Swift wrapper for NSPersistentContainer - Easy Core Data Setup with iOS 10

CoreDataController.swift

//
//  CoreDataController.swift
//
//  Created by Keith Harrison http://useyourloaf.com
//  Copyright (c) 2017 Keith Harrison. All rights reserved.
//
//  Redistribution and use in source and binary forms, with or without
//  modification, are permitted provided that the following conditions are met:
//
//  1. Redistributions of source code must retain the above copyright
//  notice, this list of conditions and the following disclaimer.
//
//  2. Redistributions in binary form must reproduce the above copyright
//  notice, this list of conditions and the following disclaimer in the
//  documentation and/or other materials provided with the distribution.
//
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//  this software without specific prior written permission.
//
//  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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import Foundation
import CoreData

/// `CoreDataController` is a simple wrapper class for setting up
/// and using a Core Data stack.
///
/// Warning: Requires iOS 10 as it depends on the availability of
/// `NSPersistentContainer`.

@available(iOS 10.0, macOS 10.12, watchOS 3.0, tvOS 10.0, *)
public class CoreDataController: NSObject {

    /// The default directory for the persistent stores on the current platform.
    ///
    /// - Returns: An `NSURL` for the directory containing the persistent 
    ///   store(s). If the persistent store does not exist it will be created
    ///   by default in this location when loaded.

    public class func defaultDirectoryURL() -> URL {
        return NSPersistentContainer.defaultDirectoryURL()
    }

    /// A read-only flag indicating if the persistent store is loaded.

    public private (set) var isStoreLoaded = false

    /// The managed object context associated with the main queue (read-only).
    /// To perform tasks on a private background queue see 
    /// `performBackgroundTask:` and `newPrivateContext`.
    ///
    /// The context is configured to be generational and to automatically 
    /// consume save notifications from other contexts.

    public var viewContext: NSManagedObjectContext {
        return persistentContainer.viewContext
    }

    /// The `URL` of the persistent store for this Core Data Stack. If there
    /// is more than one store this property returns the first store it finds.
    /// The store may not yet exist. It will be created at this URL by default 
    /// when first loaded.
    ///
    /// This is a readonly property to create a persistent store in a different
    /// location use `loadStoreAtURL:withCompletionHandler`. To move an existing
    ///  persistent store use 
    /// `replacePersistentStoreAtURL:withPersistentStoreFromURL:`.

    public var storeURL: URL? {
        var url: URL?
        let descriptions = persistentContainer.persistentStoreDescriptions
        if let firstDescription = descriptions.first {
            url = firstDescription.url
        }
        return url
    }

    /// A flag that indicates whether this store is read-only. Set this value
    /// to YES before loading the persistent store if you want a read-only 
    /// store (for example if loading from the application bundle).
    /// Default is false.

    public var isReadOnly = false

    /// A flag that indicates whether the store is added asynchronously.
    /// Set this value before loading the persistent store.
    /// Default is true.

    public var shouldAddStoreAsynchronously = true

    /// A flag that indicates whether the store should be migrated
    /// automatically if the store model version does not match the
    /// coordinators model version.
    /// Set this value before loading the persistent store.
    /// Default is true.

    public var shouldMigrateStoreAutomatically = true

    /// A flag that indicates whether a mapping model should be inferred
    /// when migrating a store.
    /// Set this value before loading the persistent store.
    /// Default is true.

    public var shouldInferMappingModelAutomatically = true

    /// Creates and returns a `CoreDataController` object. This is the designated
    /// initializer for the class. It creates the managed object model,
    /// persistent store coordinator and main managed object context but does
    /// not load the persistent store.
    ///
    /// The managed object model should be in the same bundle as this class.
    ///
    /// - Parameter name: The name of the persistent store.
    ///
    /// - Returns: A `CoreDataController` object or nil if the model
    ///   could not be loaded.

    public init?(name: String) {
        let bundle = Bundle(for: CoreDataController.self)
        guard let mom = NSManagedObjectModel.mergedModel(from: [bundle]) else {
            return nil
        }

        persistentContainer = NSPersistentContainer(name: name, managedObjectModel: mom)
        super.init()
    }

    /// Load the persistent store from the default location.
    ///
    /// - Parameter handler: This handler block is executed on the calling
    ///   thread when the loading of the persistent store has completed.
    ///
    /// To override the default name and location of the persistent store use
    /// `loadStoreAtURL:withCompletionHandler:`.

