community[minor]: Fix json._validate_metadata_func() (#22842)

JSONparse, in _validate_metadata_func(), checks the consistency of the
_metadata_func() function. To do this, it invokes it and makes sure it
receives a dictionary in response. However, during the call, it does not
respect future calls, as shown on line 100. This generates errors if,
for example, the function is like this:
```python
        def generate_metadata(json_node:Dict[str,Any],kwargs:Dict[str,Any]) -> Dict[str,Any]:
             return {
                "source": url,
                "row": kwargs['seq_num'],
                "question":json_node.get("question"),
            }
        loader = JSONLoader(
            file_path=file_path,
            content_key="answer",
            jq_schema='.[]',
            metadata_func=generate_metadata,
            text_content=False)
```
To avoid this, the verification must comply with the specifications.
This patch does just that.

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/community/langchain_community/document_loaders/json_loader.py

@@ -157,8 +157,6 @@ 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, index + 1):
             text = self._get_text(sample=sample)
@@ -178,7 +176,7 @@ class JSONLoader(BaseLoader):
         else:
             content = sample
 
-        if self._text_content and not isinstance(content, str):
+        if self._text_content and not isinstance(content, str) and content is not None:
             raise ValueError(
                 f"Expected page_content is string, got {type(content)} instead. \
                     Set `text_content=False` if the desired input for \
@@ -203,7 +201,13 @@ class JSONLoader(BaseLoader):
         :return:
         """
         if self._metadata_func is not None:
-            return self._metadata_func(sample, additional_fields)
+            result = self._metadata_func(sample, additional_fields)
+            if not isinstance(result, dict):
+                raise ValueError(
+                    f"Expected the metadata_func to return a dict but got \
+                                `{type(result)}`"
+                )
+            return result
         else:
             return additional_fields
 
@@ -233,15 +237,3 @@ class JSONLoader(BaseLoader):
                 f"Expected the jq schema to result in a list of objects (dict) \
                     with the key `{self._content_key}` which should be parsable by jq"
             )
-
-    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):
-                raise ValueError(
-                    f"Expected the metadata_func to return a dict but got \
-                        `{type(sample_metadata)}`"
-                )

libs/community/tests/integration_tests/document_loaders/test_json_loader.py

@@ -1,12 +1,20 @@
 from pathlib import Path
+from typing import Dict
 
 from langchain_community.document_loaders import JSONLoader
 
 
+def call_back(sample: Dict, additional_fields: Dict) -> Dict:
+    metadata = additional_fields.copy()
+    metadata["source"] += f"#seq_num={metadata['seq_num']}"
+    return metadata
+
+
 def test_json_loader() -> None:
     """Test unstructured loader."""
     file_path = Path(__file__).parent.parent / "examples/example.json"
-    loader = JSONLoader(str(file_path), ".messages[].content")
+
+    loader = JSONLoader(file_path, ".messages[].content", metadata_func=call_back)
     docs = loader.load()
 
     # Check that the correct number of documents are loaded.