Unleashing the real power of Core Data with the elegance and safety of Swift
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README.md

README.md

CoreStore

Version Platform License Carthage compatible

Unleashing the real power of Core Data with the elegance and safety of Swift

Click here for a wiki version of this README

What CoreStore does better:

  • Heavily supports multiple persistent stores per data stack, just the way .xcdatamodeld files are designed to. CoreStore will also manage one data stack by default, but you can create and manage as many as you need.
  • Incremental Migrations! Just tell the data stack the sequence of model versions and CoreStore will automatically use incremental migrations if needed on stores added to that stack.
  • Ability to plug-in your own logging framework
  • Gets around a limitation with other Core Data wrappers where the entity name should be the same as the NSManagedObject subclass name. CoreStore loads entity-to-class mappings from the managed object model file, so you are free to name them independently.
  • Provides type-safe, easy to configure observers to replace NSFetchedResultsController and KVO
  • Exposes API not just for fetching, but also for querying aggregates and property values
  • Makes it hard to fall into common concurrency mistakes. All NSManagedObjectContext tasks are encapsulated into safer, higher-level abstractions without sacrificing flexibility and customizability.
  • Exposes clean and convenient API designed around Swift’s code elegance and type safety.
  • Documentation! No magic here; all public classes, functions, properties, etc. have detailed Apple Docs. This README also introduces a lot of concepts and explains a lot of CoreStore's behavior.
  • New in 1.3.0: Efficient importing utilities!

CoreStore's goal is not to expose shorter, magical syntax, but to provide an API that focuses on readability, consistency, and safety.

Contents

TL;DR (a.k.a. sample codes)

Setting-up with incremental migration support:

CoreStore.defaultStack = DataStack(
    modelName: "MyStore",
    migrationChain: ["MyStore", "MyStoreV2", "MyStoreV3"]
)

Adding a store:

do {
    try CoreStore.addSQLiteStore(
        fileName: "MyStore.sqlite",
        completion: { (result) -> Void in
            // ...
        }
    )
}
catch {
    // ...
}

Starting transactions:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let person = transaction.create(Into(MyPersonEntity))
    person.name = "John Smith"
    person.age = 42

    transaction.commit { (result) -> Void in
        switch result {
            case .Success(let hasChanges): print("success!")
            case .Failure(let error): print(error)
        }
    }
}

Fetching objects:

let people = CoreStore.fetchAll(From(MyPersonEntity))
let people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where("age > 30"),
    OrderBy(.Ascending("name"), .Descending("age")),
    Tweak { (fetchRequest) -> Void in
        fetchRequest.includesPendingChanges = false
    }
)

Querying values:

let maxAge = CoreStore.queryValue(
    From(MyPersonEntity),
    Select<Int>(.Maximum("age"))
)

But really, there's a reason I wrote this huge README. Read up on the details!

Check out the CoreStoreDemo app project for sample codes as well!

Architecture

For maximum safety and performance, CoreStore will enforce coding patterns and practices it was designed for. (Don't worry, it's not as scary as it sounds.) But it is advisable to understand the "magic" of CoreStore before you use it in your apps.

If you are already familiar with the inner workings of CoreData, here is a mapping of CoreStore abstractions:

Core Data CoreStore
NSManagedObjectModel / NSPersistentStoreCoordinator
(.xcdatamodeld file)
DataStack
NSPersistentStore
("Configuration"s in the .xcdatamodeld file)
DataStack configuration
(multiple sqlite / in-memory stores per stack)
NSManagedObjectContext BaseDataTransaction subclasses
(SynchronousDataTransaction, AsynchronousDataTransaction, UnsafeDataTransaction)

Popular libraries RestKit and MagicalRecord set up their NSManagedObjectContexts this way:

nested contexts

Nesting context saves from child context to the root context ensures maximum data integrity between contexts without blocking the main queue. But as Florian Kugler's investigation found out, merging contexts is still by far faster than saving nested contexts. CoreStore's DataStack takes the best of both worlds by treating the main NSManagedObjectContext as a read-only context, and only allows changes to be made within transactions on the child context:

nested contexts and merge hybrid

This allows for a butter-smooth main thread, while still taking advantage of safe nested contexts.

Setting up

The simplest way to initialize CoreStore is to add a default store to the default stack:

do {
    try CoreStore.addSQLiteStoreAndWait()
}
catch {
    // ...
}

This one-liner does the following:

  • Triggers the lazy-initialization of CoreStore.defaultStack with a default DataStack
  • Sets up the stack's NSPersistentStoreCoordinator, the root saving NSManagedObjectContext, and the read-only main NSManagedObjectContext
  • Adds an SQLite store in the "Application Support" directory with the file name "[App bundle name].sqlite"
  • Creates and returns the NSPersistentStore instance on success, or an NSError on failure

