NEW: Get your ticket to Hacking with Swift Live! >>

Conditional saving of NSManagedObjectContext

Paul Hudson    @twostraws   

We’ve been using the save() method of NSManagedObjectContext to flush out all unsaved changes to permanent storage, but what we haven’t done is check whether any changes actually need to saved. This is often OK, because it’s common to place save() calls only after we specifically made a change such as inserting or deleting data.

However, it’s also common to bulk your saves together so that you save everything at once, which has a lower performance impact. In fact, Apple specifically states that we should always check for uncommitted changes before calling save(), to avoid making Core Data do work that isn’t required.

Fortunately, we can check for changes in two ways. First, every managed object is given a hasChanges property, that is true when the object has unsaved changes. And, the entire context also contains a hasChanges property that checks whether any object owned by the context has changes.

So, rather than call save() directly you should always wrap it in a check first, like this:

if self.moc.hasChanges {
    try? self.moc.save()
}

It’s a small change to make, but it matters – there’s no point doing work that isn’t needed, no matter how small, particularly because if you do enough small work you realize you’ve stacked up some big work.

Hacking with Swift is sponsored by Essential Developer

SPONSORED From August 2nd to 8th you can join a FREE crash course for mid/senior iOS devs who want to achieve an expert level of technical and practical skills – it’s the fast track to being a complete senior developer!

Save your spot now

Sponsor Hacking with Swift and reach the world's largest Swift community!

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.7/5

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.