new(vector)).unwrap();
+    }
+
+    #[test]
+    fn out_of_order_csv_fields() {
+        let csv1_content = "id:number,b\n1,0";
+        let csv1 = csv::Reader::from_reader(Cursor::new(csv1_content));
+
+        let csv2_content = "id:number,a,b\n2,0,0";
+        let csv2 = csv::Reader::from_reader(Cursor::new(csv2_content));
+
+        let mut builder = DocumentsBatchBuilder::new(Vec::new());
+        builder.append_csv(csv1).unwrap();
+        builder.append_csv(csv2).unwrap();
+        let vector = builder.into_inner().unwrap();
+
+        DocumentsBatchReader::from_reader(Cursor::new(vector)).unwrap();
+    }
+}

crates/milli/src/documents/primary_key.rs

@@ -0,0 +1,303 @@
+use std::iter;
+use std::ops::ControlFlow;
+use std::result::Result as StdResult;
+
+use bumpalo::Bump;
+use serde_json::value::RawValue;
+use serde_json::Value;
+
+use crate::fields_ids_map::MutFieldIdMapper;
+use crate::update::new::indexer::de::{match_component, DeOrBumpStr};
+use crate::update::new::KvReaderFieldId;
+use crate::{FieldId, InternalError, Object, Result, UserError};
+
+/// The symbol used to define levels in a nested primary key.
+const PRIMARY_KEY_SPLIT_SYMBOL: char = '.';
+
+/// The default primary that is used when not specified.
+pub const DEFAULT_PRIMARY_KEY: &str = "id";
+
+/// Trait for objects that can map the name of a field to its [`FieldId`].
+pub trait FieldIdMapper {
+    /// Attempts to map the passed name to its [`FieldId`].
+    ///
+    /// `None` if the field with this name was not found.
+    fn id(&self, name: &str) -> Option<FieldId>;
+
+    fn name(&self, id: FieldId) -> Option<&str>;
+}
+
+impl<T> FieldIdMapper for &T
+where
+    T: FieldIdMapper,
+{
+    fn id(&self, name: &str) -> Option<FieldId> {
+        T::id(self, name)
+    }
+
+    fn name(&self, id: FieldId) -> Option<&str> {
+        T::name(self, id)
+    }
+}
+
+/// A type that represent the type of primary key that has been set
+/// for this index, a classic flat one or a nested one.
+#[derive(Debug, Clone, Copy)]
+pub enum PrimaryKey<'a> {
+    Flat { name: &'a str, field_id: FieldId },
+    Nested { name: &'a str },
+}
+
+pub enum DocumentIdExtractionError {
+    InvalidDocumentId(UserError),
+    MissingDocumentId,
+    TooManyDocumentIds(usize),
+}
+
+impl<'a> PrimaryKey<'a> {
+    pub fn new(path: &'a str, fields: &impl FieldIdMapper) -> Option<Self> {
+        Some(if path.contains(PRIMARY_KEY_SPLIT_SYMBOL) {
+            Self::Nested { name: path }
+        } else {
+            let field_id = fields.id(path)?;
+            Self::Flat { name: path, field_id }
+        })
+    }
+
+    pub fn new_or_insert(
+        path: &'a str,
+        fields: &mut impl MutFieldIdMapper,
+    ) -> StdResult<Self, UserError> {
+        Ok(if path.contains(PRIMARY_KEY_SPLIT_SYMBOL) {
+            Self::Nested { name: path }
+        } else {
+            let field_id = fields.insert(path).ok_or(UserError::AttributeLimitReached)?;
+            Self::Flat { name: path, field_id }
+        })
+    }
+
+    pub fn name(&self) -> &'a str {
+        match self {
+            PrimaryKey::Flat { name, .. } => name,
+            PrimaryKey::Nested { name } => name,
+        }
+    }
+
+    pub fn document_id(
+        &self,
+        document: &obkv::KvReader<FieldId>,
+        fields: &impl FieldIdMapper,
+    ) -> Result<StdResult<String, DocumentIdExtractionError>> {
+        match self {
+            PrimaryKey::Flat { name: _, field_id } => match document.get(*field_id) {
+                Some(document_id_bytes) => {
+                    let document_id = serde_json::from_slice(document_id_bytes)
+                        .map_err(InternalError::SerdeJson)?;
+                    match validate_document_id_value(document_id) {
+                        Ok(document_id) => Ok(Ok(document_id)),
+                        Err(user_error) => {
+                            Ok(Err(DocumentIdExtractionError::InvalidDocumentId(user_error)))
+                        }
+                    }
+                }
+                None => Ok(Err(DocumentIdExtractionError::MissingDocumentId)),
+            },
