Integrating GraphQL in Spring boot Project guideline

In this blog, we will learn graphql API in spring boot and see graphql schema, query, etc.

we are going to implement graphql in the existing spring boot project that we have created in the previous blog spring-boot-JPA-integration-with-SQLite.

GraphQL API tutorial in Spring boot

What is GraphQL?

GraphQL is a query language for API not specific to any database or framework developed by Facebook, GraphQL client uses graphQL query( specific which fields we are looking for in response) to fetch data from the server.

In GraphQL, the client can get all details in a single request instead of multiple calls to the backend like REST API.

Graphql Maven dependency

we need to add the below dependency in the pom.xml file which provides support for creating graphQL API in spring boot.

<dependency>
    <groupId>com.graphql-java</groupId>
    <artifactId>graphql-spring-boot-starter</artifactId>
    <version>5.0.2</version>
</dependency>
<dependency>
    <groupId>com.graphql-java</groupId>
    <artifactId>graphql-java-tools</artifactId>
    <version>5.2.4</version>
</dependency>
<!-- GraphiQL -->
<dependency>
    <groupId>com.graphql-java</groupId>
    <artifactId>graphiql-spring-boot-starter</artifactId>
    <version>5.0.2</version>
</dependency>

By default, the GraphQL Service will be accessible on /graphql URL and will accept POST requests with the GraphQL Payload. If required, you can modify this endpoint in our application.properties file.

Create GraphQl Schema

First, we need to create a graphql schema that contains the graphql query and object type (similar to class) that return in the response.

graphQL API tutorial schema diagram

The graphql server exposes this schema to the graphql client describing the available query and structure of object data (class and their field) based on schema the client creates a query and sends it to the server for execution.

create a schema.graphqls file inside the src/main/resource folder.

schema {
  query: Query
}

type Query {
  getAllEmployee: [Employee]
  getEmployeeById(id: Int): Employee
}

type Employee {
  id: ID
  name: String
  jobTitle: String
  mobileNo: String
  joinedDate: String
  gender: String
  department: Department
  project: Project
}

type Department {
  id: ID
  name: String
}

type Project {
  id: ID
  name: String
}

Here the Employee, Department, and Project are graphql object types. The [Employee] means an array of employee objects.

The getAllEmployee and getEmployeeById are queries the client use to fetch object data from the graphql server.

we can have several separate schema files to organize the schemes, e.g. we can have employee.graphqls, project.graphqls, etc.

There can be only one query and mutation type describing all operations, if there are separate schema files each containing its own query and mutation then use extend keyword so all queries and mutation are added together.

Create JPA repository

let's create a JPA repository to get employee details from the SQLite database.

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.stereotype.Repository;

import com.example.graphql.model.Employee;

@Repository
public interface EmployeeRepository extends JpaRepository<Employee, Integer> {

}

Create Query Resolver

Now create a class GraphQLService that implements GraphQLQueryResolver, this class contains the actual implementation of a query defined in the graphql schema.

The query name defined in schema and method name must be the same.

Please see the complete post here