# inverse(forRelationshipKey:) For a given key that defines the name of the relationship from the receiver’s class to another class, returns the name of the relationship from the other class to the receiver’s class. ``` func inverse(forRelationshipKey relationshipKey: String) -> String? ``` ## Parameters `relationshipKey` The name of the relationship from the receiver’s class to another class. ## Return Value The name of the relationship that is the inverse of the receiver’s relationship named `relationshipKey`. ## Discussion `NSObject`’s implementation of `inverseForRelationshipKey:` simply invokes `[[self classDescription] inverseForRelationshipKey:relationshipKey]`. To make use of the default implementation, you must therefore implement and register a suitable class description—see . For example, suppose an Employee class has a relationship named `department` to a Department class, and that Department has a relationship called `employees` to Employee. The statement: ```objc employee inverseForRelationshipKey:@"department"]; ``` returns the string `employees`. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)