+            nested @ PrimaryKey::Nested { .. } => {
+                let mut matching_documents_ids = Vec::new();
+                for (first_level_name, right) in nested.possible_level_names() {
+                    if let Some(field_id) = fields.id(first_level_name) {
+                        if let Some(value_bytes) = document.get(field_id) {
+                            let object = serde_json::from_slice(value_bytes)
+                                .map_err(InternalError::SerdeJson)?;
+                            fetch_matching_values(object, right, &mut matching_documents_ids);
+
+                            if matching_documents_ids.len() >= 2 {
+                                return Ok(Err(DocumentIdExtractionError::TooManyDocumentIds(
+                                    matching_documents_ids.len(),
+                                )));
+                            }
+                        }
+                    }
+                }
+
+                match matching_documents_ids.pop() {
+                    Some(document_id) => match validate_document_id_value(document_id) {
+                        Ok(document_id) => Ok(Ok(document_id)),
+                        Err(user_error) => {
+                            Ok(Err(DocumentIdExtractionError::InvalidDocumentId(user_error)))
+                        }
+                    },
+                    None => Ok(Err(DocumentIdExtractionError::MissingDocumentId)),
+                }
+            }
+        }
+    }
+
+    pub fn extract_docid_from_db<'pl, 'bump: 'pl, Mapper: FieldIdMapper>(
+        &self,
+        document: &'pl KvReaderFieldId,
+        db_fields_ids_map: &Mapper,
+        indexer: &'bump Bump,
+    ) -> Result<DeOrBumpStr<'pl, 'bump>> {
+        use serde::Deserializer as _;
+
+        match self {
+            PrimaryKey::Flat { name: _, field_id } => {
+                let Some(document_id) = document.get(*field_id) else {
+                    return Err(InternalError::DocumentsError(
+                        crate::documents::Error::InvalidDocumentFormat,
+                    )
+                    .into());
+                };
+
+                let document_id: &RawValue =
+                    serde_json::from_slice(document_id).map_err(InternalError::SerdeJson)?;
+
+                let document_id = document_id
+                    .deserialize_any(crate::update::new::indexer::de::DocumentIdVisitor(indexer))
+                    .map_err(InternalError::SerdeJson)?;
+
+                let external_document_id = match document_id {
+                    Ok(document_id) => Ok(document_id),
+                    Err(_) => Err(InternalError::DocumentsError(
+                        crate::documents::Error::InvalidDocumentFormat,
+                    )),
+                }?;
+
+                Ok(external_document_id)
+            }
+            nested @ PrimaryKey::Nested { name: _ } => {
+                let mut docid = None;
+                for (first_level, right) in nested.possible_level_names() {
+                    let Some(fid) = db_fields_ids_map.id(first_level) else { continue };
+
+                    let Some(value) = document.get(fid) else { continue };
+                    let value: &RawValue =
+                        serde_json::from_slice(value).map_err(InternalError::SerdeJson)?;
+                    match match_component(first_level, right, value, indexer, &mut docid) {
+                        ControlFlow::Continue(()) => continue,
+                        ControlFlow::Break(Ok(_)) => {
+                            return Err(InternalError::DocumentsError(
+                                crate::documents::Error::InvalidDocumentFormat,
+                            )
+                            .into())
+                        }
+                        ControlFlow::Break(Err(err)) => {
+                            return Err(InternalError::SerdeJson(err).into())
+                        }
+                    }
+                }
+                Ok(docid.ok_or(InternalError::DocumentsError(
+                    crate::documents::Error::InvalidDocumentFormat,
+                ))?)
