how should i store a price in mongoose?

Question

I'm using mongoose schemas for node.js along with express-validator (which has node-validator santiziations and validators).

What's a good way to store price for an item?

I currently have

var ItemSchema = new Schema({
    name            : { type: String, required: true, trim: true }
    , price             : Number
});

Price is optional, so I have:

  if ( req.body.price ) {
    req.sanitize('price').toFloat();
    req.assert('price', 'Enter a price (number only)').isFloat();
  }

express-validator gives me isNumeric (allows 0 padding), isDecimal, and isInt...I'd rather just convert to decimal and strip all characters, so I'm always inserting 42.00 into db.

I want to allow them to enter $42.00, $42, 42, 42.00 and just store 42.00. How can I accomplish this? and still validate that I'm seeing something resembling a number, for example if they enter 'abc' I want to throw an error back to the form using req.assert.

Also, I suppose currency will eventually become an issue...

Update, I found this post which says to store price as integer in cents, so 4200 https://dba.stackexchange.com/questions/15729/storing-prices-in-sqlite-what-data-type-to-use

I just need a way to convert 4200 to $42.00 when I call item.price and also sanitize and convert the input into 4200.

Godwit

mongoose-currency is the solution to your problem. – Gunther

Answer 1

A bit late but...

The answer of chovy almost worked for me – I just needed to add { toJSON: { getters: true }} as an options parameter in the schema declaration.

Example:

import mongoose from 'mongoose'
const productosSchema = new mongoose.Schema(
    {
        name: String,
        price: {
            type: Number,
            get: v => (v/100).toFixed(2),
            set: v => v*100
        }
    },
    { 
        toJSON: { getters: true } //this right here
    }
);
export default mongoose.model('productos', productosSchema)

This works on Mongoose 6.0.14.

References: https://mongoosejs.com/docs/api.html#document_Document-toJSON

Erasure

Answer 2

This is what I ended up doing...

I stored price as cents in database, so it is 4999 for 49.99 as described here: https://dba.stackexchange.com/questions/15729/storing-prices-in-sqlite-what-data-type-to-use

the getPrice will convert it back to readable format, so I can use item.price in my views w/o modifying it.

the setPrice converts it to cents.

model:

var ItemSchema = new Schema({
    name            : { type: String, required: true, trim: true }
    , price             : {type: Number, get: getPrice, set: setPrice }
});

function getPrice(num){
    return (num/100).toFixed(2);
}

function setPrice(num){
    return num*100;
}

I opted to only allow digits and decimal in price field, without $. So they can enter 49, 49.99, 49.00, but not 49.0 or $49

validation using regex:

if ( req.body.price ) {
    req.assert('price', 'Enter a price (numbers only)').regex(/^\d+(\.\d{2})?$/);
}

I wish there was a way to allow the $ because I think its a usability issue, just let the user enter it, but strip it off. I'm not sure how to do that and still validate that we have a price and not a bunch of letters for example.

Godwit

I must be missing something... Surely just storing the price as a number (40.99 for example) is correct? Then, your view would display this with the $ (or £) - you could even store CurrencyCode (USD, GBP) in a separate field for this reason? – Truthful

When I researched storing price (and I remember PayPal doing this as well), they stored it in cents. I don't know the reasoning for this, but it seems to be pretty standard practice. – Godwit

I've no problem with storing it in cents, in fact that sounds like a really good idea, however storing the $ with it is just plain... wrong. Storing it separately would be fine (although I'd suggest using iso4217 currency code) - will allow you to properly sort on price that way – Truthful

what would my price definition look like? { price: 4999, code: 'USD' } – Godwit

yeah... if you want to embed a 'price' doc, alternatively, just have {_id: xxx, name: 'something', price: 4999, price_code: 'USD'} etc... – Truthful

Storing currency as a Number (which is a double internally) is problematic because floating point arithmetic is inherently imprecise. 3.3*3 becomes 9.899999999999999. 1.03+1.19 becomes 2.2199999999999998. – Maier

This method does not seem to work anymore in Mongoose 4.x. Can anyone confirm? – Hinder

@SirBenBenji Same for me, I realize this is a bit late but did you figure it out? I can't seem to get setters/getters to work at all. – Hydrogenate

Answer 3

Hint: The method described here is basically just another implementation of chovy's answer.

Workaround for Mongoose 3 & 4:

If you have trouble to define getters and setters directly in the schema, you could also use the schema.path() function to make this work:

var ItemSchema = new Schema({
  name: String,
  price: Number
});

// Getter
ItemSchema.path('price').get(function(num) {
  return (num / 100).toFixed(2);
});

// Setter
ItemSchema.path('price').set(function(num) {
  return num * 100;
});

Perishing

This is not true, it's still possible to define getters/setters directly in the schema definition: mongoosejs.com/docs/api.html#schematype_SchemaType-set – Intransigent

@Intransigent Sorry for the delay on this, you are right. I experienced issues with chovy's answer at a time where other users had also issues with this and found out this as a workaround. Tested it with 4.8.6 and it seems to work fine now with schema getters / setters. Will update the answer to clarify that. – Perishing

Answer 4

Adds schema type "Currency" to mongoose for handling money. Strips out common characters automatically (",", "$" and alphabet chars)

https://github.com/paulcsmith/mongoose-currency

What it does:

Saves a String as an integer (by stripping non digits and multiplying by 100) to prevent rounding errors when performing calculations (See gotchas for details) Strips out symbols from the beginning of strings (sometimes users include the currency symbol) Strips out commas (sometimes users add in commas or copy paste values into forms, e.g. "1,000.50) Only save from two digits past the decimal point ("$500.559" is converted to 50055 and doesn't round) Strips [a-zA-Z] from strings Pass in a string or a number. Numbers will be stored AS IS. Assumes that if you set the value to an integer you have already done the conversion (e.g. 50000 = $500.00) If a floating point number is passed in it will round it. (500.55 -> 501). Just pass in integers to be safe.

Hope it helps some1.

Derisive

Dude currency is undefined what is the problem in my case? – Refit

Answer 5

I've been researching for a while on this topic, because I want to store not only price, but version, which both may have trailing 0s that get chopped off when stored as a number. As far as I know, Mongoose/MongoDB can't save a number with trailing zeroes.

Unless you save the number as a string.

Aside from storing numbers in tens or thousands and dividing or parsing, you can also store it as a string. This means, you can always just print it out when you need to show "1.0" or "1.00" by just using the variable without any conversion. Due to JavaScript being untyped, you can still compare it to numbers (make sure it's on the left hand side). Var < 10, for example, will return the right evaluation, even when var is a string. If you're comparing two variables, you'd need to make sure that they're both numbers, though. When you need a number, you can multiply the string by one (var * 1 < var2 * 1), which will ensure that JavaScript treats the var as a number, although it will lose the trailing zeros.

On the one hand, storing it as a string means you need to do a conversion every time you want to use the variable as a number. On the other hand, you would presumably be doing a numeric conversion anyway (var / 100) every time you want to use a cents number as a dollar amount. This option would depend on how frequently you need to your value as a number. Also it may cause bigger bugs if you forget that your variable is a string than if you forget that your variable is in cents.

(However, it's a great fit for version numbers that would only ever be used for display and comparison.)

Ostraw

Answer 6

The numeral module will accomplish that: http://numeraljs.com/ https://www.npmjs.com/package/numeral

Dagan