For most cases, this configuration is usable as it is. But for more hardcore settings, refer to this extensive example:

let dataStack = DataStack(
    modelName: "MyModel", // loads from the "MyModel.xcdatamodeld" file
    migrationChain: ["MyStore", "MyStoreV2", "MyStoreV3"] // model versions for incremental migrations
)

do {
    // creates an in-memory store with entities from the "Config1" configuration in the .xcdatamodeld file
    let persistentStore = try dataStack.addInMemoryStoreAndWait(configuration: "Config1") // persistentStore is an NSPersistentStore instance
    print("Successfully created an in-memory store: \(persistentStore)"
}
catch {
    print("Failed creating an in-memory store with error: \(error as NSError)"
}

do {
    try dataStack.addSQLiteStore(
        fileURL: sqliteFileURL, // set the target file URL for the sqlite file
        configuration: "Config2", // use entities from the "Config2" configuration in the .xcdatamodeld file
        resetStoreOnModelMismatch: true,
        completion: { (result) -> Void in
            switch result {
            case .Success(let persistentStore):
                print("Successfully added sqlite store: \(persistentStore)"
            case .Failure(let error):
                print("Failed adding sqlite store with error: \(error)"
            }
        }
    )
}
catch {
    print("Failed adding sqlite store with error: \(error as NSError)"
}

CoreStore.defaultStack = dataStack // pass the dataStack to CoreStore for easier access later on

(If you have never heard of "Configurations", you'll find them in your .xcdatamodeld file) xcode configurations screenshot

In our sample code above, note that you don't need to do the CoreStore.defaultStack = dataStack line. You can just as well hold a reference to the DataStack like below and call all its instance methods directly:

class MyViewController: UIViewController {
    let dataStack = DataStack(modelName: "MyModel")
    override func viewDidLoad() {
        super.viewDidLoad()
        do {
            try self.dataStack.addSQLiteStoreAndWait()
        }
        catch { // ...
        }
    }
    func methodToBeCalledLaterOn() {
        let objects = self.dataStack.fetchAll(From(MyEntity))
        print(objects)
    }
}

The difference is when you set the stack as the CoreStore.defaultStack, you can call the stack's methods directly from CoreStore itself:

class MyViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        do {
            try CoreStore.addSQLiteStoreAndWait()
        }
        catch { // ...
        }
    }
    func methodToBeCalledLaterOn() {
        let objects = CoreStore.fetchAll(From(MyEntity))
        print(objects)
    }
}

Migrations

So far we have only seen addSQLiteStoreAndWait(...) used to initialize our persistent store. As the method name's "AndWait" suffix suggests, this method will block, even if a migration occurs. If migrations are expected, the asynchronous variant addSQLiteStore(... completion:) method is recommended:

do {
    let progress: NSProgress = try dataStack.addSQLiteStore(
        fileName: "MyStore.sqlite",
        configuration: "Config2",
        completion: { (result) -> Void in
            switch result {
            case .Success(let persistentStore):
                print("Successfully added sqlite store: \(persistentStore)"
            case .Failure(let error):
                print("Failed adding sqlite store with error: \(error)"
            }
        }
    )
}
catch {
    print("Failed adding sqlite store with error: \(error as NSError)"
}

The completion block reports a PersistentStoreResult that indicates success or failure.

addSQLiteStore(...) throws an error if the store at the specified URL conflicts with an existing store in the DataStack, or if an existing sqlite file could not be read. If an error is thrown, the completion block will not be executed.

Notice that this method also returns an optional NSProgress. If nil, no migrations are needed, thus progress reporting is unnecessary as well. If not nil, you can use this to track migration progress by using standard KVO on the "fractionCompleted" key, or by using a closure-based utility exposed in NSProgress+Convenience.swift:

progress?.setProgressHandler { [weak self] (progress) -> Void in
    self?.progressView?.setProgress(Float(progress.fractionCompleted), animated: true)
    self?.percentLabel?.text = progress.localizedDescription // "50% completed"
    self?.stepLabel?.text = progress.localizedAdditionalDescription // "0 of 2"
}

This closure is executed on the main thread so UIKit calls can be done safely.

Incremental migrations

By default, CoreStore uses Core Data's default automatic migration mechanism. In other words, CoreStore will try to migrate the existing persistent store to the .xcdatamodeld file's current model version. If no mapping model is found from the store's version to the data model's version, CoreStore gives up and reports an error.

The DataStack lets you specify hints on how to break a migration into several sub-migrations using a MigrationChain. This is typically passed to the DataStack initializer and will be applied to all stores added to the DataStack with addSQLiteStore(...) and its variants:

let dataStack = DataStack(migrationChain: 
    ["MyAppModel", "MyAppModelV2", "MyAppModelV3", "MyAppModelV4"])

The most common usage is to pass in the .xcdatamodeld version names in increasing order as above.

For more complex migration paths, you can also pass in a version tree that maps the key-values to the source-destination versions:

let dataStack = DataStack(migrationChain: [
    "MyAppModel": "MyAppModelV3",
    "MyAppModelV2": "MyAppModelV4",
    "MyAppModelV3": "MyAppModelV4"
])

This allows for different migration paths depending on the starting version. The example above resolves to the following paths:

  • MyAppModel-MyAppModelV3-MyAppModelV4
  • MyAppModelV2-MyAppModelV4
  • MyAppModelV3-MyAppModelV4

Initializing with empty values (either nil, [], or [:]) instructs the DataStack to disable incremental migrations and revert to the default migration behavior (i.e. use the .xcdatamodel's current version as the final version):

let dataStack = DataStack(migrationChain: nil)

The MigrationChain is validated when passed to the DataStack and unless it is empty, will raise an assertion if any of the following conditions are met:

  • a version appears twice in an array
  • a version appears twice as a key in a dictionary literal
  • a loop is found in any of the paths

One important thing to remember is that if a MigrationChain is specified, the .xcdatamodeld's "Current Version" will be bypassed and the MigrationChain's leafmost version will be the DataStack's base model version.

