Django : What is the role of ModelState?
Question:
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?
Answers:
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.
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?
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.