Core Data Helpers

CoreData+Extensions.swift

//The following code depends on this:
//https://gist.github.com/sisoje/f1444dff45618938ce81324a81316690#file-nspredicate-keypath-operators-swift

import CoreData

extension NSManagedObject {
    static var entityName: String {
        return entity().name!
    }
}

extension NSManagedObjectContext {
    func insertObject<MO: NSManagedObject>() -> MO {
        guard let obj = NSEntityDescription
            .insertNewObject(forEntityName: MO.entityName, into: self) as? MO else {
                fatalError("Entity \(MO.entityName) does not correspond to \(MO.self)")
        }

        return obj
    }

    func findFirst<MO: NSManagedObject, T: Equatable>(_ keyPath: KeyPath<MO, T>, _ value: T) throws -> MO? {
        return try findFirst(keyPath == value)
    }

    func findFirst<MO: NSManagedObject>(_ predicate: NSPredicate) throws -> MO? {
        let fetchRequest: NSFetchRequest<MO> = MO.fetchRequest() as! NSFetchRequest<MO>
        fetchRequest.fetchLimit = 1
        fetchRequest.predicate = predicate
        return try fetch(fetchRequest).first
    }

    func findFirstOrCreate<MO: NSManagedObject, T: Equatable>(_ keyPath: ReferenceWritableKeyPath<MO, T>, _ value: T) throws -> MO {
        if let existing = try findFirst(keyPath, value) {
            return existing
        }

        let object = MO(context: self)
        object[keyPath: keyPath] = value
        return object
    }

    func findAll<MO: NSManagedObject, T: Equatable>(_ keyPath: KeyPath<MO, T>, _ value: T) throws -> [MO] {
        let fetchRequest: NSFetchRequest<MO> = MO.fetchRequest() as! NSFetchRequest<MO>
        fetchRequest.predicate = keyPath == value
        return try fetch(fetchRequest)
    }
}

extension NSFetchRequest {
    @objc func filter(_ aPredicate: NSPredicate) -> NSFetchRequest<ResultType> {
        if let existingPredicate = predicate {
            self.predicate = NSCompoundPredicate(andPredicateWithSubpredicates: [existingPredicate, aPredicate])
        } else {
            self.predicate = aPredicate
        }

        return self
    }
}