Fix snake_case generation (#1037)

datamodel_code_generator/reference.py

@@ -127,7 +127,7 @@ def context_variable(
         setter(previous_value)
 
 
-_UNDER_SCORE_1: Pattern[str] = re.compile(r'(.)([A-Z][a-z]+)')
+_UNDER_SCORE_1: Pattern[str] = re.compile(r'([^_])([A-Z][a-z]+)')
 _UNDER_SCORE_2: Pattern[str] = re.compile('([a-z0-9])([A-Z])')
 
 

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

@@ -0,0 +1,17 @@
+# generated by datamodel-codegen:
+#   filename:  snake_case.json
+#   timestamp: 2019-07-26T00:00:00+00:00
+
+from __future__ import annotations
+
+from pydantic import BaseModel, Field
+
+
+class Model(BaseModel):
+    snake_case: str
+    camel_case: str = Field(..., alias='camelCase')
+    kebab_case: str = Field(..., alias='kebab-case')
+    pascal_case: str = Field(..., alias='PascalCase')
+    upper_case: str = Field(..., alias='UPPER_CASE')
+    dev_info: str = Field(..., alias='Dev_Info')
+    clone_device: str = Field(..., alias='CLONE_Device')

tests/data/json/snake_case.json

@@ -0,0 +1,9 @@
+{
+    "snake_case": "Snake case",
+    "camelCase": "Camel case",
+    "kebab-case": "Kebab case",
+    "PascalCase": "Pascal case",
+    "UPPER_CASE": "Upper case",
+    "Dev_Info": "example 1",
+    "CLONE_Device": "example 2"
+}

tests/test_main.py

@@ -4567,3 +4567,29 @@ def test_main_use_default_kwarg():
         )
     with pytest.raises(SystemExit):
         main()
+
+
+@freeze_time('2019-07-26')
+def test_main_json_snake_case_field():
+    with TemporaryDirectory() as output_dir:
+        output_file: Path = Path(output_dir) / 'output.py'
+        return_code: Exit = main(
+            [
+                '--input',
+                str(JSON_DATA_PATH / 'snake_case.json'),
+                '--output',
+                str(output_file),
+                '--input-file-type',
+                'json',
+                '--snake-case-field',
+            ]
+        )
+        assert return_code == Exit.OK
+        assert (
+            output_file.read_text()
+            == (
+                EXPECTED_MAIN_PATH / 'main_json_snake_case_field' / 'output.py'
+            ).read_text()
+        )
+    with pytest.raises(SystemExit):
+        main()