+            }
+        }
+    }
+
+    pub fn extract_fields_and_docid<'pl, 'bump: 'pl, Mapper: MutFieldIdMapper>(
+        &self,
+        document: &'pl RawValue,
+        new_fields_ids_map: &mut Mapper,
+        indexer: &'bump Bump,
+    ) -> Result<DeOrBumpStr<'pl, 'bump>> {
+        use serde::Deserializer as _;
+        let res = document
+            .deserialize_map(crate::update::new::indexer::de::FieldAndDocidExtractor::new(
+                new_fields_ids_map,
+                self,
+                indexer,
+            ))
+            .map_err(UserError::SerdeJson)??;
+
+        let external_document_id = match res {
+            Ok(document_id) => Ok(document_id),
+            Err(DocumentIdExtractionError::InvalidDocumentId(e)) => Err(e),
+            Err(DocumentIdExtractionError::MissingDocumentId) => {
+                Err(UserError::MissingDocumentId {
+                    primary_key: self.name().to_string(),
+                    document: serde_json::from_str(document.get()).unwrap(),
+                })
+            }
+            Err(DocumentIdExtractionError::TooManyDocumentIds(_)) => {
+                Err(UserError::TooManyDocumentIds {
+                    primary_key: self.name().to_string(),
+                    document: serde_json::from_str(document.get()).unwrap(),
+                })
+            }
+        }?;
+
+        Ok(external_document_id)
+    }
+
+    /// Returns an `Iterator` that gives all the possible fields names the primary key
+    /// can have depending of the first level name and depth of the objects.
+    pub fn possible_level_names(&self) -> impl Iterator<Item = (&'a str, &'a str)> + '_ {
+        let name = self.name();
+        name.match_indices(PRIMARY_KEY_SPLIT_SYMBOL)
+            .map(move |(i, _)| (&name[..i], &name[i + PRIMARY_KEY_SPLIT_SYMBOL.len_utf8()..]))
+            .chain(iter::once((name, "")))
+    }
+}
+
+fn fetch_matching_values(value: Value, selector: &str, output: &mut Vec<Value>) {
+    match value {
+        Value::Object(object) => fetch_matching_values_in_object(object, selector, "", output),
+        otherwise => output.push(otherwise),
+    }
+}
+
+fn fetch_matching_values_in_object(
+    object: Object,
+    selector: &str,
+    base_key: &str,
+    output: &mut Vec<Value>,
+) {
+    for (key, value) in object {
+        let base_key = if base_key.is_empty() {
+            key.to_string()
+        } else {
+            format!("{}{}{}", base_key, PRIMARY_KEY_SPLIT_SYMBOL, key)
+        };
+
+        if starts_with(selector, &base_key) {
+            match value {
+                Value::Object(object) => {
+                    fetch_matching_values_in_object(object, selector, &base_key, output)
+                }
+                value => output.push(value),
+            }
+        }
+    }
+}
+
+fn starts_with(selector: &str, key: &str) -> bool {
+    selector.strip_prefix(key).map_or(false, |tail| {
+        tail.chars().next().map(|c| c == PRIMARY_KEY_SPLIT_SYMBOL).unwrap_or(true)
+    })
+}
+
+// FIXME: move to a DocumentId struct
+
+pub fn validate_document_id_str(document_id: &str) -> Option<&str> {
+    if document_id.is_empty()
+        || document_id.len() > 512
+        || !document_id.chars().all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_')
+    {
+        None
+    } else {
+        Some(document_id)
+    }
+}
+
+pub fn validate_document_id_value(document_id: Value) -> StdResult<String, UserError> {
