NSPredicate with multiple arguments and “AND behaviour”

Question

I have a function which fetches those objects from a particular entity that fulfill a specified criterion:

func fetchWithPredicate(entityName: String, argume         


        

Answer 1

To create a predicate (with a variable number of expressions) dynamically, use NSCompoundPredicate, e.g.

let predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)

where subPredicates is a [NSPredicate] array, and each subpredicate is created from the provided arguments in a loop with

NSPredicate(format: "%K == %@", key, value)

Something like this (untested):

func fetchWithPredicate(entityName: String, argumentArray: [NSObject])  -> [NSManagedObject]  {

    var subPredicates : [NSPredicate] = []
    for i in 0.stride(to: argumentArray.count, by: 2) {
        let key = argumentArray[i]
        let value = argumentArray[i+1]
        let subPredicate = NSPredicate(format: "%K == %@", key, value)
        subPredicates.append(subPredicate)
    }

    let fetchRequest = NSFetchRequest(entityName: entityName)
    fetchRequest.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: subPredicates)

    // ...
}