4. Running code generation
4m

Overview

Now that we have both a schema and a file, it's time to run code generation.

In this lesson, we will:

  • Run the codegen command
  • Add the generated code to our project
  • Examine how the code changes when we alter our

Running code generation

To run code generation run the following command in a terminal opened to your project directory:

./apollo-ios-cli generate

In Finder, you should now see a new RocketReserverAPI folder in your project directory which contains the Swift package with your generated source code.

📦 starter
┣ 📂 RocketReserver
┣ 📂 RocketReserver.xcodeproj
┣ 📂 RocketReserverAPI
┣ 📄 apollo-codegen-config.json
┣ 📄 apollo-ios-cli
┗ 📂 graphql

Add the generated SPM package to your project

With the code generated, next we need to add the generated SPM package to the project.

The default configuration for code generation creates a new Swift package for the schema module and . For more information on code generation such as different module types you can generate or different ways to run code generation see the documentation.

  1. In Xcode go to File > Add Package Dependencies..., in the dialog select Add Local...

    The Package Dependencies modal opened, highlighting Add Local Package

  2. Select the RocketReserverAPI folder in the file dialog, then click Add Package.

    The RocketReserverAPI folder in the file system

    Add it to the app target.

    Adding the RocketReserverAPI to project as target

  3. You should now see the RocketReserverAPI package included in your project.

    The RocketReserverAPI package in local dependencies

Great! Let's take a look at what we added.

Task!

Examine the generated code

In the Xcode project hierarchy, find RocketReserverAPI under Dependencies. Drill down to /Sources/Operations/Queries/LaunchListQuery.graphql.swift.

The LaunchListQuery generated file in the RocketReserverAPI dependency

That generated file defines a root class, LaunchListQuery, with many nested structs below it. If you compare the structs to the JSON data returned in , you see that the structure matches. These structs include properties only for the that your requests.

LaunchListQuery.graphql
# ... other structs
public struct Launch: RocketReserverAPI.SelectionSet {
  public let __data: DataDict
  public init(_dataDict: DataDict) { __data = _dataDict }
  public static var __parentType: any ApolloAPI.ParentType { RocketReserverAPI.Objects.Launch }
  public static var __selections: [ApolloAPI.Selection] { [
    .field("__typename", String.self),
    .field("id", RocketReserverAPI.ID.self),
    .field("site", String?.self),
  ] }
  public var id: RocketReserverAPI.ID { __data["id"] }
  public var site: String? { __data["site"] }
}

Let's see how this generated file changes when we alter our LaunchList . Jump back into LaunchList.graphql, in our project's main graphql file. Let's comment out the id , using a #.

query LaunchList {
  launches {
    cursor
    hasMore
    launches {
      # id
      site
    }
  }
}

Save the file, then open up your terminal. Let's rerun the codegen command.

./apollo-ios-cli generate

Now let's check out the results in LaunchListQuery.graphql, deep in the RocketReserverAPI dependency.

LaunchListQuery.graphql
# ... other structs
public struct Launch: RocketReserverAPI.SelectionSet {
  public let __data: DataDict
  public init(_dataDict: DataDict) { __data = _dataDict }
  public static var __parentType: any ApolloAPI.ParentType { RocketReserverAPI.Objects.Launch }
  public static var __selections: [ApolloAPI.Selection] { [
    .field("__typename", String.self),
    .field("site", String?.self),
  ] }
  public var site: String? { __data["site"] }
}

The innermost Launch now only includes the built-in __typename and the requested site property—the id , because we commented it out, is nowhere to be found! This gives us a really good idea of how the codegen process outputs exactly the code we'll need to make our functional—nothing more, and nothing less.

We actually do want to keep the id , so let's uncomment it in LaunchList.graphql and re-run code generation to restore the property.

Task!

Up next

Now that you've generated code and had a chance to see what's in there, it's time to get everything working end to end! Next, we'll execute the .

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