How to Use Decimal128 in Loopback Via REST Api

Question

I would like to utilise the MongoDB Decimal128 Data type in loopback. Note: I don't want to use the Number type.

My model:

{
  "name": "Mongoproduct",
  "options": {
    "validateUpsert": true,
    "strictObjectIDCoercion": true,
    "relations": {},
    "mongodb": {
      "collection": "products",
      "allowExtendedOperators": true
    }
  },
  "properties": {
    "id": {
      "type": "String",
      "required": true,
      "length": null,
      "precision": null,
      "scale": null
    },
    "sku": {
      "type": "String",
      "required": false,
      "length": 50,
      "precision": null,
      "scale": null,
    },
    "buyprice": {
      "type": "object",
      "mongodb": {
        "dataType": "Decimal128"
      }
    },
  }
  "validations": [],
  "relations": {},
  "acls": [],
  "methods": {}
}

If I query the data through the REST explorer , a record will look something like this:

{
    "id": "5b41a6ac1afe940d900cba75",
    "sku": "shGHYB12-60-LOZ",
    "buyPrice": {
      "$numberDecimal": "20.4927"
    },
}

If I try and save the same data through a REST Put request , I get the following:

{
  "error": {
    "statusCode": 500,
    "name": "MongoError",
    "message": "The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.$numberDecimal' is not valid for storage.",
    "driver": true,
    "index": 0,
    "code": 52,
    "errmsg": "The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.$numberDecimal' is not valid for storage.",
    "stack": "MongoError: The dollar ($) prefixed field '$numberDecimal' in 'buyPrice.$numberDecimal' is not valid for storage.\n    at Function.MongoError.create (C:\\node\\ztest\\ztest_data\\node_modules\\mongodb-core\\lib\\error.js:31:11)\n    at toError (C:\\node\\ztest\\ztest_data\\node_modules\\mongodb\\lib\\utils.js:139:22)\n    at C:\\node\\ztest\\ztest_data\\node_modules\\mongodb\\lib\\collection.js:1059:67\n    at C:\\node\\ztest\\ztest_data\\node_modules\\mongodb-core\\lib\\connection\\pool.js:469:18\n    at process._tickCallback (internal/process/next_tick.js:61:11)"
  }
}

I have tried a number of things , different MongoDB types ( decimal , Decimal128 , NumberDecimal etc ) . I have tried putting allowExtendedOperators in the datasource config .

According to the loopback docs https://loopback.io/doc/en/lb3/MongoDB-connector.html#type-mappings:

Type conversion is mainly handled by Mongodb. See ‘node-mongodb-native’ for details

And According to the Native types https://docs.mongodb.com/manual/reference/bson-types/ I should be able to specify "decimal". ( I am using Mongodb 4.0 )

Any help is greatly appreciated.

Banter

Can you please add more information about how you are trying to save the data? Thanks! – Scyphozoan

@Scyphozoan Just posting through postman , exposing the Data as a REST API. When the data is a number it works fine , but the REST API generated from loopback should render the number as a number , not an object ( and yes I have tried using an object type in loopback but with no success ) – Banter

Have you tried using mixins? – Surely

Answer 1

As you are using Node.js, you can use mongoose to easily achieve what you are looking for. Mainly Loopback does not any other datatype than the Number (see here). I think here's what you can do.

You can do it in this way:

var mongoose = require('mongoose');

var testModel = mongoose.Schema({
    "buyprice": {
        "type": mongoose.Schema.Types.Decimal128
    }
}); 
// I have added only the Decimal128 field, you can define your schema here.

const Col = mongoose.model(`test`, testModel);

Col.create({ buyprice: '0.78' }).
    then(doc => console.log('Document: ', doc.toObject())).
    catch(error => console.error(error));

This will output:

Document:  { _id: 5b4ee53c95eeb452b4239eaf,
  buyprice:
   Decimal128 {
     _bsontype: 'Decimal128',
     bytes: <Buffer 4e 00 00 00 00 00 00 00 00 00 00 00 00 00 3c 30> },
  __v: 0 }

Read more.

Hope this helps you!!

Leatherette

sorry , I am after Loopback specifically @jack – Banter

Then, as far as I know, you will get Number type. – Leatherette