Fix Length constraints for object-valued Marshmallow fields

CHANGELOG.rst

@@ -6,6 +6,8 @@ unreleased
 
 Bug fixes:
 
+- Use object property counts for ``Length`` validators on ``Dict`` and
+  non-many ``Nested`` fields.
 - Recognize ``trace`` operations defined in view docstrings, instead of
   silently dropping them (:pr:`1059`).
   Thanks :user:`binggao1230` for the PR.

src/apispec/ext/marshmallow/field_converter.py

@@ -364,11 +364,16 @@ def field2length(
             )
         ]
 
-        is_array = isinstance(
-            field, (marshmallow.fields.Nested, marshmallow.fields.List)
-        )
-        min_attr = "minItems" if is_array else "minLength"
-        max_attr = "maxItems" if is_array else "maxLength"
+        if isinstance(field, marshmallow.fields.Dict) or (
+            isinstance(field, marshmallow.fields.Nested)
+            and not isinstance(field, marshmallow.fields.Pluck)
+            and not field.schema.many
+        ):
+            min_attr, max_attr = "minProperties", "maxProperties"
+        elif isinstance(field, (marshmallow.fields.Nested, marshmallow.fields.List)):
+            min_attr, max_attr = "minItems", "maxItems"
+        else:
+            min_attr, max_attr = "minLength", "maxLength"
 
         equal_list = [
             validator.equal for validator in validators if validator.equal is not None

tests/test_ext_marshmallow_openapi.py

@@ -676,6 +676,20 @@ class ValidationSchema(Schema):
         custom_list_length = CustomList(
             fields.Str, validate=validate.Length(min=1, max=10)
         )
+        dict_length = fields.Dict(validate=validate.Length(min=1, max=10))
+        dict_equal_length = fields.Dict(validate=validate.Length(equal=5))
+        nested_length = fields.Nested(
+            CategorySchema, validate=validate.Length(min=1, max=10)
+        )
+        nested_many_length = fields.Nested(
+            CategorySchema, many=True, validate=validate.Length(min=1, max=10)
+        )
+        nested_inherited_many_length = fields.Nested(
+            CategorySchema(many=True), validate=validate.Length(min=1, max=10)
+        )
+        pluck_length = fields.Pluck(
+            CategorySchema, "name", validate=validate.Length(min=1, max=10)
+        )
         string_length = fields.Str(validate=validate.Length(min=1, max=10))
         custom_field_length = CustomStringField(validate=validate.Length(min=1, max=10))
         multiple_lengths = fields.Str(
@@ -703,6 +717,11 @@ class ValidationSchema(Schema):
             ("multiple_ranges", {"minimum": 3, "maximum": 7}),
             ("list_length", {"minItems": 1, "maxItems": 10}),
             ("custom_list_length", {"minItems": 1, "maxItems": 10}),
+            ("dict_length", {"minProperties": 1, "maxProperties": 10}),
+            ("dict_equal_length", {"minProperties": 5, "maxProperties": 5}),
+            ("nested_length", {"minProperties": 1, "maxProperties": 10}),
+            ("nested_many_length", {"minItems": 1, "maxItems": 10}),
+            ("nested_inherited_many_length", {"minItems": 1, "maxItems": 10}),
             ("string_length", {"minLength": 1, "maxLength": 10}),
             ("custom_field_length", {"minLength": 1, "maxLength": 10}),
             ("multiple_lengths", {"minLength": 3, "maxLength": 7}),
@@ -717,3 +736,11 @@ def test_properties(self, field, properties, spec):
         for attr, expected_value in properties.items():
             assert attr in result
             assert result[attr] == expected_value
+
+    def test_pluck_length_does_not_add_object_properties(self, spec):
+        spec.components.schema("Validation", schema=self.ValidationSchema)
+        result = get_schemas(spec)["Validation"]["properties"]["pluck_length"]
+
+        assert result["type"] == "string"
+        assert "minProperties" not in result
+        assert "maxProperties" not in result