Add serialize_class attribute to support using custom Serializer

Author: nxet

README.md

@@ -11,6 +11,7 @@ this mixin definitely suits you.
 - [Advanced usage](#Advanced-usage)
 - [Custom formats](#Custom-formats)
 - [Custom types](#Custom-types)
+- [Custom Serializer](#Custom-serializer)
 - [Timezones](#Timezones)
 - [Troubleshooting](#Troubleshooting)
 - [Tests](#Tests)
@@ -304,6 +305,27 @@ Unfortunately you can not access formats or tzinfo in that functions.
 I'll implement this logic later if any of users needs it.
 
 
+# Custom Serializer
+To have full control over the Serializer, you can define your own subclass with custom logic, and then configure the mixin to use it.
+```python
+from sqlalchemy_serializer import Serializer, SerializerMixin
+
+
+class CustomSerializer(Serializer):
+
+    def serialize_model(self, value) -> dict:
+        """Custom override adding special case for a complex model."""
+        if isinstance(value, ComplexModel):
+            return complex_logic(value)
+        return super().serialize_model(value)
+
+
+class CustomSerializerMixin(SerializerMixin):
+
+    serialize_class = CustomSerializer
+```
+
+
 # Timezones
 To keep `datetimes` consistent its better to store it in the database normalized to **UTC**.
 But when you return response, sometimes (mostly in web, mobile applications can do it themselves)

sqlalchemy_serializer/serializer.py

@@ -123,7 +123,7 @@ def fork(self, key: str) -> "Serializer":
         Return new serializer for a key
         :return: serializer
         """
-        serializer = Serializer(**self.opts._asdict())
+        serializer = self.__class__(**self.opts._asdict())
         serializer.set_serialization_depth(self.serialization_depth + 1)
         serializer.schema = self.schema.fork(key=key)
 
@@ -233,6 +233,9 @@ class SerializerMixin:
     some extra serialization logic
     """
 
+    # Default Serializer class
+    serialize_class: Serializer = Serializer
+
     # Default exclusive schema.
     # If left blank, serializer becomes greedy and takes all SQLAlchemy-model's attributes
     serialize_only: tuple = ()
@@ -292,7 +295,7 @@ def to_dict(
         :param tzinfo: datetime.tzinfo converts datetimes to local user timezone
         :return: data: dict
         """
-        s = Serializer(
+        s = self.serialize_class(
             date_format=date_format or self.date_format,
             datetime_format=datetime_format or self.datetime_format,
             time_format=time_format or self.time_format,