Forecasting migrations

Sometimes migrations are huge and you may want prior information so your app could display a loading screen, or to display a confirmation dialog to the user. For this, CoreStore provides a requiredMigrationsForSQLiteStore(...) method you can use to inspect a persistent store before you actually call addSQLiteStore(...):

do {
    let migrationTypes: [MigrationType] = CoreStore.requiredMigrationsForSQLiteStore(fileName: "MyStore.sqlite")
    if migrationTypes.count > 1
        || (migrationTypes.filter { $0.isHeavyweightMigration }.count) > 0 {
        // ... Show special waiting screen
    }
    else if migrationTypes.count > 0 {
        // ... Show simple activity indicator
    }
    else {
        // ... Do nothing
    }

    CoreStore.addSQLiteStore(/* ... */)
}
catch {
    // ...
}

requiredMigrationsForSQLiteStore(...) returns an array of MigrationTypes, where each item in the array may be either of the following values:

case Lightweight(sourceVersion: String, destinationVersion: String)
case Heavyweight(sourceVersion: String, destinationVersion: String)

Each MigrationType indicates the migration type for each step in the MigrationChain. Use these information as fit for your app.

Saving and processing transactions

To ensure deterministic state for objects in the read-only NSManagedObjectContext, CoreStore does not expose API's for updating and saving directly from the main context (or any other context for that matter.) Instead, you spawn transactions from DataStack instances:

let dataStack = self.dataStack
dataStack.beginAsynchronous { (transaction) -> Void in
    // make changes
    transaction.commit()
}

or for the default stack, directly from CoreStore:

CoreStore.beginAsynchronous { (transaction) -> Void in
    // make changes
    transaction.commit()
}

The commit() method saves the changes to the persistent store. If commit() is not called when the transaction block completes, all changes within the transaction is discarded.

The examples above use beginAsynchronous(...), but there are actually 3 types of transactions at your disposal: asynchronous, synchronous, and unsafe.

Transaction types

Asynchronous transactions

are spawned from beginAsynchronous(...). This method returns immediately and executes its closure from a background serial queue:

CoreStore.beginAsynchronous { (transaction) -> Void in
    // make changes
    transaction.commit()
}

Transactions created from beginAsynchronous(...) are instances of AsynchronousDataTransaction.

Synchronous transactions

are created from beginSynchronous(...). While the syntax is similar to its asynchronous counterpart, beginSynchronous(...) waits for its transaction block to complete before returning:

CoreStore.beginSynchronous { (transaction) -> Void in
    // make changes
    transaction.commit()
} 

transaction above is a SynchronousDataTransaction instance.

Since beginSynchronous(...) technically blocks two queues (the caller's queue and the transaction's background queue), it is considered less safe as it's more prone to deadlock. Take special care that the closure does not block on any other external queues.

Unsafe transactions

are special in that they do not enclose updates within a closure:

let transaction = CoreStore.beginUnsafe()
// make changes
downloadJSONWithCompletion({ (json) -> Void in

    // make other changes
    transaction.commit()
})
downloadAnotherJSONWithCompletion({ (json) -> Void in

    // make some other changes
    transaction.commit()
})

This allows for non-contiguous updates. Do note that this flexibility comes with a price: you are now responsible for managing concurrency for the transaction. As uncle Ben said, "with great power comes great race conditions."

As the above example also shows, only unsafe transactions are allowed to call commit() multiple times; doing so with synchronous and asynchronous transactions will trigger an assert.

You've seen how to create transactions, but we have yet to see how to make creates, updates, and deletes. The 3 types of transactions above are all subclasses of BaseDataTransaction, which implements the methods shown below.

Creating objects

The create(...) method accepts an Into clause which specifies the entity for the object you want to create:

let person = transaction.create(Into(MyPersonEntity))

While the syntax is straightforward, CoreStore does not just naively insert a new object. This single line does the following:

  • Checks that the entity type exists in any of the transaction's parent persistent store
  • If the entity belongs to only one persistent store, a new object is inserted into that store and returned from create(...)
  • If the entity does not belong to any store, an assert will be triggered. This is a programmer error and should never occur in production code.
  • If the entity belongs to multiple stores, an assert will be triggered. This is also a programmer error and should never occur in production code. Normally, with Core Data you can insert an object in this state but saving the NSManagedObjectContext will always fail. CoreStore checks this for you at creation time when it makes sense (not during save).

If the entity exists in multiple configurations, you need to provide the configuration name for the destination persistent store:

let person = transaction.create(Into<MyPersonEntity>("Config1"))

or if the persistent store is the auto-generated "Default" configuration, specify nil:

let person = transaction.create(Into<MyPersonEntity>(nil))

Note that if you do explicitly specify the configuration name, CoreStore will only try to insert the created object to that particular store and will fail if that store is not found; it will not fall back to any other configuration that the entity belongs to.

