How to handle error and send response in GraphQL

Question

I was starting with GraphQL and I was unable to comprehend how we can throw errors in GraphQL

I went through a couple of articles on the web but almost all of them use

Answer 1

What I have faced in one of my projects, it is hard to set the status code of the response. So, I made some custom error response to identify correct statusCode using express-graphql

Below is the example (What I have used in one of my projects):

--------app.js file--------

const graphqlHTTP = require('express-graphql')

app.use('/graphql', (req, res) => {
  graphqlHTTP({
    schema: GraphQLSchema, //A GraphQLSchema instance from GraphQL.js. A schema must be provided.
    graphiql: true,
    context: { req },
    formatError: (err) => {
      const error = getErrorCode(err.message)
      return ({ message: error.message, statusCode: error.statusCode })
    }
  })(req, res)
})

--------getErrorCode function implementation--------

const { errorType } = require('../constants')

const getErrorCode = errorName => {
  return errorType[errorName]
}

module.exports = getErrorCode

--------Constant.js file--------

exports.errorName = {
  USER_ALREADY_EXISTS: 'USER_ALREADY_EXISTS',
  SERVER_ERROR: 'SERVER_ERROR'
}

exports.errorType = {
  USER_ALREADY_EXISTS: {
    message: 'User is already exists.',
    statusCode: 403
  },
  SERVER_ERROR: {
    message: 'Server error.',
    statusCode: 500
  }
}

---

Now, we are ready to use our setup.

From your query or mutation, you need to require constant file and return custom error:

const { errorName } = require('../constant')

AddNewPersonalInfo: {
  type: userDashboardType,
  args: { 
    parameter: {
      type: userCreationlInputType
    }
  }, 
  resolve: async (parent, args, context) => {
    args.parameter.userId = context.req.headers.userId
    //Check if user info already exsist
    const checkIfUserInformationExsist = await getSelectedThingFromTable('CatsWork_personal', 'userId', `${userId}`)
    if (checkIfUserInformationExsist[0]) {
      const error = {
        code: 403, 
        message: 'User info Already exsist'
      }
      throw new Error(errorName.USER_ALREADY_EXISTS) // Here you can use error from constatnt file
    } else {
      try {
      const addLinkedinUser = await insertIntheTable('personal', payload)
      return true
      } catch (err) {
        console.error(err)
        throw new Error(errorName.SERVER_ERROR) // Here you can use error from constatnt file
      }
    }
  }
}

--------Error response--------

{
  error: [{
    "statusCode": 403,
    "message": "User is already exists."
  }],
  data: null
}

We just need to write custom error handling from FS side too.

Note:- formatError: is deprecated and replaced by customFormatErrorFn. It will be removed in version 1.0.0. You can refer customFormatErrorFn.

Hope this help!