fix: respect nullable on array items with --strict-nullable (#2713)

Author: koxudaxi

src/datamodel_code_generator/parser/jsonschema.py

@@ -1068,7 +1068,10 @@ def _get_data_type(type_: str, format__: str) -> DataType:
                 data_types=[_get_data_type(t, obj.format or "default") for t in obj.type if t != "null"],
                 is_optional="null" in obj.type,
             )
-        return _get_data_type(obj.type, obj.format or "default")
+        data_type = _get_data_type(obj.type, obj.format or "default")
+        if self.strict_nullable and obj.nullable:
+            return self.data_type(data_types=[data_type], is_optional=True)
+        return data_type
 
     def get_ref_data_type(self, ref: str) -> DataType:
         """Get a data type from a reference string."""

tests/data/expected/main/jsonschema/nullable_array_items_strict_nullable.py

@@ -0,0 +1,14 @@
+# generated by datamodel-codegen:
+#   filename:  nullable_array_items.yaml
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel
+
+
+class Model(BaseModel):
+    list1: list[str | None]
+    list2: list[int | None]
+    list3: list[str]
+    nested_list: list[list[float | None]]

tests/data/jsonschema/nullable_array_items.yaml

@@ -0,0 +1,27 @@
+properties:
+  list1:
+    type: array
+    items:
+      type: string
+      nullable: true
+  list2:
+    type: array
+    items:
+      type: integer
+      nullable: true
+  list3:
+    type: array
+    items:
+      type: string
+  nested_list:
+    type: array
+    items:
+      type: array
+      items:
+        type: number
+        nullable: true
+required:
+  - list1
+  - list2
+  - list3
+  - nested_list

tests/main/jsonschema/test_main_jsonschema.py

@@ -4518,3 +4518,20 @@ def test_main_allof_root_model_constraints_none(output_file: Path) -> None:
         expected_file="allof_root_model_constraints.py",
         extra_args=["--allof-merge-mode", "none"],
     )
+
+
+@pytest.mark.benchmark
+def test_main_nullable_array_items_strict_nullable(output_file: Path) -> None:
+    """Test nullable array items with strict-nullable flag (issue #1815)."""
+    run_main_and_assert(
+        input_path=JSON_SCHEMA_DATA_PATH / "nullable_array_items.yaml",
+        output_path=output_file,
+        input_file_type="jsonschema",
+        assert_func=assert_file_content,
+        expected_file="nullable_array_items_strict_nullable.py",
+        extra_args=[
+            "--strict-nullable",
+            "--output-model-type",
+            "pydantic_v2.BaseModel",
+        ],
+    )