Fix GraphQL interface MRO ordering for multiple inheritance

Author: koxudaxi

src/datamodel_code_generator/parser/graphql.py

@@ -421,6 +421,50 @@ def parse_field(
             use_serialization_alias=self.use_serialization_alias,
         )
 
+    @staticmethod
+    def _sort_interfaces_for_mro(
+        interfaces: list[graphql.GraphQLInterfaceType],
+    ) -> list[graphql.GraphQLInterfaceType]:
+        """Sort interfaces so that subclasses come before their parent classes.
+
+        This ensures valid Python MRO (Method Resolution Order) when a class
+        implements multiple interfaces where some interfaces extend others.
+
+        For example, if Notification implements Node, and a class implements
+        both Node and Notification, the order should be [Notification, Node]
+        not [Node, Notification].
+        """
+        if len(interfaces) <= 1:
+            return interfaces
+
+        # Build a set of all interface names for quick lookup
+        interface_names = {i.name for i in interfaces}
+
+        # Get all ancestors for each interface (only considering interfaces in our list)
+        def get_ancestors(iface: graphql.GraphQLInterfaceType) -> set[str]:
+            """Get all ancestor interface names that are in our interface list."""
+            ancestors: set[str] = set()
+            to_visit = list(getattr(iface, "interfaces", []))
+            while to_visit:
+                parent = to_visit.pop()
+                if parent.name in interface_names and parent.name not in ancestors:
+                    ancestors.add(parent.name)
+                    to_visit.extend(getattr(parent, "interfaces", []))
+            return ancestors
+
+        # Build ancestor map
+        ancestor_map = {i.name: get_ancestors(i) for i in interfaces}
+
+        # Sort: interfaces with ancestors in the list should come before those ancestors
+        # Use stable sort with custom key
+        def sort_key(iface: graphql.GraphQLInterfaceType) -> tuple[int, str]:
+            # Count how many other interfaces this one is an ancestor of
+            # Interfaces that are ancestors of more others should come later
+            ancestor_count = sum(1 for other in interfaces if iface.name in ancestor_map[other.name])
+            return (ancestor_count, iface.name)
+
+        return sorted(interfaces, key=sort_key)
+
     def parse_object_like(
         self,
         obj: graphql.GraphQLInterfaceType | graphql.GraphQLObjectType | graphql.GraphQLInputObjectType,
@@ -448,7 +492,8 @@ def parse_object_like(
 
         base_classes = []
         if hasattr(obj, "interfaces"):
-            base_classes = [self.references[i.name] for i in obj.interfaces]  # ty: ignore
+            sorted_interfaces = self._sort_interfaces_for_mro(list(obj.interfaces))  # ty: ignore
+            base_classes = [self.references[i.name] for i in sorted_interfaces]
 
         data_model_type = self._create_data_model(
             reference=self.references[obj.name],

tests/data/expected/main/graphql/interface_mro.py

@@ -0,0 +1,56 @@
+# generated by datamodel-codegen:
+#   filename:  interface_mro.graphql
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Annotated, Literal
+
+from pydantic import BaseModel, Field
+from typing_extensions import TypeAliasType
+
+Boolean = TypeAliasType("Boolean", bool)
+"""
+The `Boolean` scalar type represents `true` or `false`.
+"""
+
+
+ID = TypeAliasType("ID", str)
+"""
+The `ID` scalar type represents a unique identifier, often used to refetch an object or as key for a cache. The ID type appears in a JSON response as a String; however, it is not intended to be human-readable. When expected as an input type, any string (such as `"4"`) or integer (such as `4`) input value will be accepted as an ID.
+"""
+
+
+String = TypeAliasType("String", str)
+"""
+The `String` scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text.
+"""
+
+
+class Entity(BaseModel):
+    id: ID
+    typename__: Annotated[Literal['Entity'] | None, Field(alias='__typename')] = (
+        'Entity'
+    )
+
+
+class Node(BaseModel):
+    id: ID
+    typename__: Annotated[Literal['Node'] | None, Field(alias='__typename')] = 'Node'
+
+
+class Notification(Node):
+    id: ID
+    read_at: Annotated[String | None, Field(alias='readAt')] = None
+    typename__: Annotated[Literal['Notification'] | None, Field(alias='__typename')] = (
+        'Notification'
+    )
+
+
+class CustomerNeedNotification(Entity, Notification, Node):
+    customer: String | None = None
+    id: ID
+    read_at: Annotated[String | None, Field(alias='readAt')] = None
+    typename__: Annotated[
+        Literal['CustomerNeedNotification'] | None, Field(alias='__typename')
+    ] = 'CustomerNeedNotification'

