Replace SnippetObjectType with SnippetInterface

Fixes #386

API clients could use a field on snippet objects to determine the type
of snippet they are looking at. Therefore, we change the snippet type to
an interface, similar to the page interface, so it can expose a new
field called `snippetType`.

docs/general-usage/graphql-types.rst

@@ -102,33 +102,6 @@ The following fields are returned:
     fileHash: String
 
 
-
-SnippetObjectType
-^^^^^^^^^^^^^^^^^
-
-You won't see much of ``SnippetObjectType`` as it's only a Union type that
-groups all your Snippet models together. You can query all the available snippets
-under the ``snippets`` field under the root Query, The query is similar to
-an interface but ``SnippetObjectType`` doesn't provide any fields itself.
-
-When snippets are attached to Pages you interact with your generated type itself
-as opposed to an interface or base type.
-
-An example of querying all snippets:
-
-::
-
-    query {
-        snippets {
-            ...on Advert {
-                id
-                url
-                text
-            }
-        }
-    }
-
-
 SettingObjectType
 ^^^^^^^^^^^^^^^^^
 

docs/general-usage/interfaces.rst

@@ -50,7 +50,7 @@ the name of the model:
     }
 
 You can change the default ``PageInterface`` to your own interface by changing the
-:ref:`PAGE_INTERFACE<page interface settings>` setting.
+:ref:`PAGE_INTERFACE<page interface setting>` setting.
 
 As mentioned above there is both a plural ``pages`` and singular ``page``
 field on the root Query type that returns a ``PageInterface``.
@@ -107,6 +107,35 @@ in the interface:
 
 
 
+``SnippetInterface``
+--------------------
+
+``SnippetInterface`` is the default interface for all Wagtail snippet models. It is accessible throught the
+``snippets`` field on the root query type. It exposes the following fields:
+
+::
+
+    snipeptType: String!
+
+An example of querying all snippets:
+
+::
+
+    query {
+        snippets {
+            snippetType
+            ...on Advert {
+                id
+                url
+                text
+            }
+        }
+    }
+
+You can change the default ``SnippetInterface`` to your own interface by changing the
+:ref:`SNIPPET_INTERFACE<snippet interface setting>` setting.
+
+
 Adding your own interfaces
 --------------------------
 

docs/getting-started/settings.rst

@@ -141,10 +141,10 @@ Limit the maximum number of items that ``QuerySetList`` and ``PaginatedQuerySet`
 Default: ``100``
 
 
-.. _page interface settings:
+Wagtail model interfaces
+^^^^^^^^^^^^^^^^^^^^^^^^
 
-Wagtail Page interface
-^^^^^^^^^^^^^^^^^^^^^^
+.. _page interface setting:
 
 ``PAGE_INTERFACE``
 ******************
@@ -153,3 +153,14 @@ Used to construct the schema for Wagtail Page-derived models. It can be overridd
 page models.
 
 Default: ``grapple.types.interfaces.PageInterface``
+
+
+.. _snippet interface setting:
+
+``SNIPPET_INTERFACE``
+*********************
+
+Used to construct the schema for Wagtail snippet models. It can be overridden to provide a custom interface for all
+snippet models.
+
+Default: ``grapple.types.interfaces.SnippetInterface``

grapple/actions.py

@@ -27,6 +27,7 @@
 from .types.images import ImageObjectType, ImageRenditionObjectType
 from .types.pages import Page, get_page_interface
 from .types.rich_text import RichText as RichTextType
+from .types.snippets import get_snippet_interface
 from .types.streamfield import generate_streamfield_union
 
 
@@ -612,7 +613,7 @@ def register_snippet_model(cls: Type[models.Model], type_prefix: str):
         return
 
     # Create a GQL type that implements Snippet Interface
-    snippet_node_type = build_node_type(cls, type_prefix, None)
+    snippet_node_type = build_node_type(cls, type_prefix, get_snippet_interface())
 
     if snippet_node_type:
         registry.snippets[cls] = snippet_node_type

grapple/settings.py

@@ -29,6 +29,7 @@
     "MAX_PAGE_SIZE": 100,
     "RICHTEXT_FORMAT": "html",
     "PAGE_INTERFACE": "grapple.types.interfaces.PageInterface",
+    "SNIPPET_INTERFACE": "grapple.types.interfaces.SnippetInterface",
 }
 
