Django : What is the role of ModelState?

django, django-models, python

Solution

From the Django source code, _state is an instance variable defined in each Model instance that is an instance of `ModelState` that is defined as:

class ModelState(object):
    """
    A class for storing instance state
    """
    def __init__(self, db=None):
        self.db = db
        # If true, uniqueness validation checks will consider this a new, as-yet-unsaved object.
        # Necessary for correct validation of new instances of objects with explicit (non-auto) PKs.
        # This impacts validation only; it has no effect on the actual save.
        self.adding = True

So basically this instance variable is used to know if the `Model` instance was already written to a `db` (knowing that Django support multiple db backends) and to hold the `db` used, this instance variable attribute `adding` is set to false after saving the model instance, and it's used mostly (as the comment in the code above) for validating if the primary keys is unique.

Problem

Sorry for not being this as programming question, but this caught my eye when I was trying to introspect my class objects. I found this ``` {'user_id': 1, '_state': <django.db.models.base.ModelState object at 0x10ac2a750>, 'id': 2, 'playlist_id': 8} ``` What is the role of `_state` and what `ModelState` does?

Original source