+    match document_id {
+        Value::String(string) => match validate_document_id_str(&string) {
+            Some(s) if s.len() == string.len() => Ok(string),
+            Some(s) => Ok(s.to_string()),
+            None => Err(UserError::InvalidDocumentId { document_id: Value::String(string) }),
+        },
+        // a `u64` or `i64` cannot be more than 512 bytes once converted to a string
+        Value::Number(number) if !number.is_f64() => Ok(number.to_string()),
+        content => Err(UserError::InvalidDocumentId { document_id: content }),
+    }
+}

crates/milli/src/documents/reader.rs

@@ -0,0 +1,126 @@
+use std::convert::TryInto;
+use std::{error, fmt, io};
+
+use obkv::KvReader;
+
+use super::{DocumentsBatchIndex, Error, DOCUMENTS_BATCH_INDEX_KEY};
+use crate::FieldId;
+
+/// The `DocumentsBatchReader` provides a way to iterate over documents that have been created with
+/// a `DocumentsBatchWriter`.
+///
+/// The documents are returned in the form of `obkv::Reader` where each field is identified with a
+/// `FieldId`. The mapping between the field ids and the field names is done thanks to the index.
+pub struct DocumentsBatchReader<R> {
+    cursor: grenad::ReaderCursor<R>,
+    fields_index: DocumentsBatchIndex,
+}
+
+impl<R: io::Read + io::Seek> DocumentsBatchReader<R> {
+    pub fn new(cursor: DocumentsBatchCursor<R>, fields_index: DocumentsBatchIndex) -> Self {
+        Self { cursor: cursor.cursor, fields_index }
+    }
+
+    /// Construct a `DocumentsReader` from a reader.
+    ///
+    /// It first retrieves the index, then moves to the first document. Use the `into_cursor`
+    /// method to iterator over the documents, from the first to the last.
+    #[tracing::instrument(level = "trace", skip_all, target = "indexing::documents")]
+    pub fn from_reader(reader: R) -> Result<Self, Error> {
+        let reader = grenad::Reader::new(reader)?;
+        let mut cursor = reader.into_cursor()?;
+
+        let fields_index = match cursor.move_on_key_equal_to(DOCUMENTS_BATCH_INDEX_KEY)? {
+            Some((_, value)) => serde_json::from_slice(value).map_err(Error::Serialize)?,
+            None => return Err(Error::InvalidDocumentFormat),
+        };
+
+        Ok(DocumentsBatchReader { cursor, fields_index })
+    }
+
+    pub fn documents_count(&self) -> u32 {
+        self.cursor.len().saturating_sub(1).try_into().expect("Invalid number of documents")
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.cursor.len().saturating_sub(1) == 0
+    }
+
+    pub fn documents_batch_index(&self) -> &DocumentsBatchIndex {
+        &self.fields_index
+    }
+
+    /// This method returns a forward cursor over the documents.
+    pub fn into_cursor_and_fields_index(self) -> (DocumentsBatchCursor<R>, DocumentsBatchIndex) {
+        let DocumentsBatchReader { cursor, fields_index } = self;
+        let mut cursor = DocumentsBatchCursor { cursor };
+        cursor.reset();
+        (cursor, fields_index)
+    }
+}
+
+/// A forward cursor over the documents in a `DocumentsBatchReader`.
+pub struct DocumentsBatchCursor<R> {
+    cursor: grenad::ReaderCursor<R>,
+}
+
+impl<R> DocumentsBatchCursor<R> {
+    /// Resets the cursor to be able to read from the start again.
+    pub fn reset(&mut self) {
+        self.cursor.reset();
+    }
+}
+
+impl<R: io::Read + io::Seek> DocumentsBatchCursor<R> {
+    /// Returns a single document from the database.
