All non-deferred fields of the model are updated to the values currently.When this method is called without arguments the If you need to reload a model’s values from the database, you can use the refresh_from_db( using=None, fields=None) ¶ field # Loads the field from the database Model. In this case it would be possible to use a super() call in the
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The example above shows a full from_db() implementation to clarify how that _loaded_values ): raise ValueError ( "Updating the value of creator isn't allowed" ) super (). (This example doesn't # support cases where 'creator_id' is deferred). For example, # prevent changing the creator_id of the model. _loaded_values = dict ( zip ( field_names, values )) return instance def save ( self, * args, ** kwargs ): # Check how the current values differ from. db = db # customization to store the original field values on the instance instance. reverse () values = instance = cls ( * values ) instance. concrete_fields ): values = list ( values ) values.
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In addition to creating the new model, the from_db() method must set theĪdding and db flags in the new instance’s _state attribute.īelow is an example showing how to record the initial values of fields thatįrom django.db.models import DEFERRED def from_db ( cls, db, field_names, values ): # Default implementation of from_db() (subject to change and could # be replaced with super()). In that case, assign a value of django.db.models.DEFERRED If any fields are deferred, they won’t appear inįield_names. That is, the instance can be created byĬls(*values). If all of the model’sįields are present, then values are guaranteed to be in the order Theįield_names are in the same order as the values. Values contains the loaded values for each field in field_names. Is loaded from, field_names contains the names of all loaded fields, and The db argument contains the database alias for the database the model The from_db() method can be used to customize model instance creation Customizing model loading ¶ classmethod Model.
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