By default, django-cqrs serializes all the fields declared
for the master model or the subset specified by the
Sometimes you want to customize how the master model will be serialized, for example including some other fields from related models.
When there are master models with related entities in CQRS_SERIALIZER, it's important to have operations within atomic transactions. CQRS sync will happen on transaction commit. Please, avoid saving master model within transaction more then once to reduce syncing and potential racing on replica side. Updating of related model won't trigger CQRS automatic synchronization for master model. This needs to be done manually.
In this case you can control how an instance of the master model is serialized providing a serializer class to be used for that:
class MyMasterModel(MasterMixin): CQRS_ID = 'my_model' CQRS_SERIALIZER = 'mymodule.serializers.MyMasterModelSerializer' @classmethod def relate_cqrs_serialization(cls, queryset): # Optimize related models fetching here return queryset
If you would to serialize fields from related models, you can optimize
database access overriding the
relate_cqrs_serialization method using
methods of the QuerySet
If you provide a serializer to customize serialization, you must handle yourself deserialization for the replica model.
class MyReplicaModel(ReplicaMixin): CQRS_ID = 'my_model' CQRS_CUSTOM_SERIALIZATION = True # bypass default deserialization. @classmethod def cqrs_create(cls, sync, mapped_data, previous_data=None, meta=None): # Custom deserialization logic here pass def cqrs_update(self, sync, mapped_data, previous_data=None, meta=None): # Custom deserialization logic here pass
A serializer class must follow these rules:
- The constructor must accept the model instance as the only positional argument
- Must have a
dataproperty that returns a python dictionary as the instance representation.
If your service exposes a RESTful API written using Django REST framework you can use your model serializers out of the box also for CQRS serialization.