    public func loadStore(completionHandler: @escaping (Error?) -> Void) {
        loadStore(storeURL: storeURL, completionHandler: completionHandler)
    }

    /// Load the persistent store from a specified location
    ///
    /// - Parameter storeURL: The URL for the location of the persistent
    ///   store. It will be created if it does not exist.
    /// - Parameter handler: This handler block is executed on the calling
    ///   thread when the loading of the persistent store has completed.

    public func loadStore(storeURL: URL?, completionHandler: @escaping (Error?) -> Void) {

        if let storeURL = storeURL ?? self.storeURL {
            let description = storeDescription(with: storeURL)
            persistentContainer.persistentStoreDescriptions = [description]
        }

        persistentContainer.loadPersistentStores { (storeDescription, error) in
            if error == nil {
                self.isStoreLoaded = true
                self.persistentContainer.viewContext.automaticallyMergesChangesFromParent = true
            }

            DispatchQueue.main.async {
                completionHandler(error)
            }
        }
    }

    /// A flag indicating if the persistent store exists at the specified URL.
    ///
    /// - Parameter storeURL: An `NSURL` object for the location of the
    ///   peristent store.
    ///
    /// - Returns: true if a file exists at the specified URL otherwise false.
    ///
    /// - Warning: This method checks if a file exists at the specified 
    ///   location but does not verify if it is a valid persistent store.

    public func persistentStoreExists(at storeURL: URL) -> Bool {
        if storeURL.isFileURL &&
            FileManager.default.fileExists(atPath: storeURL.path) {
            return true
        }
        return false
    }

    /// Destroy a persistent store.
    ///
    /// - Parameter storeURL: An `NSURL` for the persistent store to be 
    ///   destroyed.
    /// - Returns: A flag indicating if the operation was successful.
    /// - Throws: If the store cannot be destroyed.

    public func destroyPersistentStore(at storeURL: URL) throws {
        let psc = persistentContainer.persistentStoreCoordinator
        try psc.destroyPersistentStore(at: storeURL, ofType: NSSQLiteStoreType, options: nil)
    }

    /// Replace a persistent store.
    ///
    /// - Parameter destinationURL: An `NSURL` for the persistent store to be
    ///   replaced.
    /// - Parameter sourceURL: An `NSURL` for the source persistent store.
    /// - Returns: A flag indicating if the operation was successful.
    /// - Throws: If the persistent store cannot be replaced.

    public func replacePersistentStore(at url: URL, withPersistentStoreFrom sourceURL: URL) throws {
        let psc = persistentContainer.persistentStoreCoordinator
        try psc.replacePersistentStore(at: url, destinationOptions: nil,
            withPersistentStoreFrom: sourceURL, sourceOptions: nil, ofType: NSSQLiteStoreType)
    }

    /// Create and return a new private queue `NSManagedObjectContext`. The
    /// new context is set to consume `NSManagedObjectContextSave` broadcasts
    /// automatically.
    ///
    /// - Returns: A new private managed object context

    public func newPrivateContext() -> NSManagedObjectContext {
        return persistentContainer.newBackgroundContext()
    }

    /// Execute a block on a new private queue context.
    ///
    /// - Parameter block: A block to execute on a newly created private
    ///   context. The context is passed to the block as a parameter.

    public func performBackgroundTask(block: @escaping (NSManagedObjectContext) -> Void) {
        persistentContainer.performBackgroundTask(block)
    }

    /// Return an object ID for the specified URI representation if a matching
    /// store is available.
    ///
    /// - Parameter storeURL: An `NSURL` containing a URI of a managed object.
    /// - Returns: An optional `NSManagedObjectID`.

    public func managedObjectID(forURIRepresentation storeURL: URL) -> NSManagedObjectID? {
        let psc = persistentContainer.persistentStoreCoordinator
        return psc.managedObjectID(forURIRepresentation: storeURL)
    }

    private let persistentContainer: NSPersistentContainer;

    private func storeDescription(with url: URL) -> NSPersistentStoreDescription {
        let description = NSPersistentStoreDescription(url: url)
        description.shouldMigrateStoreAutomatically = shouldMigrateStoreAutomatically
        description.shouldInferMappingModelAutomatically = shouldInferMappingModelAutomatically
        description.shouldAddStoreAsynchronously = shouldAddStoreAsynchronously
        description.isReadOnly = isReadOnly
        return description
    }
}