Elixir GraphQL APIs

Introduction to GraphQL and Absinthe

GraphQL is a query language for APIs that allows clients to request exactly the data they need. It's an alternative to traditional REST APIs, offering more flexibility and efficiency. Elixir, known for its scalable and maintainable applications, uses the Absinthe library to build GraphQL APIs. Absinthe provides a robust framework for defining GraphQL schemas and executing queries.

Setting Up an Elixir Project with Absinthe

To start using Absinthe in your Elixir project, you'll need to set up a new Phoenix application. Phoenix is a web framework for Elixir that works well with Absinthe. Begin by creating a new Phoenix project:

Navigate into your project directory and add Absinthe as a dependency in your mix.exs file:

After updating your dependencies, run the following command to fetch them:

Defining a Simple GraphQL Schema

With Absinthe installed, you can define your first GraphQL schema. In this example, we'll create a simple schema that defines a User type and a query to fetch users.

This schema defines a User type with three fields: id, name, and email. It also defines a users query that will resolve to a list of users using the resolver function list_users.

Creating Resolver Functions

Resolvers are responsible for fetching the data requested by queries. Create a resolver module and define the list_users function:

The list_users function returns a hard-coded list of users. In a real application, this data might come from a database. The function returns a tuple with :ok and the list of users, which is the expected format for Absinthe resolvers.

Running the GraphQL Server

To serve your GraphQL API, you need to update your Phoenix router to include the Absinthe plug. Modify your router to add a new route for the GraphQL endpoint:

Start your Phoenix server using mix phx.server and navigate to http://localhost:4000/api/graphql to access your GraphQL API. You can use GraphiQL, a web-based IDE, to test your queries.

Testing Your GraphQL Queries

Once your server is running, you can test your GraphQL API using the following query to fetch all users:

GraphiQL or any GraphQL client can be used to execute this query. The response should include the list of users defined in your resolver.

Conclusion

In this tutorial, you learned how to build a GraphQL API using Elixir and Absinthe. You set up a Phoenix project, defined a GraphQL schema, created resolvers, and tested your API. With this foundation, you can expand your API to include more complex queries and mutations, leveraging the power of Elixir and Absinthe.