Updating objects

After creating an object from the transaction, you can simply update its properties as normal:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let person = transaction.create(Into(MyPersonEntity))
    person.name = "John Smith"
    person.age = 30
    transaction.commit()
}

To update an existing object, fetch the object's instance from the transaction:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let person = transaction.fetchOne(
        From(MyPersonEntity),
        Where("name", isEqualTo: "Jane Smith")
    )
    person.age = person.age + 1
    transaction.commit()
}

(For more about fetching, see Fetching and querying)

Do not update an instance that was not created/fetched from the transaction. If you have a reference to the object already, use the transaction's edit(...) method to get an editable proxy instance for that object:

let jane: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    // WRONG: jane.age = jane.age + 1
    // RIGHT:
    let jane = transaction.edit(jane)! // using the same variable name protects us from misusing the non-transaction instance
    jane.age = jane.age + 1
    transaction.commit()
}

This is also true when updating an object's relationships. Make sure that the object assigned to the relationship is also created/fetched from the transaction:

let jane: MyPersonEntity = // ...
let john: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    // WRONG: jane.friends = [john]
    // RIGHT:
    let jane = transaction.edit(jane)!
    let john = transaction.edit(john)!
    jane.friends = NSSet(array: [john])
    transaction.commit()
}

Deleting objects

Deleting an object is simpler because you can tell a transaction to delete an object directly without fetching an editable proxy (CoreStore does that for you):

let john: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    transaction.delete(john)
    transaction.commit()
}

or several objects at once:

let john: MyPersonEntity = // ...
let jane: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    transaction.delete(john, jane)
    // transaction.delete([john, jane]) is also allowed
    transaction.commit()
}

If you do not have references yet to the objects to be deleted, transactions have a deleteAll(...) method you can pass a query to:

CoreStore.beginAsynchronous { (transaction) -> Void in
    transaction.deleteAll(
        From(MyPersonEntity)
        Where("age > 30")
    )
    transaction.commit()
}

Passing objects safely

Always remember that the DataStack and individual transactions manage different NSManagedObjectContexts so you cannot just use objects between them. That's why transactions have an edit(...) method:

let jane: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jane = transaction.edit(jane)!
    jane.age = jane.age + 1
    transaction.commit()
}

But CoreStore, DataStack and BaseDataTransaction have a very flexible fetchExisting(...) method that you can pass instances back and forth with:

let jane: MyPersonEntity = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jane = transaction.fetchExisting(jane)! // instance for transaction
    jane.age = jane.age + 1
    transaction.commit {
        let jane = CoreStore.fetchExisting(jane)! // instance for DataStack
        print(jane.age)
    }
}

fetchExisting(...) also works with multiple NSManagedObjects or with NSManagedObjectIDs:

var peopleIDs: [NSManagedObjectID] = // ...

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jane = transaction.fetchOne(
        From(MyPersonEntity),
        Where("name", isEqualTo: "Jane Smith")
    )
    jane.friends = NSSet(array: transactin.fetchExisting(peopleIDs)!)
    // ...
}

Importing data

Some times, if not most of the time, the data that we save to Core Data comes from external sources such as web servers or external files. Say you have a JSON dictionary, you may be extracting values as such:

let json: [String: AnyObject] = // ...
person.name = json["name"] as? NSString
person.age = json["age"] as? NSNumber
// ...

If you have many attributes, you don't want to keep repeating this mapping everytime you want to import data. CoreStore lets you write the data mapping code just once, and all you have to do is call importObject(...) or importUniqueObject(...) through BaseDataTransaction subclasses:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let json: [String: AnyObject] = // ...
    try! transaction.importObject(
        Into(MyPersonEntity),
        source: json
    )
    transaction.commit()
}

To support data import for an entity, implement either ImportableObject or ImportableUniqueObject on the NSManagedObject subclass:

  • ImportableObject: Use this protocol if the object have no inherent uniqueness and new objects should always be added when calling importObject(...).
  • ImportableUniqueObject: Use this protocol to specify a unique ID for an object that will be used to distinguish whether a new object should be created or if an existing object should be updated when calling importUniqueObject(...).

Both protocols require implementers to specify an ImportSource which can be set to any type that the object can extract data from:

typealias ImportSource = NSDictionary
typealias ImportSource = [String: AnyObject]
typealias ImportSource = NSData

You can even use external types from popular 3rd-party JSON libraries (SwiftyJSON's JSON type is a personal favorite), or just simple tuples or primitives.

