Update transaction value in mongodb

Question

I'm making a Mern project and I need to update two fields in a mongo db record.

I have two fields, one is an array of objects called wallets and the other is transactions.

I get an object from the frontend that includes the amount, index of the wallet where the transaction was made, because wallets are arrays of objects in mongo.

Now I need to subtract the transaction amount from the wallet. How to do this I have written a controller in node.js but it is not doing anything.

The object I receive from the front end if..

transaction = { amount: '50', wallet: 0, type: 'expense', description: 'kmop' };

My Node js controller is...

module.exports.addTransaction = async (req, res) => {
  const transaction = req.body;
  const {wallet} = transaction;

  try {
      const walletName = `Wallets.${wallet}.amount`
      await UserModel.findOneAndUpdate(
        { email: email },
        {  $inc: { walletName : -transaction.amount}   ,
          $push: { transactions: { $each: [transaction], $position: 0 } } }
      );
      res.send({stat: true});
    } 
    else {
      console.log(data)
      res.send({ stat: false });
    }
  } catch (err) {
    console.log("err",err)
    res.send({ stat: false, err: err.message });
  }
};

My mongo database records--

{"_id":{"$oid":"64a5a396ec152ab4f5e1c60c"},
"firstName":"Vinayak",
"lastName":"Pandey",
"email":"abc@123.com",
"password":"b$dpAmLPa9imDKn3qeyhZ/hOwolO6NOYVwNvVgBc9PY8XZZ3n4WYh/O",
"Wallets":[{"name":"paytm","amount":500},
           {"name":"hdfc","amount":5000},
           {"name":"test","amount":3020}]

Suppose I made a transaction of 50 rupees from namde paytm wallet, so what I want is The amount in the object with name paytm should be reduced by rs-50 so initially it is After processing, rs500 should become rs450....

Answer 1

To apply the $inc code> operator at the element of the array. We should use dot notation to specify In embedded documents or arrays,

Location $

db.collection.update({
  email: "abc@123.com",
  "Wallets.name": "paytm"
},
{
  "$inc": {
    "Wallets.$.amount": -50
  }
})

mongoplayground

enter:

[
  {
    "_id": "64a5a396ec152ab4f5e1c60c",
    "firstName": "Vinayak",
    "lastName": "Pandey",
    "email": "abc@123.com",
    "password": "b$dpAmLPa9imDKn3qeyhZ/hOwolO6NOYVwNvVgBc9PY8XZZ3n4WYh/O",
    "Wallets": [
      {
        "name": "paytm",
        "amount": 500
      },
      {
        "name": "hdfc",
        "amount": 5000
      },
      {
        "name": "test",
        "amount": 3020
      }
    ]
  }
]

Output:

[
  {
    "Wallets": [
      {
        "amount": 450,
        "name": "paytm"
      },
      {
        "amount": 5000,
        "name": "hdfc"
      },
      {
        "amount": 3020,
        "name": "test"
      }
    ],
    "_id": "64a5a396ec152ab4f5e1c60c",
    "email": "abc@123.com",
    "firstName": "Vinayak",
    "lastName": "Pandey",
    "password": "b$dpAmLPa9imDKn3qeyhZ/hOwolO6NOYVwNvVgBc9PY8XZZ3n4WYh/O"
  }
]

---

renew

Update an array element using a specific array index:

const idx = 1;
db.users.updateOne(
    {
        email: 'abc@123.com'
    },
    {
        $inc: {
            [`Wallets.${idx}.amount`]: -50,
        },
    },
);