![]() ![]() Instead call the general method validateValue:forKey:error: with the appropriate key. If you do implement custom validation methods, you should typically not invoke them directly. Instead implement methods of the form validate:error. If you want to implement logic in addition to the constraints you provide in the managed object model, do not override validateValue:forKey:error. NSManagedObject provides consistent hooks for implementing property (and interproperty) values. The NSKeyValueCoding protocol specifies the validateValue:forKey:error: method to provide general support for validation methods in a similar way to that in which valueForKey: provides support for accessor methods. Implementing Custom Property-Level Validation The ability to work with managed objects when they are not in a valid state also underpins the idea of a managed object context representing a scratch pad-in general you can bring managed objects onto the scratch pad and edit them however you wish before ultimately committing the changes or discarding them. If managed objects were required to be always in a valid state, it would among other things force a particular workflow on the user. ![]() Other times it makes sense to wait until a unit of work is completed before validation takes place. Sometimes it is useful to validate changes as soon as they are made and to report errors immediately. The validation constraints are applied by Core Data only during a save operation or upon request (you can invoke the validation methods directly at any time it makes sense for your application flow). Moreover, at various times, inconsistencies are expected to arise in managed objects and object graphs.Īn in-memory object can temporarily become inconsistent. For example, a value binding for a text field might have its “validates immediately” option enabled. How to validate is a model decision, when to validate is a user interface or controller-level decision. To validate combinations of values (such as an array) and relationships, see Implementing Custom Interproperty Validation. ![]() If you do want to customize validation of individual properties, you use standard validation methods as defined by the NSKeyValueCoding protocol and described in Implementing Custom Property-Level Validation. You can also specify constraints on relationships, such as making them mandatory or unable exceed a certain number. You can specify maximum and minimum values for numeric and date attributes, maximum and minimum lengths for string attributes, and a regular expression that a string attribute must match. Core Data, on the other hand, allows you to put validation logic into the managed object model and specify most common constraints as opposed to writing validation logic in your code. However, it requires you to write code for all the constraints you want to apply. Cocoa provides a basic infrastructure for model value validation. ![]()
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