Bugfix/jsonloader metadata (#9793)

Hi,

  - Description: 
    - Solves the issue #6478. 
    - Includes some additional rework on the `JSONLoader` class:
      - Getting metadata is decoupled from `_get_text`
- Validating metadata_func is perform now by `_validate_metadata_func`,
instead of `_validate_content_key`
  - Issue: #6478 
  - Dependencies: NA
  - Tag maintainer: @hwchase17

libs/langchain/langchain/document_loaders/json_loader.py

@@ -76,24 +76,20 @@ class JSONLoader(BaseLoader):
         # and prevent the user from getting a cryptic error later on.
         if self._content_key is not None:
             self._validate_content_key(data)
+        if self._metadata_func is not None:
+            self._validate_metadata_func(data)
 
         for i, sample in enumerate(data, len(docs) + 1):
-            metadata = dict(
-                source=str(self.file_path),
-                seq_num=i,
+            text = self._get_text(sample=sample)
+            metadata = self._get_metadata(
+                sample=sample, source=str(self.file_path), seq_num=i
             )
-            text = self._get_text(sample=sample, metadata=metadata)
             docs.append(Document(page_content=text, metadata=metadata))
 
-    def _get_text(self, sample: Any, metadata: dict) -> str:
+    def _get_text(self, sample: Any) -> str:
         """Convert sample to string format"""
         if self._content_key is not None:
             content = sample.get(self._content_key)
-            if self._metadata_func is not None:
-                # We pass in the metadata dict to the metadata_func
-                # so that the user can customize the default metadata
-                # based on the content of the JSON object.
-                metadata = self._metadata_func(sample, metadata)
         else:
             content = sample
 
@@ -112,6 +108,20 @@ class JSONLoader(BaseLoader):
         else:
             return str(content) if content is not None else ""
 
+    def _get_metadata(
+        self, sample: Dict[str, Any], **additional_fields: Any
+    ) -> Dict[str, Any]:
+        """
+        Return a metadata dictionary base on the existence of metadata_func
+        :param sample: single data payload
+        :param additional_fields: key-word arguments to be added as metadata values
+        :return:
+        """
+        if self._metadata_func is not None:
+            return self._metadata_func(sample, additional_fields)
+        else:
+            return additional_fields
+
     def _validate_content_key(self, data: Any) -> None:
         """Check if a content key is valid"""
         sample = data.first()
@@ -127,6 +137,10 @@ class JSONLoader(BaseLoader):
                     with the key `{self._content_key}`"
             )
 
+    def _validate_metadata_func(self, data: Any) -> None:
+        """Check if the metadata_func output is valid"""
+
+        sample = data.first()
         if self._metadata_func is not None:
             sample_metadata = self._metadata_func(sample, {})
             if not isinstance(sample_metadata, dict):

libs/langchain/tests/unit_tests/document_loaders/test_json_loader.py

@@ -244,7 +244,7 @@ def test_load_empty_jsonlines(mocker: MockerFixture) -> None:
         ),
     ),
 )
-def test_json_meta(
+def test_json_meta_01(
     patch_func: str, patch_func_value: Any, kwargs: Dict, mocker: MockerFixture
 ) -> None:
     mocker.patch("builtins.open", mocker.mock_open())
@@ -270,3 +270,52 @@ def test_json_meta(
     result = loader.load()
 
     assert result == expected_docs
+
+
+@pytest.mark.parametrize(
+    "patch_func,patch_func_value,kwargs",
+    (
+        # JSON content.
+        (
+            "pathlib.Path.read_text",
+            '[{"text": "value1"}, {"text": "value2"}]',
+            {"jq_schema": ".[]", "content_key": "text"},
+        ),
+        # JSON Lines content.
+        (
+            "pathlib.Path.open",
+            io.StringIO(
+                """
+                        {"text": "value1"}
+                        {"text": "value2"}
+                        """
+            ),
+            {"jq_schema": ".", "content_key": "text", "json_lines": True},
+        ),
+    ),
+)
+def test_json_meta_02(
+    patch_func: str, patch_func_value: Any, kwargs: Dict, mocker: MockerFixture
+) -> None:
+    mocker.patch("builtins.open", mocker.mock_open())
+    mocker.patch(patch_func, return_value=patch_func_value)
+
+    file_path = "/workspaces/langchain/test.json"
+    expected_docs = [
+        Document(
+            page_content="value1",
+            metadata={"source": file_path, "seq_num": 1, "x": "value1-meta"},
+        ),
+        Document(
+            page_content="value2",
+            metadata={"source": file_path, "seq_num": 2, "x": "value2-meta"},
+        ),
+    ]
+
+    def metadata_func(record: Dict, metadata: Dict) -> Dict:
+        return {**metadata, "x": f"{record['text']}-meta"}
+
+    loader = JSONLoader(file_path=file_path, metadata_func=metadata_func, **kwargs)
+    result = loader.load()
+
+    assert result == expected_docs