Return mysql query for graphql resolver function in node-mysql

Question

I'm new to graphql and node so sorry if this is really simple but I'm trying to perform a mysql query so that the query response is returned by graphql for the client to read from. The problem I'm running into is that because node-mysql does query asynchronously, I can't get the query response directly.

After some tinkering I figured it out, new code:

var root = {
    login: function({username, password}) {
        var s = `select password from users where username='${username}'`;
        var result = sql.query(s);
        return result.then(response => {
            return password == response[0].password
        });
}

Here is the function definition for sql.query

exports.query = function(s, callback) {
    var promise = new Promise((resolve, reject) => {
        con.query(s, function(err, response) {
            if (err) throw err;
            resolve(response);
    });
});
return promise;

Graphql now return that response is not defined.

wednesdaymiko · Accepted Answer · 2017-05-09 19:07:18Z

5

I personally use mysql, but shouldn't be too much of a difference.

So I do it like this:

exports.getUser = ({ id }) => {
  return new Promise((resolve, reject) => {
    let sql = `select * from users u where u.user_id = ?`;
    sql = mysql.format(sql, [id]);
    connection.query(sql, (err, results) => {
      if (err) reject(err);
      resolve(results);
    });
  });
};

Wrap the query around a Promise, which resolves when the query is done.

Then in the resolve of a field, you just call .then on the promise and do whatever you want.

const viewerType = new GraphQLObjectType({
  name: 'Viewer',
  fields: () => ({
    user: {
      type: userType,
      args: {
        id: {
          type: GraphQLInt,
        },
      },
      resolve: (rootValue, args) => {
        return getUser({ id: args.id }).then(value => value[0]);
      },
    },
  }),
});

answered May 9, 2017 at 19:07

wednesdaymiko

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4 Comments

MacStation Over a year ago

I updated my code to do it how yours does and now graphql shows that response is not defined. Also, is there a difference between how you defined the resolve function vs how I did? I don't have anywhere in my code an instantiation of GraphQLObjectType.

wednesdaymiko Over a year ago

Your .then is not returning right. It should probably be .then((response) => password == response[0].password);

MacStation Over a year ago

Yup, just fixed it, thank you so much! On a side note, what about the difference between how you defined the resolver and how I did it? Does it matter?

wednesdaymiko Over a year ago

Hmm, not sure actually. But I think the difference is that you're hard coding in the field. So, if you want reuse the login somewhere else, creating an objecttype is a good way to go about it. But in your case above where you just verify for login only in one place with true and false, it's not necessary to create a new type.

Oversteer · Accepted Answer · 2023-01-10 18:00:58Z

I appreciate that this is an old post but I've found this topic somewhat confusing and have been investigating different approaches, both which are shown here. One is a bit less verbose then the other (getQuery). I include the code for a mutation which although largely irrelevant to this topic demonstrates how none of this promise complication applies to returning the result of a mutation, just saying.

The documentation describes another approach called promise wrappers https://github.com/sidorares/node-mysql2#using-promise-wrapper. In my case this would have needed a top level await which didn't really fit in with my needs although there are all kinds of workarounds, but I just wanted the simplest possible solution to a simple problem.

resolver.ts

import db from "db";
    
    // this is one way of doing it
    const getQuery = async (sql: string) => {
      const [rows] = await db.promise().query(sql);
      return rows;
    };
    
    // and this is another
    const getQuery2 = (sql: string) => {
      return new Promise((resolve, reject) => {
        db.query(sql, (error, results) => {
          if (error) return reject(error);
          return resolve(results);
        });
      });
    };
    
    export const resolvers = {
      Query: {
        getUsers: () => getQuery("SELECT * FROM `users`"),
      },
      Mutation: {
        userLogin: (_, { email, password }) => {
          return {
            __typename: "UserLoginResponse",
            status: "success",
            jwt: "abc123",
          };
        },
      },
    };


db.ts

import mysql2 from "mysql2";

console.log("connecting to RDS db:", process.env.DB_BOOK_IT_HOST);

export const db = mysql2.createConnection({
  host: process.env.DB_BOOK_IT_HOST,
  user: process.env.DB_BOOK_IT_USER,
  password: process.env.DB_BOOK_IT_PASSWORD,
  database: process.env.DB_BOOK_IT_DATABASE,
});

export default db;

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