tests/data/expected/main/graphql/union_class_name_prefix.py

@@ -0,0 +1,67 @@
+# generated by datamodel-codegen:
+#   filename:  union_class_name_prefix.graphql
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from typing import Annotated, Literal, Union
+
+from pydantic import BaseModel, Field
+from typing_extensions import TypeAliasType
+
+FooBoolean = TypeAliasType("FooBoolean", bool)
+"""
+The `Boolean` scalar type represents `true` or `false`.
+"""
+
+
+FooID = TypeAliasType("FooID", str)
+"""
+The `ID` scalar type represents a unique identifier, often used to refetch an object or as key for a cache. The ID type appears in a JSON response as a String; however, it is not intended to be human-readable. When expected as an input type, any string (such as `"4"`) or integer (such as `4`) input value will be accepted as an ID.
+"""
+
+
+FooInt = TypeAliasType("FooInt", int)
+"""
+The `Int` scalar type represents non-fractional signed whole numeric values. Int can represent values between -(2^31) and 2^31 - 1.
+"""
+
+
+FooString = TypeAliasType("FooString", str)
+"""
+The `String` scalar type represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text.
+"""
+
+
+class FooIResource(BaseModel):
+    id: FooID
+    typename__: Annotated[Literal['IResource'] | None, Field(alias='__typename')] = (
+        'IResource'
+    )
+
+
+class FooCar(FooIResource):
+    id: FooID
+    passenger_capacity: Annotated[FooInt, Field(alias='passengerCapacity')]
+    typename__: Annotated[Literal['Car'] | None, Field(alias='__typename')] = 'Car'
+
+
+class FooEmployee(FooIResource):
+    first_name: Annotated[FooString | None, Field(alias='firstName')] = None
+    id: FooID
+    last_name: Annotated[FooString | None, Field(alias='lastName')] = None
+    typename__: Annotated[Literal['Employee'] | None, Field(alias='__typename')] = (
+        'Employee'
+    )
+
+
+FooResource = TypeAliasType(
+    "FooResource",
+    Union[
+        'FooCar',
+        'FooEmployee',
+    ],
+)
+
+
+FooTechnicalResource = TypeAliasType("FooTechnicalResource", FooCar)

tests/data/graphql/interface_mro.graphql

@@ -0,0 +1,18 @@
+interface Entity {
+    id: ID!
+}
+
+interface Node {
+    id: ID!
+}
+
+interface Notification implements Node {
+    id: ID!
+    readAt: String
+}
+
+type CustomerNeedNotification implements Entity & Node & Notification {
+    id: ID!
+    readAt: String
+    customer: String
+}

tests/data/graphql/union_class_name_prefix.graphql

@@ -0,0 +1,18 @@
+interface IResource {
+    id: ID!
+}
+
+type Employee implements IResource {
+    id: ID!
+    firstName: String
+    lastName: String
+}
+
+type Car implements IResource {
+    id: ID!
+    passengerCapacity: Int!
+}
+
+union Resource = Employee | Car
+
+union TechnicalResource = Car

tests/main/graphql/test_main_graphql.py

@@ -777,6 +777,31 @@ def test_main_graphql_class_name_prefix(output_file: Path) -> None:
     )
 
 
+def test_main_graphql_union_class_name_prefix(output_file: Path) -> None:
+    """Test that union type members get class name prefix applied.
+
+    When using --class-name-prefix, the prefix should be applied to both
+    the union type name and all its member type references.
+
+    This test verifies fix for issue #2939.
+    """
+    run_main_and_assert(
+        input_path=GRAPHQL_DATA_PATH / "union_class_name_prefix.graphql",
+        output_path=output_file,
+        input_file_type="graphql",
+        assert_func=assert_file_content,
+        expected_file="union_class_name_prefix.py",
+        extra_args=[
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+            "--class-name-prefix",
+            "Foo",
+            "--use-annotated",
+            "--snake-case-field",
+        ],
+    )
+
+
 def test_main_graphql_union_snake_case_field(output_file: Path) -> None:
     """Test that union type references are not converted to snake_case."""
     run_main_and_assert(
@@ -789,6 +814,31 @@ def test_main_graphql_union_snake_case_field(output_file: Path) -> None:
     )
 
 
+def test_main_graphql_interface_mro(output_file: Path) -> None:
+    """Test that interface inheritance is ordered correctly for Python MRO.
+
+    When a class implements multiple interfaces where some interfaces extend others,
+    the base classes must be ordered so that subclasses come before their parent classes.
+    For example, if Notification implements Node, and a class implements both
+    Node and Notification, the order should be (Notification, Node) not (Node, Notification).
+
+    This test verifies fix for issue #2938.
+    """
+    run_main_and_assert(
+        input_path=GRAPHQL_DATA_PATH / "interface_mro.graphql",
+        output_path=output_file,
+        input_file_type="graphql",
+        assert_func=assert_file_content,
+        expected_file="interface_mro.py",
+        extra_args=[
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+            "--use-annotated",
+            "--snake-case-field",
+        ],
+    )
+
+
 def test_main_graphql_split_graphql_schemas(output_file: Path) -> None:
     """Test GraphQL code generation with multiple schema files in a directory."""
     run_main_and_assert(