introduction.md

Getting started with genqlient

This document describes how to set up genqlient and use it for simple queries. See also the full worked example, the FAQ, and the rest of the documentation.

Step 1: Download your schema

You want the schema in GraphQL Schema Definition Language (SDL) format. For example, to query the GitHub API, you could download the schema from their documentation. Put this in schema.graphql.

Step 2: Write your queries

Next, write your GraphQL query. This is often easiest to do in an interactive explorer like GraphiQL; the syntax is just standard GraphQL syntax and supports both queries and mutations. Put it in genqlient.graphql:

query getUser($login: String!) {
  user(login: $login) {
    name
  }
}

Step 3: Run genqlient

Now, run go run github.com/Khan/genqlient --init. This will create a configuration file, and then run genqlient to produce a file generated.go with your queries.

Step 4: Use your queries

Finally, write your code! The generated code will expose a function with the same name as your query, here

func getUser(ctx context.Context, client graphql.Client, login string) (*getUserResponse, error)

As for the arguments:

• for ctx, pass your local context (see go doc context) or context.Background() if you don't need one
• for client, call graphql.NewClient, e.g. graphql.NewClient("https://your.api.example/path", http.DefaultClient)
• for login, pass your GitHub username (or whatever the arguments to your query are)

The response object is a struct with fields corresponding to each GraphQL field; for the exact details check its GoDoc (perhaps via your IDE's autocomplete or hover). For example, you might do:

ctx := context.Background()
client := graphql.NewClient("https://api.github.com/graphql", http.DefaultClient)
resp, err := getUser(ctx, client, "benjaminjkraft")
fmt.Println(resp.User.Name, err)

Now run your code!

Step 5: Repeat

Over time, as you add or change queries, you'll just need to run github.com/Khan/genqlient to re-generate generated.go. (Or add a line //go:generate go run github.com/Khan/genqlient in your source, and run go generate.) If you're using an editor or IDE plugin backed by gopls (which is most of them), keep generated.go open in the background, and reload it after each run, so your plugin knows about the automated changes.

If you prefer, you can specify your queries as string-constants in your Go source, prefixed with # @genqlient -- at Khan we put them right next to the calling code, e.g.

_ = `# @genqlient
  query getUser($login: String!) {
    user(login: $login) {
      name
    }
  }
`

resp, err := getUser(...)

(You don't need to do anything with the constant, just keep it somewhere in the source as documentation and for the next time you run genqlient.) In this case you'll need to update genqlient.yaml to tell it to look at your Go code.

All the filenames above, and many other aspects of genqlient, are configurable; see the full documentation for usage guides, reference information, and documentation on how to contribute to genqlient.