A description of an attribute of a Core Data entity.


@interface NSAttributeDescription : NSPropertyDescription


NSAttributeDescription inherits from NSPropertyDescription, which provides most of the basic behavior. Instances of NSAttributeDescription are used to describe attributes, as distinct from relationships. The class adds the ability to specify the attribute type, and to specify a default value. In a managed object model, you must specify the type of all attributes—you can only use the undefined attribute type (NSUndefinedAttributeType) for transient attributes.

Editing Attribute Descriptions

Attribute descriptions are editable until they are used by an object graph manager. This allows you to create or modify them dynamically. However, once a description is used (when the managed object model to which it belongs is associated with a persistent store coordinator), it must not (indeed cannot) be changed. This is enforced at runtime: any attempt to mutate a model or any of its sub-objects after the model is associated with a persistent store coordinator causes an exception to be thrown. If you need to modify a model that is in use, create a copy, modify the copy, and then discard the objects with the old model.


Getting and Setting Type Information


The type of the attribute.


The name of the class used to represent the attribute.

Getting and Setting the Default Value


The default value of the attribute.

Supporting Versioning


The version hash for the attribute.

Transforming the Attribute Value


The name of the transformer used to transform the attribute value.

Specifying External Binary Storage


A Boolean value that indicates whether the attribute allows external binary storage.

Tracking Persistent History


A Boolean value that indicates whether the attribute records its value in the persistent history transaction for a managed object’s deletion.


Defining Attribute Types


The possible types of Core Data attributes.


See Also

Attributes and Relationships


A description of a property of a Core Data entity.


The possible types of Core Data attributes.


A description of a relationship of a Core Data entity.

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