Use metaclass to maintain the mapping between serializers and models

Author: paul

README.md

@@ -2,7 +2,7 @@
 
 We need something a little meaningful so the example consists of some simple models in a class heirarchy and an associated heirarchy of model serializers<sup id="n1">[1](#f1).
 
-The ??first commit shows how serializers need to be accessed for the model classes in order to serialize/deserialize model data.
+The first commit shows how serializers need to be accessed for the model classes in order to serialize/deserialize model data.
 
 Maintaining the serializer_class_map quickly becomes cumbersome.
 
@@ -17,7 +17,7 @@ but this is repeating the association because its already present in the Meta (s
 
 We could add a serializer_class field to the models but this is coupling the serializers to the models in an undesirable way. We want to keep the serialization concern to our serializers.
 
-So how about a metaclass?
+##So how about a metaclass?
 If we specify a metaclass for our serializers we can update the serializer_class_map whenever we create a new serializer class.
 
 ## Footnotes

example.py

@@ -25,10 +25,25 @@ class Car(Model):
 
 
 # Serializers are responsible for serializing some model class:
-class Serializer(object):
+class MappedSerializerClass(type):
+    serializer_class_map = {}
+
     class Meta:
         model_class = None
 
+    def __init__(cls, *args, **kwargs) -> None:
+        super().__init__(*args, **kwargs)
+        model_class = cls.Meta.model_class
+        if model_class:
+            MappedSerializerClass.serializer_class_map[model_class] = cls
+
+
+def get_serializer_class(model):
+    return MappedSerializerClass.serializer_class_map[type(model)]
+
+
+class Serializer(object, metaclass=MappedSerializerClass):
+
     def __init__(self, model=None) -> None:
         super().__init__()
         self.model = model
@@ -50,6 +65,8 @@ def serialize(self):
 
 
 class VehicleSerializer(ModelSerializer):
+    class Meta:
+        model_class = None
 
     def serialize(self):
         return {**super().serialize(), 'travels_on': self.model.travels_on}
@@ -80,11 +97,6 @@ def serialize(self):
                         'ship1': {'class': Ship},
                         'car1': {'class': Car}}
 
-serializer_class_map = {Model: ModelSerializer,
-                        Building: BuildingSerializer,
-                        Car: CarSerializer,
-                        Ship: ShipSerializer}
-
 
 def make_model(name, spec):
     model_class = spec.pop('class')
@@ -94,10 +106,6 @@ def make_model(name, spec):
 models = {name: make_model(name, spec) for name, spec in serialized_models_in.items()}
 
 
-def get_serializer_class(model):
-    return serializer_class_map[type(model)]
-
-
 serialized_models_out = {name: get_serializer_class(model)(model).serialize() for name, model in models.items()}