+    pub fn get(
+        &mut self,
+        offset: u32,
+    ) -> Result<Option<&KvReader<FieldId>>, DocumentsBatchCursorError> {
+        match self.cursor.move_on_key_equal_to(offset.to_be_bytes())? {
+            Some((key, value)) if key != DOCUMENTS_BATCH_INDEX_KEY => Ok(Some(value.into())),
+            _otherwise => Ok(None),
+        }
+    }
+
+    /// Returns the next document, starting from the first one. Subsequent calls to
+    /// `next_document` advance the document reader until all the documents have been read.
+    pub fn next_document(
+        &mut self,
+    ) -> Result<Option<&KvReader<FieldId>>, DocumentsBatchCursorError> {
+        match self.cursor.move_on_next()? {
+            Some((key, value)) if key != DOCUMENTS_BATCH_INDEX_KEY => Ok(Some(value.into())),
+            _otherwise => Ok(None),
+        }
+    }
+}
+
+/// The possible error thrown by the `DocumentsBatchCursor` when iterating on the documents.
+#[derive(Debug)]
+pub enum DocumentsBatchCursorError {
+    Grenad(grenad::Error),
+    SerdeJson(serde_json::Error),
+}
+
+impl From<grenad::Error> for DocumentsBatchCursorError {
+    fn from(error: grenad::Error) -> DocumentsBatchCursorError {
+        DocumentsBatchCursorError::Grenad(error)
+    }
+}
+
+impl From<serde_json::Error> for DocumentsBatchCursorError {
+    fn from(error: serde_json::Error) -> DocumentsBatchCursorError {
+        DocumentsBatchCursorError::SerdeJson(error)
+    }
+}
+
+impl error::Error for DocumentsBatchCursorError {}
+
+impl fmt::Display for DocumentsBatchCursorError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            DocumentsBatchCursorError::Grenad(e) => e.fmt(f),
+            DocumentsBatchCursorError::SerdeJson(e) => e.fmt(f),
+        }
+    }
+}

crates/milli/src/documents/serde_impl.rs

@@ -0,0 +1,76 @@
+use std::fmt;
+use std::io::Write;
+
+use serde::de::{DeserializeSeed, MapAccess, SeqAccess, Visitor};
+
+use super::Error;
+use crate::documents::DocumentsBatchBuilder;
+use crate::Object;
+
+macro_rules! tri {
+    ($e:expr) => {
+        match $e {
+            Ok(r) => r,
+            Err(e) => return Ok(Err(e.into())),
+        }
+    };
+}
+
+pub struct DocumentVisitor<'a, W> {
+    inner: &'a mut DocumentsBatchBuilder<W>,
+    object: Object,
+}
+
+impl<'a, W> DocumentVisitor<'a, W> {
+    pub fn new(inner: &'a mut DocumentsBatchBuilder<W>) -> Self {
+        DocumentVisitor { inner, object: Object::new() }
+    }
+}
+
+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 = Result<(), Error>;
+
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: SeqAccess<'de>,
+    {
+        while let Some(v) = seq.next_element_seed(&mut *self)? {
+            tri!(v)
+        }
+
+        Ok(Ok(()))
+    }
+
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: MapAccess<'de>,
+    {
+        self.object.clear();
+        while let Some((key, value)) = map.next_entry()? {
+            self.object.insert(key, value);
+        }
+
+        tri!(self.inner.append_json_object(&self.object));
+
+        Ok(Ok(()))
+    }
+
+    fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "a documents, or a sequence of documents.")
+    }
+}
+
+impl<'a, 'de, W> DeserializeSeed<'de> for &mut DocumentVisitor<'a, W>
+where
+    W: Write,
+{
+    type Value = Result<(), Error>;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        deserializer.deserialize_map(self)
+    }
+}