Adding the option to implement custom methods in abstract ModelSchema subclasses that cannot be instantiated and thus they don't have to undergo the strict checks that regular ModelSchemata need to fulfill.

Closes !62

Author: mikulas-mrva

djantic/main.py

@@ -57,6 +57,9 @@ def __new__(
                         f"{exc} (Is `Config` class defined?)"
                     )
 
+                if getattr(config, "abstract", False):
+                    continue
+
                 include = getattr(config, "include", None)
                 exclude = getattr(config, "exclude", None)
 
@@ -165,6 +168,12 @@ class ModelSchema(BaseModel, metaclass=ModelSchemaMetaclass):
     class Config:
         orm_mode = True
 
+    def __init__(self, **data):
+        if getattr(self.Config, "abstract", False):
+            raise ConfigError("Abstract ModelSchema cannot be instantiated.")
+
+        super().__init__(**data)
+
     @classmethod
     def schema_json(
         cls,

docs/usage.md

@@ -40,6 +40,33 @@ class UserSchema(ModelSchema):
 
 Once defined, the `UserSchema` can be used to perform various functions on the underlying Django model object, such as generating JSON schemas or exporting serialized instance data.
 
+### Custom subclasses
+
+Abstract subclasses can be defined to implement methods over for a number of ModelSchemata, not that they cannot be instantiated by themselves.
+
+```python
+from typing import Optional
+from django.db.models import Model
+from djantic import ModelSchema
+from myapp.models import User
+
+class BaseModelSchema(ModelSchema):
+    class Config:
+        model: Optional[Model] = None
+        abstract = True
+
+    def to_django(self) -> Model:
+        if self.Config.model is not None:
+            return self.Config.model.objects.create(**self.dict())
+        raise NotImplementedError()
+
+class CreateUserSchema(BaseModelSchema):
+    class Config:
+        model = User
+        
+```
+
+
 ### Basic schema usage
 
 The `UserSchema` above can be used to generate a JSON schema using Pydantic's [schema](https://pydantic-docs.helpmanual.io/usage/schema/) method: