# validateValue(_:forKey:) Validates a property value for a given key. ``` func validateValue(_ value: AutoreleasingUnsafeMutablePointer, forKey key: String) throws ``` ## Parameters `value` A pointer to an object. `key` The name of one of the receiver’s properties. ## Discussion This method is responsible for two things: coercing the value into an appropriate type for the object, and validating it according to the object’s rules. The default implementation provided by `NSManagedObject` consults the object’s entity description to coerce the value and to check for basic errors, such as a null value when that isn’t allowed and the length of strings when a field width is specified for the attribute. It then searches for a method of the form `validate:error:` and invokes it if it exists. You can implement methods of the form `validate:error:` to perform validation that is not possible using the constraints available in the property description. If it finds an unacceptable value, your validation method should return and in `error` an `NSError` object that describes the problem. For more details, see Managed Object Validation. For inter-property validation (to check for combinations of values that are invalid), see [`validateForUpdate()`](/documentation/CoreData/NSManagedObject/validateForUpdate()) and related methods. --- 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)