 # List of settings that have been deprecated

grapple/types/interfaces.py

@@ -209,3 +209,18 @@ def resolve_raw_value(self, info, **kwargs):
             return self.value.source
 
         return self.value
+
+
+def get_snippet_interface():
+    return import_string(grapple_settings.SNIPPET_INTERFACE)
+
+
+class SnippetInterface(graphene.Interface):
+    snippet_type = graphene.String(required=True)
+
+    @classmethod
+    def resolve_type(cls, instance, info, **kwargs):
+        return registry.snippets[type(instance)]
+
+    def resolve_snippet_type(self, info, **kwargs):
+        return self.__class__.__name__

grapple/types/snippets.py

@@ -1,49 +1,19 @@
 import graphene
 
 from ..registry import registry
-
-
-class SnippetTypes:
-    # SnippetObjectType class can only be created if
-    # registry.snippets.types is non-empty, and should only be created
-    # once (graphene complains if we register multiple type classes
-    # with identical names)
-    _SnippetObjectType = None
-
-    @classmethod
-    def get_object_type(cls):
-        if cls._SnippetObjectType is None and registry.snippets:
-
-            class SnippetObjectType(graphene.Union):
-                class Meta:
-                    types = registry.snippets.types
-
-            cls._SnippetObjectType = SnippetObjectType
-        return cls._SnippetObjectType
+from .interfaces import get_snippet_interface
 
 
 def SnippetsQuery():
-    SnippetObjectType = SnippetTypes.get_object_type()
-
-    if SnippetObjectType is not None:
-
-        class Mixin:
-            snippets = graphene.List(graphene.NonNull(SnippetObjectType), required=True)
-            # Return all snippets.
-
-            def resolve_snippets(self, info, **kwargs):
-                snippet_objects = []
-                for snippet in registry.snippets:
-                    for object in snippet._meta.model.objects.all():
-                        snippet_objects.append(object)
-
-                return snippet_objects
-
-        return Mixin
+    class Mixin:
+        snippets = graphene.List(graphene.NonNull(get_snippet_interface), required=True)
 
-    else:
+        def resolve_snippets(self, info, **kwargs):
+            snippet_objects = []
+            for snippet in registry.snippets:
+                for object in snippet._meta.model.objects.all():
+                    snippet_objects.append(object)
 
-        class Mixin:
-            pass
+            return snippet_objects
 
-        return Mixin
+    return Mixin

grapple/types/streamfield.py

@@ -353,8 +353,7 @@ def resolve_items(self, info, **kwargs):
 def register_streamfield_blocks():
     from .documents import get_document_type
     from .images import get_image_type
-    from .interfaces import get_page_interface
-    from .snippets import SnippetTypes
+    from .interfaces import get_page_interface, get_snippet_interface
 
     class PageChooserBlock(graphene.ObjectType):
         page = graphene.Field(get_page_interface(), required=False)
@@ -391,20 +390,17 @@ def resolve_image(self, info, **kwargs):
         }
     )
 
-    SnippetObjectType = SnippetTypes.get_object_type()
-    if SnippetObjectType is not None:
+    class SnippetChooserBlock(graphene.ObjectType):
+        snippet = graphene.Field(get_snippet_interface(), required=False)
 
-        class SnippetChooserBlock(graphene.ObjectType):
-            snippet = graphene.Field(SnippetObjectType, required=False)
-
-            class Meta:
-                interfaces = (StreamFieldInterface,)
+        class Meta:
+            interfaces = (StreamFieldInterface,)
 
-            def resolve_snippet(self, info, **kwargs):
-                return self.value
+        def resolve_snippet(self, info, **kwargs):
+            return self.value
 
