Unlock the Power of GraphQL and Kotlin
A New Era in API Development
For years, REST has been the go-to design for creating backend APIs. However, GraphQL has been gaining popularity as a viable alternative. Similarly, Kotlin has emerged as a preferred choice among Android developers, offering a more modern and expressive way of coding. But what happens when you combine the two? In this article, we’ll explore the possibilities of setting up GraphQL in Ktor and exposing an existing datasource as a GraphQL API.
What You Need to Know
Before we dive in, let’s take a quick look at the solutions we’ll be discussing. Ktor is an asynchronous framework used to create web applications, allowing developers to easily create a backend API in Kotlin for mobile or web clients. GraphQL, on the other hand, is a language for querying data, exposing data from an underlying datasource in a flexible and efficient manner.
GraphQL 101
GraphQL has three main operations: Query, Mutation, and Subscription. Query is used for fetching data, Mutation for writing data, and Subscription for fetching updates when data changes. What’s more, GraphQL is agnostic of where the actual data resides, making it a versatile choice for developers.
Kotlin and GraphQL: A Match Made in Heaven
One of the key similarities between Kotlin and GraphQL is nullability as a feature. In Kotlin, a nullable field is denoted with?, while in GraphQL, a non-nullable field is displayed as!. This shared understanding of nullability makes it easier to work with both languages.
Creating a GraphQL API
To create a GraphQL API, we’ll use the KGraphQL library to expose data as a GraphQL API. We’ll start by adding KGraphQL dependencies to our build.gradle or build.gradle.kts file. Then, we’ll create a file called KGraphQL.kt and add an extension function to Ktor’s Application.kt file.
GraphiQL Playground: The Ultimate Testing Tool
Once we’ve set up KGraphQL, we can run our application and hit the /graphql endpoint to access the GraphiQL playground. This interactive environment allows us to test our GraphQL queries during development, making it easier to debug and refine our API.
Querying and Typing
To register our Movie data class as a GraphQL output type, we’ll add it to the schema block of the KGraphQL.kt file. Then, we can create a simple query that returns the list of movies by adding the following code to our schema block.
Arguments: Adding Flexibility to Your Queries
To add an argument to the movies query, we can modify our resolver to include a parameter for limiting the number of movies returned. We can also make the argument optional by providing a default value using the withArgs closure.
Mutations: Writing Data with GraphQL
To create a mutation operation, we’ll follow a similar process to our query operation. We’ll define a mutation resolver and register it in our schema block. Then, we can run the mutation query to add a new row to our database.
Running Without Playground
Once we’ve finished developing our API, we can disable the GraphiQL playground and access our GraphQL API using a POST request. We can also customize the endpoint to something like /movies-graphql for easier access.
The Future of API Development
By combining the power of GraphQL and Kotlin, we can create robust and efficient APIs that meet the demands of modern applications. With KGraphQL, we can easily expose our underlying data sources as GraphQL API endpoints, making it easier to develop and maintain our APIs. The possibilities are endless, and we’re excited to see what you’ll build with these powerful tools.