Add base_class validation similar to _validate_base_class to bare…

… `generate` calls (#1453)

* Add base_class validation similar to _validate_base_class to bare generate calls

* Remove set default base_class

---------

Co-authored-by: Kyle Bebak <kyle@elementaryml.com>
Co-authored-by: Koudai Aono <koxudaxi@gmail.com>

datamodel_code_generator/__init__.py

@@ -224,7 +224,7 @@ def generate(
     output: Optional[Path] = None,
     output_model_type: DataModelType = DataModelType.PydanticBaseModel,
     target_python_version: PythonVersion = PythonVersion.PY_37,
-    base_class: str = DEFAULT_BASE_CLASS,
+    base_class: str = '',
     additional_imports: Optional[List[str]] = None,
     custom_template_dir: Optional[Path] = None,
     extra_template_data: Optional[DefaultDict[str, Dict[str, Any]]] = None,

tests/data/expected/main/main_generate_non_pydantic_output/output.py

@@ -0,0 +1,12 @@
+# generated by datamodel-codegen:
+#   filename:  simple_string.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass
+class Model:
+    s: str

tests/data/jsonschema/simple_string.json

@@ -0,0 +1,6 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema",
+  "type": "object",
+  "properties": {"s": {"type": ["string"]}},
+  "required": ["s"]
+}

tests/test_main.py

@@ -12,7 +12,13 @@
 from freezegun import freeze_time
 from packaging import version
 
-from datamodel_code_generator import InputFileType, chdir, generate, inferred_message
+from datamodel_code_generator import (
+    DataModelType,
+    InputFileType,
+    chdir,
+    generate,
+    inferred_message,
+)
 from datamodel_code_generator.__main__ import Exit, main
 
 try:
@@ -2694,6 +2700,26 @@ def test_main_generate():
         )
 
 
+@freeze_time('2019-07-26')
+def test_main_generate_non_pydantic_output():
+    """
+    See https://github.com/koxudaxi/datamodel-code-generator/issues/1452.
+    """
+    with TemporaryDirectory() as output_dir:
+        output_file: Path = Path(output_dir) / 'output.py'
+        input_ = (JSON_SCHEMA_DATA_PATH / 'simple_string.json').relative_to(Path.cwd())
+        assert not input_.is_absolute()
+        generate(
+            input_=input_,
+            input_file_type=InputFileType.JsonSchema,
+            output=output_file,
+            output_model_type=DataModelType.DataclassesDataclass,
+        )
+
+        file = EXPECTED_MAIN_PATH / 'main_generate_non_pydantic_output' / 'output.py'
+        assert output_file.read_text() == file.read_text()
+
+
 @freeze_time('2019-07-26')
 def test_main_generate_from_directory():
     with TemporaryDirectory() as output_dir: