What is a fetched property?
Essence
A fetched property is an entity property in a Core Data model whose value is computed by a query (an NSFetchRequest with a predicate) rather than stored as a relationship. It's a "weak", one-directional relationship: the predicate can refer to the current object's attributes via $FETCH_SOURCE and to external variables via $FETCHED_PROPERTY. The result is always an array (NSArray), even if a single object is found.
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