Fix empty list default for GraphQL list fields

Author: koxudaxi

src/datamodel_code_generator/model/pydantic/base_model.py

@@ -126,9 +126,23 @@ def _get_strict_field_constraint_value(self, constraint: str, value: Any) -> Any
             return value
         return int(value)
 
-    def _get_default_as_pydantic_model(self) -> str | None:
+    def _get_default_as_pydantic_model(self) -> str | None:  # noqa: PLR0911, PLR0912
         if isinstance(self.default, WrappedDefault):
             return f"lambda :{self.default!r}"
+        # Handle the case where self.data_type.is_list is True directly (e.g., GraphQL)
+        if self.data_type.is_list and len(self.data_type.data_types) == 1:
+            data_type_child = self.data_type.data_types[0]
+            if (
+                data_type_child.reference
+                and isinstance(data_type_child.reference.source, BaseModelBase)
+                and isinstance(self.default, list)
+            ):
+                if not self.default:
+                    return STANDARD_LIST
+                return (  # pragma: no cover
+                    f"lambda :[{data_type_child.alias or data_type_child.reference.source.class_name}."
+                    f"{self._PARSE_METHOD}(v) for v in {self.default!r}]"
+                )
         for data_type in self.data_type.data_types or (self.data_type,):
             # TODO: Check nested data_types
             if data_type.is_dict:

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

@@ -7,15 +7,26 @@
 from typing import Literal
 
 from pydantic import BaseModel, Field
+from typing_extensions import TypeAliasType
 
+Boolean = TypeAliasType("Boolean", bool)
+"""
+The `Boolean` scalar type represents `true` or `false`.
+"""
 
-class Container(BaseModel):
-    name: str
-    typename__: Literal['Container'] | None = Field('Container', alias='__typename')
 
+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 PodSpec(BaseModel):
-    container_list: list[Container] = Field(default_factory=list)
-    container_list_or_none: list[Container | None] = Field(default_factory=list)
-    container_or_none_list_or_none: list[Container | None] | None = Field(default_factory=list)
-    typename__: Literal['PodSpec'] | None = Field('PodSpec', alias='__typename')
+
+class TagInput(BaseModel):
+    name: String
+    value: String
+    typename__: Literal['TagInput'] | None = Field('TagInput', alias='__typename')
+
+
+class ModelInput(BaseModel):
+    tags: list[TagInput] | None = Field(default_factory=list)
+    typename__: Literal['ModelInput'] | None = Field('ModelInput', alias='__typename')

tests/data/graphql/empty_list_default.graphql

@@ -1,10 +1,8 @@
-
-input Container {
+input TagInput {
   name: String!
+  value: String!
 }
 
-input PodSpec {
-  container_list: [Container!]! = []
-  container_list_or_none: [Container]! = []
-  container_or_none_list_or_none: [Container] = []
+input ModelInput {
+  tags: [TagInput!] = []
 }

tests/main/graphql/test_main_graphql.py

@@ -12,7 +12,7 @@
     EXPECTED_GRAPHQL_PATH,
     GRAPHQL_DATA_PATH,
     LEGACY_BLACK_SKIP,
-    run_main_and_assert
+    run_main_and_assert,
 )
 from tests.main.graphql.conftest import assert_file_content