Core Data Cheat Sheet for Swift iOS Developers

Wed, 18 Feb 2015 18:20:59 +0000

Updated on July 27, 2016 – Additional Cheats

Having trouble recalling how to perform basic Core Data operations? This cheat sheet is a handy reference to keep you productive with Core Data and Swift!

The code snippets below are here to help jog your memory when it’s been a while since you’ve worked in Core Data. They could also be helpful for newcomers to iOS development, Core Data, and Swift.

One assumption I’m making in this post is that you’ve created NSManagedObject subclasses for your entities to make them easier to work with in a type-safe way. If you need help getting started with that, I’ve written a walk-through to guide you through that process.

Querying

Fetch all entities

// Assuming type has a reference to managed object context

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    // Do something with fetchedEntities
} catch {
    // Do something in response to error condition
}

Fetch maximum of N entities

// Assuming type has a reference to managed object context

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
fetchRequest.fetchLimit = 10
do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    // Do something with fetchedEntities
} catch {
    // Do something in response to error condition
}

Insert a new entity

// Assuming encapsulating Type has a reference to managed object context

let newEntity = NSEntityDescription.insertNewObjectForEntityForName("MyEntity", inManagedObjectContext: self.managedObjectContext) as! MyEntity
// Set properties

do {
    try self.managedObjectContext.save()
} catch {
    // Do something in response to error condition
}

Update a single entity

// Assuming type has a reference to managed object context

// Assuming that a specific NSManagedObject's objectID property is accessible
// Alternatively, could supply a predicate expression that's precise enough
// to select only a _single_ entity
let predicate = NSPredicate(format: "objectID == %@", objectIDFromNSManagedObject)

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
fetchRequest.predicate = predicate

do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    fetchedEntities.first?.FirstPropertyToUpdate = NewValue
    fetchedEntities.first?.SecondPropertyToUpdate = NewValue
    // ... Update additional properties with new values
} catch {
    // Do something in response to error condition
}

do {
    try self.managedObjectContext.save()
} catch {
    // Do something in response to error condition
}

Update multiple-entities

// Assuming type has a reference to managed object context

let predicate = NSPredicate(format: "MyEntityAttribute == %@", "Matching Value")

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
fetchRequest.predicate = predicate

do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    
    for entity in fetchedEntities {
        entity.FirstPropertyToUpdate = NewValue
        entity.SecondPropertyToUpdate = NewValue
        // ... Update additional properties with new values
    }
} catch {
    // Do something in response to error condition
}

do {
    try self.managedObjectContext.save()
} catch {
    // Do something in response to error condition
}

Delete a single entity

// Assuming type has a reference to managed object context

// Assuming that a specific NSManagedObject's objectID property is accessible
// Alternatively, could supply a predicate expression that's precise enough
// to select only a _single_ entity
let predicate = NSPredicate(format: "objectID == %@", objectIDFromNSManagedObject)

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
fetchRequest.predicate = predicate

do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    if let entityToDelete = fetchedEntities.first {
        self.managedObjectContext.deleteObject(entityToDelete)
    }
} catch {
    // Do something in response to error condition
}

do {
    try self.managedObjectContext.save()
} catch {
    // Do something in response to error condition
}

Delete multiple-entities

// Assuming type has a reference to managed object context

let predicate = NSPredicate(format: "MyEntityAttribute == %@", "Matching Value")

let fetchRequest = NSFetchRequest(entityName: "MyEntity")
fetchRequest.predicate = predicate

do {
    let fetchedEntities = try self.managedObjectContext.executeFetchRequest(fetchRequest) as! [MyEntity]
    
    for entity in fetchedEntities {
        self.managedObjectContext.deleteObject(entity)
    }
} catch {
    // Do something in response to error condition
}

do {
    try self.managedObjectContext.save()
} catch {
    // Do something in response to error condition
}

Migrate Core Data Model with Automatic Migrations

let model = // set up model

let pscOptions = [NSMigratePersistentStoresAutomaticallyOption : true, NSInferMappingModelAutomaticallyOption : true]
    
let psc = NSPersistentStoreCoordinator(managedObjectModel: model)
try! psc.addPersistentStore(ofType: NSSQLiteStoreType, configurationName: nil, at: storeURL, options: pscOptions)

Swift UITableViewDataSource Cheat Sheet

Mon, 24 Nov 2014 22:04:28 +0000

iOS developers will quickly recognize that there are a set of methods that always tend to get implemented when dealing with UITableViews . The problem I consistently face is remembering that set of methods that belong to the UITableViewDataSource (and UITableViewDelegate ) protocols. I find myself option-clicking the protocol name to remember the method signatures I need, since Xcode doesn’t have a way to stub out the methods involved with a protocol (C# developers working in Visual Studio like myself are spoiled!).

I’m sure cheat sheets like this already exist, but I thought, “Why not have one that I can reference from my own blog?”… In fact, I’ve gone ahead and turned the code below into a snippet in Xcode, but just in case I ever lose that, I’ve got this post, which stubs out dummy implementations of the three most common UITableViewDataSource protocol methods.

I’d be delighted if it helped my readers as well, so without further ado, here’s my UITableViewDataSource cheat sheet, which should allow you (and me) to copy and paste directly into our UITableViewDataSource class for a quick start:

 1func numberOfSectionsInTableView(tableView: UITableView) -> Int {
 2    return 1 // This was put in mainly for my own unit testing
 3}
 4
 5func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
 6    return dataSourceArray.count // Most of the time my data source is an array of something...  will replace with the actual name of the data source
 7}
 8
 9func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
10    // Note:  Be sure to replace the argument to dequeueReusableCellWithIdentifier with the actual identifier string!
11    let cell = tableView.dequeueReusableCellWithIdentifier("ReplaceWithCellIdentifier") as! UITableViewCell
12    
13    // set cell's textLabel.text property
14    // set cell's detailTextLabel.text property
15    return cell
16}

Cheat Sheet on Andrew Bancroft