[BUGFIX] argilla server: search on chat field when selected (#5504)

# Description
<!-- Please include a summary of the changes and the related issue.
Please also include relevant motivation and context. List any
dependencies that are required for this change. -->

When a chat field is selected for searches, the search returns no
results.

**Type of change**
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PR according to the type of change -->

- Bug fix (non-breaking change which fixes an issue)

**How Has This Been Tested**
<!-- Please add some reference about how your feature has been tested.
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**Checklist**
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account -->

- I added relevant documentation
- I followed the style guidelines of this project
- I did a self-review of my code
- I made corresponding changes to the documentation
- I confirm My changes generate no new warnings
- I have added tests that prove my fix is effective or that my feature
works
- I have added relevant notes to the CHANGELOG.md file (See
https://keepachangelog.com/)

---------

Co-authored-by: José Francisco Calvo <[email protected]>

argilla-server/src/argilla_server/models/database.py

@@ -386,6 +386,11 @@ def is_ready(self):
     def distribution_strategy(self) -> DatasetDistributionStrategy:
         return DatasetDistributionStrategy(self.distribution["strategy"])
 
+    def field_by_name(self, name: str) -> Union["Field", None]:
+        for field in self.fields:
+            if field.name == name:
+                return field
+
     def metadata_property_by_name(self, name: str) -> Union["MetadataProperty", None]:
         for metadata_property in self.metadata_properties:
             if metadata_property.name == name:

argilla-server/src/argilla_server/search_engine/commons.py

@@ -153,7 +153,7 @@ def es_field_for_metadata_property(metadata_property: Union[str, MetadataPropert
 
 
 def es_field_for_record_field(field_name: str) -> str:
-    return f"fields.{field_name or '*'}"
+    return f"fields.{field_name}"
 
 
 def es_field_for_response_property(property: str) -> str:
@@ -647,7 +647,19 @@ def _build_text_query(dataset: Dataset, text: Optional[Union[TextQuery, str]] =
         if isinstance(text, str):
             text = TextQuery(q=text)
 
-        return es_simple_query_string(es_field_for_record_field(text.field), query=text.q)
+        if text.field:
+            field = dataset.field_by_name(text.field)
+            if field is None:
+                raise Exception(f"Field {text.field} not found in dataset {dataset.id}")
+
+            if field.is_chat:
+                field_name = f"{text.field}.*"
+            else:
+                field_name = text.field
+        else:
+            field_name = "*"
+
+        return es_simple_query_string(es_field_for_record_field(field_name), query=text.q)
 
     @staticmethod
     def _mapping_for_fields(fields: List[Field]) -> dict:

argilla-server/tests/unit/search_engine/test_commons.py

@@ -66,6 +66,7 @@
     VectorFactory,
     VectorSettingsFactory,
     ImageFieldFactory,
+    ChatFieldFactory,
 )
 
 
@@ -596,6 +597,28 @@ async def test_search_with_query_string(
 
         assert scores == sorted_scores
 
+    async def test_search_for_chat_field(self, search_engine: BaseElasticAndOpenSearchEngine, opensearch: OpenSearch):
+        chat_field = await ChatFieldFactory.create(name="field")
+
+        dataset = await DatasetFactory.create(fields=[chat_field])
+
+        records = await RecordFactory.create_batch(
+            size=2,
+            dataset=dataset,
+            fields={chat_field.name: [{"role": "user", "content": "Hello world"}, {"role": "bot", "content": "Hi"}]},
+        )
+
+        await refresh_dataset(dataset)
+        await refresh_records(records)
+
+        await search_engine.create_index(dataset)
+        await search_engine.index_records(dataset, records)
+
+        result = await search_engine.search(dataset, query=TextQuery(q="world", field=chat_field.name))
+
+        assert len(result.items) == 2
+        assert result.total == 2
+
     @pytest.mark.parametrize(
         "statuses, expected_items",
         [