Class

NSRelationshipDescription

A description of a relationship of a Core Data entity.

Declaration

@interface NSRelationshipDescription : NSPropertyDescription

Overview

NSRelationshipDescription extends NSPropertyDescription to describe features appropriate to relationships, including cardinality (the number of objects allowed in the relationship), the destination entity, and delete rules.

Cardinality

The maximum and minimum counts for a relationship indicate the number of objects referenced (1/1 for a to-one relationship, 0 means undefined). The counts are only enforced if the relationship value in the containing object is not nil. That is, optional relationships may have zero objects in the relationship, which might be less than the minimum count.

Editing Relationship Descriptions

Relationship 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.

Topics

Managing Type Information

destinationEntity

The entity description of the receiver's destination.

inverseRelationship

The relationship that represents the inverse of the receiver.

Getting and Setting Delete Rules

deleteRule

The delete rule of the receiver.

Handling Cardinality

maxCount

The maximum count of the receiver.

minCount

The minimum count of the receiver.

toMany

A Boolean value that indicates whether the receiver represents a to-many relationship.

Controlling Ordering

ordered

Returns a Boolean value that indicates whether the receiver describes an ordered relationship.

Supporting Versioning

versionHash

The version hash for the receiver.

Configuring Delete Rules

NSDeleteRule

These constants define what happens to relationships when an object is deleted.

Relationships

See Also

Attributes and Relationships

NSPropertyDescription

A description of a property of a Core Data entity.

NSAttributeDescription

A description of an attribute of a Core Data entity.

NSAttributeType

The possible types of Core Data attributes.

NSDerivedAttributeDescription

A description of an attribute of a Core Data entity that derives its value from one or more other properties.