Check if attribute exists

Is there better way rather than to fetch with predicate and see the number of results in order to check that the attribute exists when adding it into managed context? I'm trying to make开发者_运维技巧 an attribute unique for given entity...

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I think you may have scrambled your nomenclature. You don't add attributes to context. You add managed objects which are defined by entities which have attributes. You could be asking about two different types of test.

If you're asking whether a means exist of testing if a managed object already exist with the exact same attributes of the one you planning on inserting, the answer is no. Since entities can be arbitrarily complex and since it takes only literally one bit different to make them logically distinct, there is no means of testing whether two objects are logically identical i.e. have the same attributes and relationships, without fetching them and testing them.

If you're asking whether you can test for a unique value of an attribute of a particular entity then you can. First you fetch on a property using [NSFetchRequest setProperty:] and then set you're predicate for the sought value. When walking relationships, you can use the Set and Array Operators to find managed objects with unique values.