Using GraphQL in Swift: Apollo and Relay Libraries for iOS/macOS

GraphQL Libraries for Swift (iOS/macOS): Complete Guide

GraphQL is a modern query language for APIs that allows clients to request only the data they need. For Swift developers building applications for iOS and macOS, there are powerful libraries that simplify integration with GraphQL servers. In this article, we will look at two main libraries: Apollo iOS and Relay (via Swift wrappers), and provide practical code examples.

What is GraphQL and why is it important for Swift?

GraphQL solves the problem of overfetching and underfetching data that often occurs when using REST APIs. In Swift, this is especially relevant for mobile applications, where every extra kilobyte of data can affect performance and loading time. Key advantages of GraphQL for iOS/macOS:

• Flexible queries — the client decides which fields to receive
• Strong typing — GraphQL schemas automatically generate Swift types
• Subscription support — real-time updates via WebSocket
• Single entry point — one endpoint for all queries

Apollo iOS Library

Apollo iOS is the most popular GraphQL library for Swift, developed by Apollo GraphQL. It provides a complete set of tools for working with GraphQL: from code generation to caching and error handling.

Installing Apollo iOS

For installation, use Swift Package Manager. Add the dependency to your Package.swift:

// swift-tools-version:5.7import PackageDescription

let package = Package(    name: "MyApp",    dependencies: [        .package(url: "https://github.com/apollographql/apollo-ios.git", from: "1.0.0")    ],    targets: [        .target(name: "MyApp", dependencies: [            .product(name: "Apollo", package: "apollo-ios")        ])    ])

You can also install via CocoaPods or Carthage, but SPM is the recommended method.

Setting up the Apollo Client

Create an instance of ApolloClient with the URL of your GraphQL server:

import Apollo

class NetworkManager {    static let shared = NetworkManager()        private(set) lazy var apollo: ApolloClient = {        let url = URL(string: "https://api.example.com/graphql")!        return ApolloClient(url: url)    }()}

Example query using Apollo iOS

Suppose you have a schema with a User type and fields id, name, email. Let's create a query:

import Apollo

// Define the GraphQL query (usually in a .graphql file)let query = """    query GetUser($id: ID!) {        user(id: $id) {            id            name            email        }    }"""

// Execute the queryNetworkManager.shared.apollo.fetch(query: query, variables: ["id": "123"]) { result in    switch result {    case .success(let graphQLResult):        if let user = graphQLResult.data?.user {            print("User: \\(user.name), Email: \\(user.email)")        }    case .failure(let error):        print("Error: \\(error)")    }}

Note: Apollo automatically generates Swift types for your queries (e.g., GetUserQuery) if you use its code generation tool. To do this, run apollo-ios-cli with your schema.

Mutations and Subscriptions

Apollo supports mutations (data modification) and subscriptions (real-time). Example mutation:

let mutation = """    mutation UpdateUser($id: ID!, $name: String!) {        updateUser(id: $id, name: $name) {            id            name        }    }"""

NetworkManager.shared.apollo.pe