Change format of content of _validation field (#425)

The content of _validation field must to be the string representation of a Python dict instead defaultdict when SPIDERMON_VALIDATION_ADD_ERRORS_TO_ITEMS setting is True.

docs/source/getting-started.rst

@@ -478,8 +478,7 @@ The resulted item will look like this:
 .. code-block:: js
 
     {
-        '_validation': defaultdict(
-            <class 'list'>, {'author_url': ['Invalid URL']}),
+        '_validation': {'author_url': ['Invalid URL']},
          'author': 'Mark Twain',
          'author_url': 'not_a_valid_url',
          'quote': 'Never tell the truth to people who are not worthy of it.',

docs/source/item-validation.rst

@@ -81,7 +81,7 @@ You can change the name of the field by assigning a name to `SPIDERMON_VALIDATIO
 .. code-block:: js
 
     {
-        '_validation': defaultdict(<class 'list'>, {'author_url': ['Invalid URL']}),
+        '_validation': {'author_url': ['Invalid URL']},
         'author': 'C.S. Lewis',
         'author_url': 'invalid_url',
         'quote': 'Some day you will be old enough to start reading fairy tales '

spidermon/contrib/scrapy/pipelines.py

@@ -129,13 +129,16 @@ def find_validators(self, item):
 
     def _add_errors_to_item(self, item: ItemAdapter, errors: Dict[str, str]):
         errors_field_instance = get_nested_attribute(item, self.errors_field)
+
         if errors_field_instance is None:
             errors_field_instance = defaultdict(list)
-            set_nested_attribute(item, self.errors_field, errors_field_instance)
 
         for field_name, messages in errors.items():
             errors_field_instance[field_name] += messages
 
+        # change defaultdict to dict for errors_field_instance
+        set_nested_attribute(item, self.errors_field, dict(errors_field_instance))
+
     def _drop_item(self, item, errors):
         """
         This method drops the item after detecting validation errors. Note

tests/contrib/validation/test_item_validation_pipeline.py

@@ -1,3 +1,4 @@
+from collections import defaultdict
 from dataclasses import dataclass
 
 import pytest
@@ -87,6 +88,7 @@ def test_jsonschema_validation(dummy_schema):
     result_item = pipeline.process_item(dict(item), None)
     assert item != result_item
     assert "_validation" in result_item
+    assert not isinstance(result_item["_validation"], defaultdict)
     assert result_item["_validation"]["foo"] == ["Missing required field"]