1. Getting Started in GraphQL With Spring Boot in Java

We are just trying to integrate GraphQL with Spring Boot. I am assuming that you have some knowledge about GraphQL and Spring Boot. We are creating controllers for CRUD operations using GraphQL. I have created a sample spring boot microservice for crud operation on Person object to understand the concept.

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In GraphQL read operations means query which can be denoted by @QueryMapping annotation.
create/update/delete operations means mutations which are denoted by @MutationMapping annotation.

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Data passed using Postman tool to the controller, can be captured using @Argument annotation provided by spring-boot-graphql, it's alternative of @RequestParam for GraphQL.

2. GitHub repo for working project

Follow this link for code on Github

3. Dependencies needed

Java 8 version is used with Spring boot framework

4. Mapping between table, graphql schema & java class

5. GraphQL Schema:-

Write following schema in schema.graphqls file under resources/graphql folder in the spring boot project

type Person {
  id: ID!
  name: String!
  country: String!
}

# comments can be written with # symbol
type Query {
  # Retrieve one person by ID
  getPerson(id: ID!): Person

  # Retrieve all persons
  getAllPersons: [Person!]!
}

type Mutation {
  # Add a new person
  addPerson(name: String, country: String): Person
  # we can write like this also
  # addPerson(input: AddPersonInput!): Person

  # Update a person by ID
  updatePerson(id: ID!, name: String, country: String): Person
  # we can write like this also
  # updatePerson(id: ID!, input: UpdatePersonInput!): Person

  # Delete a person by ID
  deletePerson(id: ID!): Person
}

# if we want to use input as argument while adding/updating person
# or else not needed
input AddPersonInput {
  name: String!
  country: String!
}

# if we want to use input as argument while adding/updating person
# or else not needed
input UpdatePersonInput {
  name: String
  country: String
}

6. Java Code

class Person {
    private long id;
    private String name;
    private String country;
}

@RestController
public class PersonController {
    @Autowired
    private PersonRepository personRepository;

    // get all persons
    @QueryMapping("allPersons")
    public List<Person> persons(){
        return personRepository.findAll();
    }

    //get one person
    @QueryMapping
    public Person person(@Argument int id){
        // use optional to get data, refer github repo
        return personRepository.findById((long)id); 
    }

    //add one person
    @MutationMapping("addPerson")
    public Person person(@Argument String name, @Argument String country){
       // refer github for correct code, this is just for understanding
       Person p = new Person(name, country);
       personRepository.save(p);
    }
}

7. Postman Request

# postman request
url - http://localhost:8080/graphql

# getPerson(id: ID!): Person
query{
  getPerson(id: "1") {
    name
    country
  }
}

# getAllPersons: [Person!]!
query{
  getAllPersons {
    persons {
        name
        country
    }
  }
}

# addPerson(name: String, country: String): Person
mutation{
  addPerson(name: "ABD", country: "SA"){
    id # this will be generated automatically for newly added person
    name
    country
  }
}