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How to Integrate Graphql Query In Kotlin?

6 minutes read

To integrate a GraphQL query in Kotlin, you can use a library like Apollo Android that provides tools to generate query classes based on your GraphQL schema. This makes it easier to create and execute GraphQL queries in your Kotlin code. First, you need to define your GraphQL schema using a tool like Apollo CLI or GraphQL Code Generator. Then, you can use the generated query classes in your Kotlin code to create and execute GraphQL queries. Remember to handle the results of the queries and any errors that may occur during the process. By following these steps, you can seamlessly integrate GraphQL queries in your Kotlin application.


How to use subscriptions in GraphQL queries in Kotlin?

To use subscriptions in GraphQL queries in Kotlin, you can follow these steps:

  1. Define a subscription in your GraphQL schema. This can be done using the subscription keyword in your schema definition language (SDL). For example:
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type Subscription {
  newPost: Post
}


  1. Create a subscription resolver on your GraphQL server. This resolver will define the logic for what happens when a client subscribes to the newPost subscription. This can be implemented using Apollo Server, GraphQL Java or any other GraphQL server library.
  2. In your Kotlin client code, you can use a GraphQL client library like Apollo Android to subscribe to the newPost subscription. Here's an example of how you can do this using Apollo Android: 
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val apolloClient = ApolloClient.builder()
    .serverUrl("https://your-graphql-api.com")
    .build()

val subscriptionCallback = object : ApolloCall.Callback<Subscription.Root>() {
    override fun onResponse(response: Response<Subscription.Root>) {
        // Handle subscription response
    }

    override fun onFailure(e: ApolloException) {
        // Handle subscription failure
    }
}

apolloClient.subscribe(NewPostSubscription.builder().build()).enqueue(subscriptionCallback)


  1. When the server publishes a new post, the onResponse method in the subscription callback will be called with the new post data. You can then update your UI or perform any other actions based on the subscription data.


Overall, subscriptions in GraphQL allow clients to receive real-time updates from the server, making it a powerful feature for building interactive applications. By following these steps, you can use subscriptions in GraphQL queries in Kotlin effectively.


How to handle authorization in GraphQL queries in Kotlin?

In order to handle authorization in GraphQL queries in Kotlin, you can use middleware or custom directives.

  1. Middleware: Middleware is a way to intercept and handle requests before they reach the resolver. You can create a middleware function that checks the authorization of the user before allowing the request to reach the resolver. Here is an example of how you can implement middleware in Kotlin:
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val schema = Schema.new {
    query("currentUser") {
        String
    }
}

val middleware = Middleware { query ->
    val context = query.context as CustomContext
    if (!context.isAuthenticated) {
        throw UnauthorizedException("User is not authenticated")
    }
    query
}

schema.middlewares.add(middleware)


  1. Custom Directives: Another way to handle authorization in GraphQL queries is by using custom directives. Directives allow you to selectively apply logic to parts of your schema based on metadata. You can create a custom directive that checks the authorization of the user before executing a specific field or resolver. Here is an example of how you can create a custom directive in Kotlin:
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val schema = Schema.new {
    directive("auth") { directive ->
        directive.onField { field ->
            field.description("Check if user is authorized to access this field")
            field.resolve { env ->
                val context = env.getCustomContext() as CustomContext
                if (!context.isAuthenticated) {
                    throw UnauthorizedException("User is not authenticated")
                }
                env.proceed()
            }
        }
    }
}


You can then apply the custom directive to specific fields in your schema like this:

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val schema = Schema.new {
    query("currentUser") {
        String.directive("auth")
    }
}


By using middleware or custom directives, you can easily handle authorization in GraphQL queries in Kotlin and ensure that only authorized users can access certain parts of your schema.


What is the difference between GraphQL queries and REST API calls in Kotlin?

The main difference between GraphQL queries and REST API calls in Kotlin is in how they retrieve and manipulate data from a server.

  1. GraphQL queries:
  • With GraphQL, clients can request exactly the data they need and nothing more, reducing over-fetching and under-fetching of data.
  • Clients can request multiple resources in a single query, reducing the number of network requests.
  • GraphQL queries are typically written in a GraphQL query language, which allows for complex and nested queries.
  • GraphQL uses a single endpoint for all operations, making it easier to manage and maintain.
  1. REST API calls:
  • In REST API calls, clients typically interact with multiple endpoints to retrieve different resources, leading to over-fetching of data.
  • REST API calls follow a predefined structure, such as GET, POST, PUT, DELETE, etc., for different operations.
  • REST API calls can be less flexible for querying specific data as clients must work with the structure provided by the server.
  • REST APIs use different endpoints for different resources, which can lead to higher network latency and more complex client-server interactions.


In summary, GraphQL queries offer more flexibility, efficiency, and control over the data requested from a server compared to traditional REST API calls. However, the choice between GraphQL and REST API calls ultimately depends on the specific requirements and constraints of the project.


How to work with GraphQL schemas in Kotlin?

Working with GraphQL schemas in Kotlin involves defining your schema using GraphQL SDL (Schema Definition Language) and using a library like GraphQL Java to parse the schema, generate classes, and execute queries against the schema.


Here is a step-by-step guide on how to work with GraphQL schemas in Kotlin:

  1. Define your GraphQL schema using GraphQL SDL. Here is an example of a simple schema defining a query and a single field:
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schema {
  query: Query
}

type Query {
  hello: String
}


  1. Create a Kotlin class to represent your schema. You can use data classes to define the types in your schema:
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data class Query(val hello: String)


  1. Use the GraphQL Java library to parse your schema and generate the necessary classes. Add the following dependencies to your build.gradle file:
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dependencies {
    implementation 'com.graphql-java:graphql-java:16.0'
    implementation 'com.graphql-java:graphql-java-tools:6.0.14'
}


  1. Create a GraphQL schema using the SDL and classes defined in steps 1 and 2:
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val schema = new SchemaParser().parse(
    """
    type Query {
      hello: String
    }
    """
)


  1. Define a data fetcher to handle queries on the schema:
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val dataFetcher = DataFetcher<String> { environment -> "Hello, world!" }
val wiring = StaticWiring.newWiring().dataFetcher("Query.hello", dataFetcher)

val executableSchema = new SchemaGenerator().makeExecutableSchema(schema, wiring)


  1. Use the executionInputBuilder to execute queries against the schema:
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val executionInput = ExecutionInput.newExecutionInput()
    .query("{ hello }")
    .build()

val result = GraphQL.newGraphQL(executableSchema).build().execute(executionInput)

println(result)


This is a basic example of working with GraphQL schemas in Kotlin. Depending on the complexity of your schema, you may need to define more types, queries, and mutations in your schema and data fetchers to handle them.


What is the best way to structure a GraphQL query in Kotlin?

When structuring a GraphQL query in Kotlin, it is common to use a library such as Apollo Android to handle the query building and execution. Here is an example of how you can structure a GraphQL query using Apollo Android:

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val query = GetBooksQuery.builder().build()
apolloClient.query(query)
    .enqueue(object : ApolloCall.Callback<GetBooksQuery.Data>() {
        override fun onResponse(response: Response<GetBooksQuery.Data>) {
            // Handle the response here
        }

        override fun onFailure(e: ApolloException) {
            // Handle the error here
        }
    })


In this example, we are using the Apollo Android library to build and execute a GraphQL query for fetching books. The GetBooksQuery class is generated by Apollo Android based on the GraphQL schema. We use the apolloClient instance to execute the query and handle the response and potential errors in the onResponse and onFailure callbacks, respectively.


This structured approach helps to maintain a clean and organized codebase when working with GraphQL queries in Kotlin.

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