django-cqrs/docs/track_fields_changes.md

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](https://django-model-utils.readthedocs.io/en/latest/utilities.html#field-tracker)
utility class from the
[django-model-utils](https://github.com/jazzband/django-model-utils)
library.