How to find _id and verify if it has an existing key in mongoose please?

Question

I want to find user by its _id and verify if he had or not btc in his wallet?

users =
{
  "_id": "6515a3cb181eafcdd26460ce"
  "wallet": [
    {
      "btc": 0.1
    },
    {
      "bnb": 20
    }
  ]
}

I try this

const id = "6515a3cb181eafcdd26460ce"
const query = await users.findOne({ _id: id, wallet: {$in: [`btc`]} });

Answer 1

I'm not sure how your documents will be stored in terms of the btc object but this will cover you just in case the value of btc is zero ("btc": 0) or if the btc property is not there.

This will match if all conditions are true:

1. The _id is a match
2. The document has an object in the wallet array with a key btc that is not null
3. The document has an object in the wallet array with a key btc that is not equal to zero.

const id = "6515a3cb181eafcdd26460ce" 
const query = await users.findOne({
  _id: id,
  wallet: {
    $elemMatch: {
      $and: [
        {
          btc: {
            $ne: 0
          }
        },
        {
          btc: {
            $ne: null
          }
        }
      ]
    }
  }
});

See it working here. You will notice I have included a few different objects. One without the an object containing btc, one with a "btc":0, and one with a "btc":null.

Edit: If you want to update the value then you can increment the btc value using $inc and then check that the update was successful. The findOneAndUpdate method returns null if no document was found so you will know if it was unsuccessful. I have included the code below to get you started:

try {
   const user = await users.findOneAndUpdate({ _id: "6515a3cb181eafcdd26460ce",
     wallet: {
       $elemMatch: {
         $and: [
           {
             btc: {
               $ne: 0
             }
           },
           {
             btc: {
               $ne: null
             }
           }
         ]
       }
     }
   }, { $inc: {"wallet.$.btc": 0.5 }}, {new: true});

   if(!user){ //If null
      // No user found, update not successful
      // Respond to front-end
   }else{
      // Repond to front-end with success
   }
}catch(err){
   console.log(err);
   //Handle error response to front-end
}