ImportableObject

ImportableObject is a very simple protocol:

public protocol ImportableObject: class {
    typealias ImportSource
    static func shouldInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) -> Bool
    func didInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws
}

First, set ImportSource to the expected type of the data source:

typealias ImportSource = [String: AnyObject]

This lets us call importObject(_:source:) with any [String: AnyObject] type as the argument to source:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let json: [String: AnyObject] = // ...
    try! transaction.importObject(
        Into(MyPersonEntity),
        source: json
    )
    // ...
}

The actual extraction and assignment of values should be implemented in the didInsertFromImportSource(...) method of the ImportableObject protocol:

func didInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws {
    self.name = source["name"] as? NSString
    self.age = source["age"] as? NSNumber
    // ...
}

Transactions also let you import multiple objects at once using the importObjects(_:sourceArray:) method:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jsonArray: [[String: AnyObject]] = // ...
    try! transaction.importObjects(
        Into(MyPersonEntity),
        sourceArray: jsonArray
    )
    // ...
}

Doing so tells the transaction to iterate through the array of import sources and calls shouldInsertFromImportSource(...) on the ImportableObject to determine which instances should be created. You can do validations and return false from shouldInsertFromImportSource(...) if you want to skip importing from a source and continue on with the other sources in the array.

If on the other hand, your validation in one of the sources failed in such a manner that all other sources should also be cancelled, you can throw from within didInsertFromImportSource(...):

func didInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws {
    self.name = source["name"] as? NSString
    self.age = source["age"] as? NSNumber
    // ...
    if self.name == nil {
        throw Errors.InvalidNameError
    }
}

Doing so can let you abandon an invalid transaction immediately:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jsonArray: [[String: AnyObject]] = // ...
    do {
        try transaction.importObjects(
            Into(MyPersonEntity),
            sourceArray: jsonArray
        )
    }
    catch {
        return // Woops, don't save
    }
    transaction.commit {
        // ...
    }
}

ImportableUniqueObject

Typically, we don't just keep creating objects every time we import data. Usually we also need to update already existing objects. Implementing the ImportableUniqueObject protocol lets you specify a "unique ID" that transactions can use to search existing objects before creating new ones:

public protocol ImportableUniqueObject: ImportableObject {
    typealias ImportSource
    typealias UniqueIDType: NSObject

    static var uniqueIDKeyPath: String { get }
    var uniqueIDValue: UniqueIDType { get set }

    static func shouldInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) -> Bool
    static func shouldUpdateFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) -> Bool
    static func uniqueIDFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws -> UniqueIDType?
    func didInsertFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws
    func updateFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws
}

Notice that it has the same insert methods as ImportableObject, with additional methods for updates and for specifying the unique ID:

class var uniqueIDKeyPath: String {
    return "personID" 
}
var uniqueIDValue: NSNumber { 
    get { return self.personID }
    set { self.personID = newValue }
}
class func uniqueIDFromImportSource(source: ImportSource, inTransaction transaction: BaseDataTransaction) throws -> NSNumber? {
    return source["id"] as? NSNumber
}

For ImportableUniqueObject, the extraction and assignment of values should be implemented from the updateFromImportSource(...) method. The didInsertFromImportSource(...) by default calls updateFromImportSource(...), but you can separate the implementation for inserts and updates if needed.

You can then call create/update an object by calling a transaction's importUniqueObject(...) method:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let json: [String: AnyObject] = // ...
    try! transaction.importUniqueObject(
        Into(MyPersonEntity),
        source: json
    )
    // ...
}

or multiple objects at once with the importUniqueObjects(...) method:

CoreStore.beginAsynchronous { (transaction) -> Void in
    let jsonArray: [[String: AnyObject]] = // ...
    try! transaction.importObjects(
        Into(MyPersonEntity),
        sourceArray: jsonArray
    )
    // ...
}

As with ImportableObject, you can control wether to skip importing an object by implementing shouldInsertFromImportSource(...) and shouldUpdateFromImportSource(...), or to cancel all objects by throwing an error from the uniqueIDFromImportSource(...), didInsertFromImportSource(...) or updateFromImportSource(...) methods.

Fetching and Querying

Before we dive in, be aware that CoreStore distinguishes between fetching and querying:

  • A fetch executes searches from a specific transaction or data stack. This means fetches can include pending objects (i.e. before a transaction calls on commit().) Use fetches when:
    • results need to be NSManagedObject instances
    • unsaved objects should be included in the search (though fetches can be configured to exclude unsaved ones)
  • A query pulls data straight from the persistent store. This means faster searches when computing aggregates such as count, min, max, etc. Use queries when:
    • you need to compute aggregate functions (see below for a list of supported functions)
    • results can be raw values like NSStrings, NSNumbers, Ints, NSDates, an NSDictionary of key-values, etc.
    • only values for specified attribute keys need to be included in the results
    • unsaved objects should be ignored

From clause

The search conditions for fetches and queries are specified using clauses. All fetches and queries require a From clause that indicates the target entity type:

let people = CoreStore.fetchAll(From(MyPersonEntity))
// CoreStore.fetchAll(From<MyPersonEntity>()) works as well

people in the example above will be of type [MyPersonEntity]. The From(MyPersonEntity) clause indicates a fetch to all persistent stores that MyPersonEntity belong to.

If the entity exists in multiple configurations and you need to only search from a particular configuration, indicate in the From clause the configuration name for the destination persistent store:

let people = CoreStore.fetchAll(From<MyPersonEntity>("Config1")) // ignore objects in persistent stores other than the "Config1" configuration

or if the persistent store is the auto-generated "Default" configuration, specify nil:

let person = CoreStore.fetchAll(From<MyPersonEntity>(nil))

Now we know how to use a From clause, let's move on to fetching and querying.

