Fast-field based implementation of ExistsQuery (#2160)

Adds an implementation of ExistsQuery that takes advantage of fast fields.

Fixes #2159

Author: imotov

src/fastfield/readers.rs

@@ -234,6 +234,22 @@ impl FastFieldReaders {
         Ok(dynamic_column_handle_opt)
     }
 
+    /// Returning all `dynamic_column_handle`.
+    pub fn dynamic_column_handles(
+        &self,
+        field_name: &str,
+    ) -> crate::Result<Vec<DynamicColumnHandle>> {
+        let Some(resolved_field_name) = self.resolve_field(field_name)? else {
+            return Ok(Vec::new());
+        };
+        let dynamic_column_handles = self
+            .columnar
+            .read_columns(&resolved_field_name)?
+            .into_iter()
+            .collect();
+        Ok(dynamic_column_handles)
+    }
+
     #[doc(hidden)]
     pub async fn list_dynamic_column_handles(
         &self,
@@ -338,6 +354,8 @@ impl FastFieldReaders {
 
 #[cfg(test)]
 mod tests {
+    use columnar::ColumnType;
+
     use crate::schema::{JsonObjectOptions, Schema, FAST};
     use crate::{Document, Index};
 
@@ -417,4 +435,45 @@ mod tests {
             Some("_dyna\u{1}notinschema\u{1}attr\u{1}color".to_string())
         );
     }
+
+    #[test]
+    fn test_fast_field_reader_dynamic_column_handles() {
+        let mut schema_builder = Schema::builder();
+        let id = schema_builder.add_u64_field("id", FAST);
+        let json = schema_builder.add_json_field("json", FAST);
+        let schema = schema_builder.build();
+        let index = Index::create_in_ram(schema);
+        let mut index_writer = index.writer_for_tests().unwrap();
+        index_writer
+            .add_document(doc!(id=> 1u64, json => json!({"foo": 42})))
+            .unwrap();
+        index_writer
+            .add_document(doc!(id=> 2u64, json => json!({"foo": true})))
+            .unwrap();
+        index_writer
+            .add_document(doc!(id=> 3u64, json => json!({"foo": "bar"})))
+            .unwrap();
+        index_writer.commit().unwrap();
+        let reader = index.reader().unwrap();
+        let searcher = reader.searcher();
+        let reader = searcher.segment_reader(0u32);
+        let fast_fields = reader.fast_fields();
+        let id_columns = fast_fields.dynamic_column_handles("id").unwrap();
+        assert_eq!(id_columns.len(), 1);
+        assert_eq!(id_columns.first().unwrap().column_type(), ColumnType::U64);
+
+        let foo_columns = fast_fields.dynamic_column_handles("json.foo").unwrap();
+        assert_eq!(foo_columns.len(), 3);
+        assert!(foo_columns
+            .iter()
+            .any(|column| column.column_type() == ColumnType::I64));
+        assert!(foo_columns
+            .iter()
+            .any(|column| column.column_type() == ColumnType::Bool));
+        assert!(foo_columns
+            .iter()
+            .any(|column| column.column_type() == ColumnType::Str));
+
+        println!("*** {:?}", fast_fields.columnar().list_columns());
+    }
 }