Fix ambiguity error with Polymorphism candidates (isinstance() proble…

…m) (#691)

* Fix for better Polymorphism support

Right now Polymorphism fails when using something like this (models in sqlalchemy):

models:

```python
class Product(BaseModel):
	discr = Column(String)

	__mapper_args__ = {
		'polymorphic_on': discr,
        'polymorphic_identity': "product"
	}

class VegetableProduct(Product):
	name = Column(String)

    __mapper_args__ = {
		'polymorphic_identity': "vegetable"
	}

class DairyProduct(VegetableProduct):
    __mapper_args__ = {
		'polymorphic_identity': "dairy"
	}
```

mapper:

```python
resource_product = api.model("Product", {
	'discr': fields.String
})

product_mapper = {
	VegetableProduct: api.inherit("Vegetable", resource_product, { 'name': fields.String }),
	DairyProduct: api.inherit("Dairy", resource_product, { 'name': fields.String }),
}

resource_result = api.model("ResourceResult", {
	'products': fields.List(fields.Polymorphism(product_mapper))
})
```

This sparkles error here:

https://github.com/noirbizarre/flask-restplus/blob/master/flask_restplus/fields.py#L682

Because candidates will be: VegetableProduct and DairyProduct, since isinstance() will return True for both classes (I personally surprised it works like this)

Checking by __class__.__name__ removes this error and it works as intended.

I hope my quick fix did not break anything, I'm eager to update it if I don't know, more elegant solution is needed.

* adjusted ambiguity test for new feature

* stricter check for type

* changed to simple class check

* type() check for Polymorphism, adjusted tests

* type() check for Polymorphism, adjusted tests

* removed local dev files

* updated test name, also PR in docblock

flask_restplus/fields.py

@@ -674,7 +674,7 @@ def output(self, key, obj, ordered=False, **kwargs):
         if not hasattr(value, '__class__'):
             raise ValueError('Polymorph field only accept class instances')
 
-        candidates = [fields for cls, fields in iteritems(self.mapping) if isinstance(value, cls)]
+        candidates = [fields for cls, fields in iteritems(self.mapping) if type(value) == cls]
 
         if len(candidates) <= 0:
             raise ValueError('Unknown class: ' + value.__class__.__name__)

tests/test_fields.py

@@ -1177,7 +1177,10 @@ class Child2(object):
         with pytest.raises(ValueError):
             api.marshal({'owner': object()}, thing)
 
-    def test_polymorph_field_ambiguous_mapping(self, api):
+    def test_polymorph_field_does_not_have_ambiguous_mappings(self, api):
+        """
+        Regression test for https://github.com/noirbizarre/flask-restplus/pull/691
+        """
         parent = api.model('Parent', {
             'name': fields.String,
         })
@@ -1201,8 +1204,7 @@ class Child(Parent):
             'owner': fields.Polymorph(mapping),
         })
 
-        with pytest.raises(ValueError):
-            api.marshal({'owner': Child()}, thing)
+        api.marshal({'owner': Child()}, thing)
 
     def test_polymorph_field_required_default(self, api):
         parent = api.model('Person', {

tests/test_swagger.py

@@ -2279,11 +2279,11 @@ def get(self):
         assert path['get']['responses']['200']['schema']['$ref'] == '#/definitions/Output'
 
     def test_polymorph_inherit_list(self, api, client):
-        class Child1:
+        class Child1(object):
             name = 'Child1'
             extra1 = 'extra1'
 
-        class Child2:
+        class Child2(object):
             name = 'Child2'
             extra2 = 'extra2'