Fetching

There are currently 5 fetch methods you can call from CoreStore, from a DataStack instance, or from a BaseDataTransaction instance. All of the methods below accept the same parameters: a required From clause, and an optional series of Where, OrderBy, and/or Tweak clauses.

  • fetchAll(...) - returns an array of all objects that match the criteria.
  • fetchOne(...) - returns the first object that match the criteria.
  • fetchCount(...) - returns the number of objects that match the criteria.
  • fetchObjectIDs(...) - returns an array of NSManagedObjectIDs for all objects that match the criteria.
  • fetchObjectID(...) - returns the NSManagedObjectIDs for the first objects that match the criteria.

Each method's purpose is straightforward, but we need to understand how to set the clauses for the fetch.

Where clause

The Where clause is CoreStore's NSPredicate wrapper. It specifies the search filter to use when fetching (or querying). It implements all initializers that NSPredicate does (except for -predicateWithBlock:, which Core Data does not support):

var people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where("%K > %d", "age", 30) // string format initializer
)
people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where(true) // boolean initializer
)

If you do have an existing NSPredicate instance already, you can pass that to Where as well:

let predicate = NSPredicate(...)
var people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where(predicate) // predicate initializer
)

Where clauses also implement the &&, ||, and ! logic operators, so you can provide logical conditions without writing too much AND, OR, and NOT strings:

var people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where("age > %d", 30) && Where("gender == %@", "M")
)

If you do not provide a Where clause, all objects that belong to the specified From will be returned.

OrderBy clause

The OrderBy clause is CoreStore's NSSortDescriptor wrapper. Use it to specify attribute keys in which to sort the fetch (or query) results with.

var mostValuablePeople = CoreStore.fetchAll(
    From(MyPersonEntity),
    OrderBy(.Descending("rating"), .Ascending("surname"))
)

As seen above, OrderBy accepts a list of SortKey enumeration values, which can be either .Ascending or .Descending.

You can use the + and += operator to append OrderBys together. This is useful when sorting conditionally:

var orderBy = OrderBy(.Descending("rating"))
if sortFromYoungest {
    orderBy += OrderBy(.Ascending("age"))
}
var mostValuablePeople = CoreStore.fetchAll(
    From(MyPersonEntity),
    orderBy
)

Tweak clause

The Tweak clause lets you, uh, tweak the fetch (or query). Tweak exposes the NSFetchRequest in a closure where you can make changes to its properties:

var people = CoreStore.fetchAll(
    From(MyPersonEntity),
    Where("age > %d", 30),
    OrderBy(.Ascending("surname")),
    Tweak { (fetchRequest) -> Void in
        fetchRequest.includesPendingChanges = false
        fetchRequest.returnsObjectsAsFaults = false
        fetchRequest.includesSubentities = false
    }
)

The clauses are evaluated the order they appear in the fetch/query, so you typically need to set Tweak as the last clause. Tweak's closure is executed only just before the fetch occurs, so make sure that any values captured by the closure is not prone to race conditions.

While Tweak lets you micro-configure the NSFetchRequest, note that CoreStore already preconfigured that NSFetchRequest to suitable defaults. Only use Tweak when you know what you are doing!

Querying

One of the functionalities overlooked by other Core Data wrapper libraries is raw properties fetching. If you are familiar with NSDictionaryResultType and -[NSFetchedRequest propertiesToFetch], you probably know how painful it is to setup a query for raw values and aggregate values. CoreStore makes this easy by exposing the 2 methods below:

  • queryValue(...) - returns a single raw value for an attribute or for an aggregate value. If there are multiple results, queryValue(...) only returns the first item.
  • queryAttributes(...) - returns an array of dictionaries containing attribute keys with their corresponding values.

Both methods above accept the same parameters: a required From clause, a required Select<T> clause, and an optional series of Where, OrderBy, GroupBy, and/or Tweak clauses.

Setting up the From, Where, OrderBy, and Tweak clauses is similar to how you would when fetching. For querying, you also need to know how to use the Select<T> and GroupBy clauses.

Select<T> clause

The Select<T> clause specifies the target attribute/aggregate key, as well as the expected return type:

let johnsAge = CoreStore.queryValue(
    From(MyPersonEntity),
    Select<Int>("age"),
    Where("name == %@", "John Smith")
)

The example above queries the "age" property for the first object that matches the Where condition. johnsAge will be bound to type Int?, as indicated by the Select<Int> generic type. For queryValue(...), the following are allowed as the return type (and therefore as the generic type for Select<T>):

  • Bool
  • Int8
  • Int16
  • Int32
  • Int64
  • Double
  • Float
  • String
  • NSNumber
  • NSString
  • NSDecimalNumber
  • NSDate
  • NSData
  • NSManagedObjectID
  • NSString

For queryAttributes(...), only NSDictionary is valid for Select, thus you are allowed to omit the generic type:

let allAges = CoreStore.queryAttributes(
    From(MyPersonEntity),
    Select("age")
)

If you only need a value for a particular attribute, you can just specify the key name (like we did with Select<Int>("age")), but several aggregate functions can also be used as parameter to Select:

