NEW: Subscribe to Hacking with Swift+ and accelerate your learning! >>

How to filter Core Data fetch requests using a predicate

Paul Hudson    @twostraws   

Updated for Xcode 12.0

Core Data fetch requests can use predicates in SwiftUI just like they can with UIKit, all by providing a predicate property to your @FetchRequest property wrapper.

If you followed my Core Data and SwiftUI set up instructions, you’ve already injected your managed object context into the SwiftUI environment.

Once that’s done, you can create a fetch request for one of your entities, passing in one or more sort descriptors and a predicate. These predicates are the same instances of NSPredicate that you would use without SwiftUI, which means you can use the same variety of string operations you would normally use.

For example, using the example data from my setup instructions we could create a predicate like this:

NSPredicate(format: "name == %@", "Python")

That will show details about Python, while ignoring other data.

We could use that inside a fetch request like this:

@FetchRequest(
    entity: ProgrammingLanguage.entity(),
    sortDescriptors: [
        NSSortDescriptor(keyPath: \ProgrammingLanguage.name, ascending: true),
    ],
    predicate: NSPredicate(format: "name == %@", "Python")
) var languages: FetchedResults<ProgrammingLanguage>

Because @FetchRequest uses standard Core Data predicates, you can create compound predicates too.

Hacking with Swift is sponsored by NSSpain

SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!

Find out more

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

Similar solutions…

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: 4.3/5

Link copied to your pasteboard.