Fix deprecation warnings around "copy_on_model_validation" (#927)

* Fix deprecation warnings

* Support old pydantic version

* Add packaging to deps

Co-authored-by: Koudai Aono <koxudaxi@gmail.com>

datamodel_code_generator/reference.py

@@ -29,6 +29,8 @@
 )
 
 import inflect
+import pydantic
+from packaging import version
 from pydantic import BaseModel, validator
 
 from datamodel_code_generator import cached_property
@@ -92,7 +94,11 @@ def validate_original_name(cls, v: Any, values: Dict[str, Any]) -> str:
     class Config:
         arbitrary_types_allowed = True
         keep_untouched = (cached_property,)
-        copy_on_model_validation = False
+        copy_on_model_validation = (
+            False
+            if version.parse(pydantic.VERSION) < version.parse('1.9.2')
+            else 'none'
+        )
 
     @property
     def short_name(self) -> str:

datamodel_code_generator/types.py

@@ -21,6 +21,8 @@
     Union,
 )
 
+import pydantic
+from packaging import version
 from pydantic import StrictBool, StrictInt, StrictStr, create_model
 
 from datamodel_code_generator import Protocol, runtime_checkable
@@ -64,8 +66,12 @@ def module_name(self) -> str:
 
 class DataType(_BaseModel):
     class Config:
-        extra = "forbid"
-        copy_on_model_validation = False
+        extra = 'forbid'
+        copy_on_model_validation = (
+            False
+            if version.parse(pydantic.VERSION) < version.parse('1.9.2')
+            else 'none'
+        )
 
     type: Optional[str]
     reference: Optional[Reference]