How to execute a mutation in GraphQL?

Question

In GraphQL we have basically two types of operations: queries and mutations. While queries are well described in the documentation and there are many examples of them, I'm having a hard time to understand how to execute a mutation. Mutations obviously are update methods.

I've created very simple Node.js server:

var express = require("express");
var graphqlHTTP = require("express-graphql");
var graphql = require("graphql");
var inMemoryDatabase = require("./inMemoryDatabase").inMemoryDatabase;
var _ = require("lodash-node");

var userType = new graphql.GraphQLObjectType({
  name: "User",
  fields: {
    id: { type: graphql.GraphQLString },
    name: { type: graphql.GraphQLString }
  }
});

var queryType = new graphql.GraphQLObjectType({
  name: "Query",
  fields: {
    user: {
      type: userType,
      args: {
        id: { type: graphql.GraphQLString }
      },
      resolve: function(parent, { id }) {
        return _.find(inMemoryDatabase, { id: id });
      }
    }
  }
});

var mutationType = new graphql.GraphQLObjectType({
  name: "Mutation",
  fields: {
    user: {
      type: userType,
      args: {
        id: { type: graphql.GraphQLString },
        name: { type: graphql.GraphQLString }
      },
      resolve: function(parent, { id, name }) {
        var index = _.findIndex(inMemoryDatabase, { id: id });
        inMemoryDatabase.splice(index, 1, { id: id, name: name });
        return _.find(inMemoryDatabase, { id: id });
      }
    }
  }
});

var schema = new graphql.GraphQLSchema({
  query: queryType,
  mutation: mutationType
});

var app = express();
app.use(
  "/graphql",
  graphqlHTTP({
    schema: schema,
    graphiql: true
  })
);

var port = 9000;
if (process.env.PORT) {
  port = process.env.PORT;
}

app.listen(port);
console.log("Running a GraphQL API server at localhost:" + port + "/graphql");

In memory database is just in an array of User objects {id, name}:

var inMemoryDatabase = [
  {
    id: "31ce0260-2c23-4be5-ab78-4a5d1603cbc8",
    name: "Mark"
  },
  {
    id: "2fb6fd09-2697-43e2-9404-68c2f1ffbf1b",
    name: "Bill"
  }
];

module.exports = {
  inMemoryDatabase
};

Executing query to get user by id looks as follows:

{
 user(id: "31ce0260-2c23-4be5-ab78-4a5d1603cbc8"){
  name
 }
}

How would the mutation changing user name look like?

user_1938097 · Answer

Hey may completely be missing what you are saying, but the way that I look at a mutation is like this

I get some arguments and a field, that is the same thing as params and a path in rest, with those i do something (in your case lookup the user and update the attribute based on the arguments passed in
After That, i return something from the resolve function that will fulfill the type you specify in the type of the mutation

var mutationType = new graphql.GraphQLObjectType({
  name: "Mutation",
  fields: {
    user: {
      // You must return something from your resolve function 
      // that will fulfill userType requirements
      type: userType,
      
      // with these arguments, find the user and update them
      args: {
        id: { type: graphql.GraphQLString },
        name: { type: graphql.GraphQLString }
      },
      // this does the lookup and change of the data
      // the last step of your result is to return something
      // that will fulfill the userType interface
      resolve: function(parent, { id, name }) {
        // Find the user, Update it
        // return something that will respond to id and name, probably a user object
      }
    }
  }
});

Then with that as a context, you pass some arguments and request back a user

mutation updateUser {
  user(id: "1", name: "NewName") {
    id
    name
  }
}

In a normal production schema you would also normally have something like errors that could be returned to convey the different states of the update for failed/not found

user_3775079 · Answer

@Austio's answer was pretty close, but the proper way is:

mutation updateUser {
  user(id: "31ce0260-2c23-4be5-ab78-4a5d1603cbc8", name: "Markus") {
    id
    name
  }
}

How to execute a mutation in GraphQL?

2 Answers