Fetchable

Fetchable is a Swift protocol extension to make Core Data NSManagedObject subclasses more generic (for macOS and iOS). It adds static methods for NSManagedObject subclasses to insert, fetch and delete objects without adding extra code to the subclasses except an enum to specify the sorting attribute keys.

Requirements:

• Swift 4.1
• Xcode 9+
• iOS 8.0+ / macOS 10.10+

Usage:

• Add Fetchable.swift to your project and make all NSManagedObject subclasses adopt Fetchable.

• Add an enum AttributeName to each NSManagedObject subclass to specify the sorting attribute keys for example

    enum AttributeName : String { case name }
    
  

• Fetchable requires a reference to the NSManagedObjectContext instance.

  • If the project uses the default implementation of the Core Data stack in AppDelegate you are done.
  • If the Core Data stack is not located in AppDelegate add a computed read-only property managedObjectContext in AppDelegate and return the reference to the managed object context.
  • If you are using Application Extensions which lacks an AppDelegate class change the reference directly in the Fetchable.swift file.

---

The default method to fetch data is (assuming there is a NSManagedObject subclass Foo)

do {
    let objects = try Foo.objects()
} catch {
    print(error)
}

It returns a non-optional array of Foo objects (no type cast needed).
All fetch methods can throw by passing through the Core Data error.

---

The objects can be sorted in three ways by

1. Passing one attribute key (default direction is ascending)

   let objects = try Foo.objects(sortedBy : .name)
   let objects = try Foo.objects(sortedBy : .index, ascending: false)
   

2. Passing an (variadic) array of tuples representing the key and ascending parameters of a sort descriptor respectively

   let objects = try Foo.objects(sortedBy : (.name, true), (.index, false))
   

3. Passing an array of NSSortDescriptor instances for more advanced sorting

   let objects = try Foo.objects(sortedBy : [NSSortDescriptor(... , NSSortDescriptor(...])
   

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Other (optional) parameters are

• A predicate

  let objects = try Foo.objects(for : NSPredicate(format...)
  

• A fetch limit

  let objects = try Foo.objects(fetchLimit : 2)
  

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A compound filter can be

• let objects = try Foo.objects(for : NSPredicate(format...), sortedBy: .name, fetchLimit : 5)

This is much more convenient than creating the request, predicate and sort descriptor(s) manually.

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There are also corresponding methods to return a single (optional) object

let object = try Foo.object()

and a method to get the number of found objects

let numberOfObjects = try Foo.objectCount()

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The methods to insert a new object, get the entity description and delete all objects are very simple, too.

• let newFoo = Foo.insertNewObject()
• let entityDescription = Foo.entityDescription
• Foo.deleteAll()