Spring Boot + Kotlin + GraphQL + MongoDB — Part 2: Mutations

Hack the stack.

Part 1: Queries (Spring Boot + Kotlin + GraphQL + MongoDB)

Most discussions of GraphQL focus on data fetching, but any complete data platform needs a way to modify server-side data as well.

In REST, any request might end up causing some side-effects on the server, but by convention it’s suggested that one doesn’t use GET requests to modify data. GraphQL is similar - technically any query could be implemented to cause a data write. However, it's useful to establish a convention that any operations that cause writes should be sent explicitly via a mutation.

• This post is a sequel to Spring Boot + Kotlin + GraphQL + MongoDB — Part 1.
• Demo project repository is available at GitHub.

Creating your first GraphQL mutation

In the previous post, I tried to explain how one can fetch Person object from the MongoDB using GraphQL queries. In this post we are going to insert the Person object into a database with the GraphQL mutations. Let’s go!

Update PersonDao

createPerson(name:) method is appended to PersonDao class which passes name argument to the save(S) method from PersonRepository. As PersonRepository implements CrudRepository, so we got save(S) method for free.

GraphQL input

Read about GraphQL input types.

Create person_input.graphqls file inside resources/graphql/input directory with following content:

input PersonInput {
    name: String!
}

and the associated data class named PersonInput inside graphql/input package:

GraphQL mutation

Create mutation.graphqls inside resources/graphql directory with following content:

type Mutation {
    # Creates person
    personCreate(input: PersonInput!): Person!
}

Same method must exist in GraphQLMutationResolver subclass, which is a Spring BootComponent. A good place to put it is in the graphql package:

PersonDao is our connection to a data layer. Passing a name should create a Person record in the database.

We’re done coding!

Executing mutation

Run mvn spring-boot:run and execute some mutations in the GraphiQL interface!

mutation {
  personCreate(name: "Joey Tribbiani") {
    id
    name
  }
}

should return something like:

{
  "data": {
    "personCreate": {
      "name": "Joey Tribbiani",
      "id": "b6ff8f21-923f-43a4-b84a-9e81705c8159"
    }
  }
}

Congratulations, you have successfully connected GraphQL mutations to the MongoDB!

aronbalog/SpringGraphQLExample