Migrating from REST to GraphQL in Android

What is GraphQL?

GraphQL is a query language for fetching and mutating data from a backend service. Unlike REST, which has multiple endpoints for retrieving and updating data, GraphQL has only one entry point (URL) for all operations. This is made possible by GraphQL queries, which allow you to specify exactly what data you need.

Benefits of GraphQL

GraphQL addresses two major issues with REST: over-fetching and under-fetching. With GraphQL, the client can fetch only the data it needs, reducing the amount of data transferred over the network. This results in faster load times and improved performance.

Setting up the Starter Project

To demonstrate the migration process, we’ll use a GitHub project that utilizes the GitHub REST API. Our project is written in Kotlin and uses Jetpack Compose, Hilt for dependency injection, and Pagination with the Paging Library 3.

Migrating to GraphQL

To migrate our project to GraphQL, we’ll need to:

• Replace Retrofit with ApolloClient
• Define GraphQL Schema and Queries
• Refactor GitHub API
• Update GithubUserSource

Defining GraphQL Schema and Queries

We’ll create a GraphQL schema that defines the types of data we can fetch from the GitHub API. We’ll then define queries that specify exactly what data we need.

type Query {
  users(first: 10): [User]
}

type User {
  id: ID!
  name: String!
  avatarUrl: String!
}

Refactoring GitHub API

We’ll update our GitHub API to use ApolloClient and execute GraphQL queries. We’ll define a GetUsersQuery that fetches a list of users from the GitHub GraphQL API.

import com.apollographql.apollo3.ApolloClient
import com.apollographql.apollo3.api.Query

class GitHubApi(private val apolloClient: ApolloClient) {
  suspend fun getUsers(): List {
    val response = apolloClient.query(GetUsersQuery()).execute()
    return response.data.users
  }
}

Updating GithubUserSource

We’ll update our pagination source to use ApolloClient and execute GraphQL queries. We’ll define a load() method that fetches users from the server and returns a LoadResult.Page object.

import androidx.paging.PagingSource
import androidx.paging.PagingState

class GithubUserSource(private val api: GitHubApi) : PagingSource<int, user="">() {
  override suspend fun load(params: LoadParams): LoadResult<int, user=""> {
    val users = api.getUsers()
    return LoadResult.Page(users, null, null)
  }

  override fun getRefreshKey(state: PagingState<int, user="">): Int? {
    return state.anchorPosition
  }
}
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