The fields to fetch for the requested records.
- iOS 8.0+
- macOS 10.10+
- tvOS 9.0+
- watchOS 3.0+
Use this property to limit the amount of data retrieved for each record during the fetch operation. This property contains an array of
NSString objects, each of which contains the name of a field from the target records. When you retrieve a given record, only fields whose names match one of the keys in this property are included in the returned record. The default value of this property is
nil, which causes all keys of the record to be fetched.
Because the records you fetch can be of different types, the array should contain the merged set of all field names for the requested records and should include at least one field name from each record type.
If you intend to specify a value other than
nil, do so before executing the operation or submitting the operation object to a queue.