-        registry.streamfield_blocks.update(
-            {
-                wagtail.snippets.blocks.SnippetChooserBlock: SnippetChooserBlock,
-            }
-        )
+    registry.streamfield_blocks.update(
+        {
+            wagtail.snippets.blocks.SnippetChooserBlock: SnippetChooserBlock,
+        }
+    )

tests/settings_custom_interfaces.py

@@ -2,3 +2,4 @@
 
 
 GRAPPLE["PAGE_INTERFACE"] = "testapp.interfaces.CustomPageInterface"  # noqa: F405
+GRAPPLE["SNIPPET_INTERFACE"] = "testapp.interfaces.CustomSnippetInterface"  # noqa: F405

tests/test_grapple.py

@@ -10,7 +10,7 @@
 from django.db import connection
 from django.test import RequestFactory, TestCase, override_settings
 from graphene.test import Client
-from testapp.factories import BlogPageFactory
+from testapp.factories import AdvertFactory, BlogPageFactory
 from testapp.models import GlobalSocialMediaSettings, HomePage, SocialMediaSettings
 from wagtail.documents import get_document_model
 from wagtail.models import Page, Site
@@ -1579,3 +1579,28 @@ def test_query_single_setting_without_site_filter_and_multiple_sites(self):
                 "data": {"setting": None},
             },
         )
+
+
+class SnippetsTest(BaseGrappleTest):
+    def setUp(self):
+        super().setUp()
+        self.factory = RequestFactory()
+        self.advert = AdvertFactory()
+
+    def test_snippets(self):
+        query = """
+        {
+            snippets {
+                snippetType
+            }
+        }
+        """
+
+        executed = self.client.execute(query)
+
+        self.assertEqual(type(executed["data"]), dict)
+        self.assertEqual(type(executed["data"]["snippets"]), list)
+        self.assertEqual(type(executed["data"]["snippets"][0]), dict)
+
+        snippets_data = executed["data"]["snippets"]
+        self.assertEqual(snippets_data[0]["snippetType"], "Advert")

tests/test_interfaces.py

@@ -5,9 +5,13 @@
 from django.test import override_settings, tag
 from test_grapple import BaseGrappleTestWithIntrospection
 from testapp.factories import AdditionalInterfaceBlockFactory, BlogPageFactory
-from testapp.interfaces import CustomPageInterface
+from testapp.interfaces import CustomPageInterface, CustomSnippetInterface
 
-from grapple.types.interfaces import PageInterface, get_page_interface
+from grapple.types.interfaces import (
+    PageInterface,
+    get_page_interface,
+    get_snippet_interface,
+)
 
 
 @skipIf(
@@ -41,6 +45,12 @@ def test_schema_with_default_page_interface(self):
     def test_get_page_interface_with_custom_page_interface(self):
         self.assertIs(get_page_interface(), CustomPageInterface)
 
+    @override_settings(
+        GRAPPLE={"SNIPPET_INTERFACE": "testapp.interfaces.CustomSnippetInterface"}
+    )
+    def test_get_snippet_interface_with_custom_page_interface(self):
+        self.assertIs(get_snippet_interface(), CustomSnippetInterface)
+
     def test_streamfield_block_with_additional_interface(self):
         query = """
         query($id: ID) {
@@ -86,7 +96,7 @@ def test_schema_for_snippet_with_graphql_interface(self):
         results = self.introspect_schema_by_type("Advert")
         self.assertListEqual(
             sorted(results["data"]["__type"]["interfaces"], key=lambda x: x["name"]),
-            [{"name": "AdditionalInterface"}],
+            [{"name": "AdditionalInterface"}, {"name": "SnippetInterface"}],
         )
 
     def test_schema_for_django_model_with_graphql_interfaces(self):
@@ -108,3 +118,10 @@ def test_schema_with_custom_page_interface(self):
         self.assertListEqual(
             results["data"]["__type"]["interfaces"], [{"name": "CustomPageInterface"}]
         )
+
+    def test_schema_with_custom_snippet_interface(self):
+        results = self.introspect_schema_by_type("Person")
+        self.assertListEqual(
+            results["data"]["__type"]["interfaces"],
+            [{"name": "CustomSnippetInterface"}],
+        )

tests/testapp/interfaces.py

@@ -1,6 +1,6 @@
 import graphene
 
-from grapple.types.interfaces import PageInterface
+from grapple.types.interfaces import PageInterface, SnippetInterface
 
 
 class AdditionalInterface(graphene.Interface):
@@ -9,3 +9,10 @@ class AdditionalInterface(graphene.Interface):
 
 class CustomPageInterface(PageInterface):
     custom_text = graphene.String()
+
+
+class CustomSnippetInterface(SnippetInterface):
+    custom_text = graphene.String()
+
+    def resolve_custom_text(self, info, **kwargs):
+        return str(self)