Keep track of changes to fields

In some circumstances, you want to keep track of changes made on some fields of the master model.

django-cqrs can send previous values of the tracked fields to replicas.

To do so, you can use the CQRS_TRACKED_FIELDS attribute to specify which fields to track:

class MyMasterModel(MasterMixin):

    CQRS_ID = 'my_model'
    CQRS_TRACKED_FIELDS = ('char_field', 'parent', 'status')


    char_field = models.CharField(max_length=100)
    status = models.CharField(max_length=15, choices=STATUSES)

    parent = models.ForeignKey(ParentMode, on_delete=models.CASCADE)

This way, you can override the cqrs_save and apply your persistence logic based o tracked fields before accessing your database:

class MyReplicaModel(ReplicaMixin):

    CQRS_ID = 'my_model'

    @classmethod
    def cqrs_save(cls, master_data, previous_data=None, sync=False):
        # Custom logic based on previous_data here.
        pass

Note

The fields tracking features honors the CQRS_MAPPING attribute.

Note

The fields tracking features relies on the FieldTracker utility class from the django-model-utils library.