Graphql: I cannot stop the Node execution and return the Error (Business Error)

Question

I’m trying to create some queries and mutations, on Node with Graphql. I’ve tried how to solve the problem and I can’t find a solution. I wonder if someone could help me?

In the project I put the dependencies graphql-yoga and Mongoose.

I’m setting up a Mutation that "draws" money from an "account". I can execute by decreasing the value of the balance in the database. The problem is when you try to withdraw larger amount than the account balance. I needed at that time to show error that you do not have enough balance.

The Application is only displaying NULL balance, and does not display the error message. They know how to include in the Mutation return??

Everything else is working.

Below the code of the file resolvers.js (in Mutation withdraw, after itentify the insufficient balance error, I error, the application leaves the stream and enters the catch. But I don’t know how to log in to the error message. I only played on the console.

const Conta = require("./Conta");
let newSaldo;

module.exports = {
  Query: {
    contas: () => Conta.find(),
    conta: (root, { numero }) => Conta.findOne({ numero }),
  },

  Mutation: {
    createConta: (root, { numero, saldo, cliente }) => Conta.create({ numero, saldo, cliente }),

    depositar: (root, { numero, valor }) => Conta.findOne({numero})
                                            .then(() => Conta.updateOne({numero},{$inc:{saldo : valor}}))
                                            .then(() => Conta.findOne({numero})),

    sacar: (root, { numero, valor }) => Conta.findOne({numero})
                                        .then(value => {
                                            newSaldo = value.saldo
                                            if (valor > value.saldo) {
                                                throw new Error("Saldo Insuficiente")
                                            }
                                            else{
                                                newSaldo = value.saldo - valor
                                            }
                                        }) 
                                        .then(() => Conta.updateOne({numero},{$set:{saldo: newSaldo}}))
                                        .then(() => Conta.findOne({numero}))
                                        .catch((err) => console.log(err))                  
  },
}

schema.graphql file

type Conta {
  id: ID!
  numero: String!
  saldo: Float!
  cliente: String!
}

type Query {
  contas: [Conta!]
  conta(numero: Int!): Conta
}

type Mutation {
  createConta(numero: Int!, saldo: Float!, cliente: String!): Conta
  depositar(numero: Int!, valor: Float!): Conta
  sacar(numero: Int!, valor: Float!): Conta
}

Below the execution of Mutation, with return, to an account that does not have enough balance. Displaying NULL Balance. I need to return the error message on this screen. They can help??

Answer 1

Mutation can only return something in the format that was set within your schema, when you bump into an error, the return will be null and next to it a list of errors that occurred, will have the following format:

{
  "data": {
    "sacar": null
  },
  "errors": [
    {
      "message": "Saldo Insuficiente",
      "locations": [
        {
          "line": 2,
          "column": 3
        }
      ],
      "path": [
        "sacar"
      ]
    }
  ]
}

In order for graphql to know that the error has occurred you need to let the error go up:

const Conta = require("./Conta");
let newSaldo;

module.exports = {
    Query: {
        contas: () => Conta.find(),
        conta: (root, {
            numero
        }) => Conta.findOne({
            numero
        }),
    },

    Mutation: {
        createConta: (root, {
            numero,
            saldo,
            cliente
        }) => Conta.create({
            numero,
            saldo,
            cliente
        }),

        depositar: (root, {
                numero,
                valor
            }) => Conta.findOne({
                numero
            })
            .then(() => Conta.updateOne({
                numero
            }, {
                $inc: {
                    saldo: valor
                }
            }))
            .then(() => Conta.findOne({
                numero
            })),

        sacar: (root, {
                numero,
                valor
            }) => Conta.findOne({
                numero
            })
            .then(value => {
                newSaldo = value.saldo
                if (valor > value.saldo) {
                    throw new Error("Saldo Insuficiente")
                } else {
                    newSaldo = value.saldo - valor
                }
            })
            .then(() => Conta.updateOne({
                numero
            }, {
                $set: {
                    saldo: newSaldo
                }
            }))
            .then(() => Conta.findOne({
                numero
            }))
    },
}

Remove the catch is enough, here a functional example, here the source code for reference

Note: I did not implement the bank part, the example works with the following Mutation:

mutation {
  sacar(numero: 100, valor: 100) {
    saldo
  }
}

---

mutation {
  sacar(numero: 100, valor: 101) {
    saldo
  }
}