MongoDB floating point value precision?

Question

As I know, JavaScript uses IEEE 754 Floating point to treat real numbers. The problem arises when using it, it's quite common issue:

0.1 + 0.2 = 0.30000000000000004

Most of time, using the module like 'big.js', but the problem is when using MongoDB.

Look at this document:

{ "_id" : ObjectId("58ff8f721bbfbcd140e472b3"), "value" : 0.1 }

When I run $inc like this:

db.dec.update({ _id: ObjectId('58ff8f721bbfbcd140e472b3') }, { $inc: { value: 0.2 }});

The result is not good at all:

{ "_id" : ObjectId("58ff8f721bbfbcd140e472b3"), "value" : 0.30000000000000004 }

I know why it's happening, but is there a way to avoid this problem?

To me this sounds like a matter of formatting, not a problem with the numeric system. Check this: var nr = .1 + .2; console.log(nr, nr.toLocaleString("en", {style: "currency", currency: "USD"})) Number#toLocaleString() — Thomas
the only point where these floating point errors actually are a problem, is when checking for equality (.1 + .2) === .3 — Thomas
@Thomas Okay, then how to use it in MongoDB query? Now I know what you are trying to say, but how put them in the query? — modernator

Max Paymar Max Paymar · Accepted Answer · 2017-04-25T19:06:22

If you know exactly the number of decimal places you want, you can do Number((.1+.2).toFixed(1)). Or you could use an orm for mongodb like mongoose, and define models for your database documents, and define the precision you want with some code in your model.

MongoDB floating point value precision?

1 Answers