SwiftData’s new Index and Unique macros

Introduction

These are notes taken during the WWDC24 session: What’s new in SwiftData.

Alongside the existing Attribute, Relationship, and Transient macros, new Index and Unique macros are now available in SwiftData starting with iOS 18.

Index

The Index macro specifies model properties that are frequently filtered and sorted to enhance the efficiency of these operations.

In my app, Huh? Dictionary, when users search for a word in the search bar, previously searched entries appear below it, sorted by recency and filtered by relevance. Therefore, the word property of SearchEntry is an ideal candidate for the Index macro.

import Foundation
import SwiftData

@Model
final class SearchEntry {
    
    // MARK: - Macros
    
    #Index<SearchEntry>([\.word])
    
    // MARK: - Init
    
    init(word: String) {
        self.word = word
    }
    
    // MARK: - Properties
    
    @Attribute(.unique) var word: String
    var date: Date = Date.now
    
}

Similar to the Unique macro below, properties can be grouped together in an array. This is useful when filtering or sorting requires them in the same boolean expression. For example, if users can enter a date range before submitting a search query, the indices for my Index macro would differ to optimize efficiency.

#Index<SearchEntry>([\.word], [\.word, \.date])

Unique

The Unique macro extends the Attribute’s unique Option by ensuring a model entity is unique based on combinations of multiple properties. For instance, if a Person entity has id, givenName, and familyName, uniqueness can be defined based on id alone or givenName and familyName together.

import Foundation
import SwiftData

@Model
final class Person {
    
    // MARK: - Macros
    
    #Unique<Person>([\.id], [\.givenName, \.familyName])
    
    // MARK: - Init
    
    init(id: UUID, givenName: String, familyName: String) {
        self.id = id
        self.givenName = givenName
        self.familyName = familyName
    }
    
    // MARK: - Properties
    
    var id: UUID
    var givenName: String
    var familyName: String
    
}

Conclusion

The Index and Unique macros introduce significant improvements to SwiftData, enhancing efficiency, storage, and speed. Despite being only a year old, this framework promises simplicity and power, achieving what CoreData had not previously accomplished.