  • .Average(...)
  • .Count(...)
  • .Maximum(...)
  • .Minimum(...)
  • .Sum(...)
let oldestAge = CoreStore.queryValue(
    From(MyPersonEntity),
    Select<Int>(.Maximum("age"))
)

For queryAttributes(...) which returns an array of dictionaries, you can specify multiple attributes/aggregates to Select:

let personJSON = CoreStore.queryAttributes(
    From(MyPersonEntity),
    Select("name", "age")
)

personJSON will then have the value:

[
    [
        "name": "John Smith",
        "age": 30
    ],
    [
        "name": "Jane Doe",
        "age": 22
    ]
]

You can also include an aggregate as well:

let personJSON = CoreStore.queryAttributes(
    From(MyPersonEntity),
    Select("name", .Count("friends"))
)

which returns:

[
    [
        "name": "John Smith",
        "count(friends)": 42
    ],
    [
        "name": "Jane Doe",
        "count(friends)": 231
    ]
]

The "count(friends)" key name was automatically used by CoreStore, but you can specify your own key alias if you need:

let personJSON = CoreStore.queryAttributes(
    From(MyPersonEntity),
    Select("name", .Count("friends", As: "friendsCount"))
)

which now returns:

[
    [
        "name": "John Smith",
        "friendsCount": 42
    ],
    [
        "name": "Jane Doe",
        "friendsCount": 231
    ]
]

GroupBy clause

The GroupBy clause lets you group results by a specified attribute/aggregate. This is useful only for queryAttributes(...) since queryValue(...) just returns the first value.

let personJSON = CoreStore.queryAttributes(
    From(MyPersonEntity),
    Select("age", .Count("age", As: "count")),
    GroupBy("age")
)

this returns dictionaries that shows the count for each "age":

[
    [
        "age": 42,
        "count": 1
    ],
    [
        "age": 22,
        "count": 1
    ]
]

Logging and error handling

One unfortunate thing when using some third-party libraries is that they usually pollute the console with their own logging mechanisms. CoreStore provides its own default logging class, but you can plug-in your own favorite logger by implementing the CoreStoreLogger protocol.

final class MyLogger: CoreStoreLogger {
    func log(#level: LogLevel, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
        // pass to your logger
    }
    
    func handleError(#error: NSError, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
        // pass to your logger
    }
    
    func assert(@autoclosure condition: () -> Bool, message: String, fileName: StaticString, lineNumber: Int, functionName: StaticString) {
        // pass to your logger
    }
}

Then pass an instance of this class to CoreStore:

CoreStore.logger = MyLogger()

Doing so channels all logging calls to your logger.

Note that to keep the call stack information intact, all calls to these methods are NOT thread-managed. Therefore you have to make sure that your logger is thread-safe or you may otherwise have to dispatch your logging implementation to a serial queue.

Observing changes and notifications

CoreStore provides type-safe wrappers for observing managed objects:

  • ObjectMonitor: use to monitor changes to a single NSManagedObject instance (instead of Key-Value Observing)
  • ListMonitor: use to monitor changes to a list of NSManagedObject instances (instead of NSFetchedResultsController)

Observe a single object

To observe an object, implement the ObjectObserver protocol and specify the EntityType:

class MyViewController: UIViewController, ObjectObserver {
    func objectMonitor(monitor: ObjectMonitor<MyPersonEntity>, willUpdateObject object: MyPersonEntity) {
        // ...
    }
    
    func objectMonitor(monitor: ObjectMonitor<MyPersonEntity>, didUpdateObject object: MyPersonEntity, changedPersistentKeys: Set<KeyPath>) {
        // ...
    }
    
    func objectMonitor(monitor: ObjectMonitor<MyPersonEntity>, didDeleteObject object: MyPersonEntity) {
        // ...
    }
}

We then need to keep a ObjectMonitor instance and register our ObjectObserver as an observer:

let person: MyPersonEntity = // ...
self.monitor = CoreStore.monitorObject(person)
self.monitor.addObserver(self)

The controller will then notify our observer whenever the object's attributes change. You can add multiple ObjectObservers to a single ObjectMonitor without any problem. This means you can just share around the ObjectMonitor instance to different screens without problem.

You can get ObjectMonitor's object through its object property. If the object is deleted, the object property will become nil to prevent further access.

While ObjectMonitor exposes removeObserver(...) as well, it only stores weak references of the observers and will safely unregister deallocated observers.

Observe a list of objects

To observe a list of objects, implement one of the ListObserver protocols and specify the EntityType:

class MyViewController: UIViewController, ListObserver {
    func listMonitorWillChange(monitor: ListMonitor<MyPersonEntity>) {
        // ...
    }
    
    func listMonitorDidChange(monitor: ListMonitor<MyPersonEntity>) {
        // ...
    }
}

Including ListObserver, there are 3 observer protocols you can implement depending on how detailed you need to handle a change notification:

  • ListObserver: lets you handle these callback methods:
    func listMonitorWillChange(monitor: ListMonitor<MyPersonEntity>)

    func listMonitorDidChange(monitor: ListMonitor<MyPersonEntity>)
  • ListObjectObserver: in addition to ListObserver methods, also lets you handle object inserts, updates, and deletes:
    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didInsertObject object: MyPersonEntity, toIndexPath indexPath: NSIndexPath)

    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didDeleteObject object: MyPersonEntity, fromIndexPath indexPath: NSIndexPath)

    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didUpdateObject object: MyPersonEntity, atIndexPath indexPath: NSIndexPath)

    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didMoveObject object: MyPersonEntity, fromIndexPath: NSIndexPath, toIndexPath: NSIndexPath)
  • ListSectionObserver: in addition to ListObjectObserver methods, also lets you handle section inserts and deletes:
    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didInsertSection sectionInfo: NSFetchedResultsSectionInfo, toSectionIndex sectionIndex: Int)

    func listMonitor(monitor: ListMonitor<MyPersonEntity>, didDeleteSection sectionInfo: NSFetchedResultsSectionInfo, fromSectionIndex sectionIndex: Int)

We then need to create a ListMonitor instance and register our ListObserver as an observer:

self.monitor = CoreStore.monitorList(
    From(MyPersonEntity),
    Where("age > 30"),
    OrderBy(.Ascending("name")),
    Tweak { (fetchRequest) -> Void in
        fetchRequest.fetchBatchSize = 20
    }
)
self.monitor.addObserver(self)

Similar to ObjectMonitor, a ListMonitor can also have multiple ListObservers registered to a single ListMonitor.

If you have noticed, the monitorList(...) method accepts Where, OrderBy, and Tweak clauses exactly like a fetch. As the list maintained by ListMonitor needs to have a deterministic order, at least the From and OrderBy clauses are required.

A ListMonitor created from monitorList(...) will maintain a single-section list. You can therefore access its contents with just an index:

let firstPerson = self.monitor[0]

If the list needs to be grouped into sections, create the ListMonitor instance with the monitorSectionedList(...) method and a SectionBy clause:

self.monitor = CoreStore.monitorSectionedList(
    From(MyPersonEntity),
    SectionBy("age"),
    Where("gender", isEqualTo: "M"),
    OrderBy(.Ascending("age"), .Ascending("name")),
    Tweak { (fetchRequest) -> Void in
        fetchRequest.fetchBatchSize = 20
    }
)

A list controller created this way will group the objects by the attribute key indicated by the SectionBy clause. One more thing to remember is that the OrderBy clause should sort the list in such a way that the SectionBy attribute would be sorted together (a requirement shared by NSFetchedResultsController.)

The SectionBy clause can also be passed a closure to transform the section name into a displayable string:

self.monitor = CoreStore.monitorSectionedList(
    From(MyPersonEntity),
    SectionBy("age") { (sectionName) -> String? in
        "\(sectionName) years old"
    },
    OrderBy(.Ascending("age"), .Ascending("name"))
)

This is useful when implementing a UITableViewDelegate's section header:

func tableView(tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
    let sectionInfo = self.monitor.sectionInfoAtIndex(section)
    // sectionInfo is an NSFetchedResultsSectionInfo instance
    return sectionInfo.name
}

To access the objects of a sectioned list, use an NSIndexPath or a tuple:

let indexPath = NSIndexPath(forRow: 2, inSection: 1)
let person1 = self.monitor[indexPath]
let person2 = self.monitor[1, 2]
// person1 and person2 are the same object

Roadmap

  • Data importing utilities for transactions
  • Support iCloud stores

Installation

  • Requires:
    • iOS 8 SDK and above
    • Swift 2.0 (XCode 7 beta 6)
  • Dependencies:

Install with Cocoapods

pod 'CoreStore'

This installs CoreStore as a framework. Declare import CoreStore in your swift file to use the library.

Install with Carthage

github "JohnEstropia/CoreStore" >= 1.3.0

Install as Git Submodule

git submodule add https://github.com/JohnEstropia/CoreStore.git <destination directory>

Drag and drop CoreStore.xcodeproj to your project.

To install as a framework:

Drag and drop CoreStore.xcodeproj to your project.

To include directly in your app module:

Add all .swift files to your project.

Changesets

Upgrading from v0.2.0 to 1.0.0

  • Renamed some classes/protocols to shorter, more relevant, easier to remember names:
  • ManagedObjectController to ObjectMonitor
  • ManagedObjectObserver to ObjectObserver
  • ManagedObjectListController to ListMonitor
  • ManagedObjectListChangeObserver to ListObserver
  • ManagedObjectListObjectObserver to ListObjectObserver
  • ManagedObjectListSectionObserver to ListSectionObserver
  • SectionedBy to SectionBy (match tense with OrderBy and GroupBy) The protocols above had their methods renamed as well, to retain the natural language semantics.
  • Several methods now throw errors insted of returning a result enum.
  • New migration utilities! (README still pending) Check out DataStack+Migration.swift and CoreStore+Migration.swift for the new methods, as well as DataStack.swift for its new initializer.

Contributions

While CoreStore's design is pretty solid and the unit test and demo app work well, CoreStore is pretty much still in its early stage. With more exposure to production code usage and criticisms from the developer community, CoreStore hopes to mature as well. Please feel free to report any issues, suggestions, or criticisms! 日本語で連絡していただいても構いません!

License

CoreStore is released under an MIT license. See the LICENSE file for more information