How to store money in elasticsearch

Question

I've created an elasticsearch index and my current mapping stores the dollar amount of an item as a string. This is proving to be difficult as I can't search/filter on this value correctly.

GET catalog/product/_search
{
  "filter": {
    "range": {
      "price": {
        "from": 230.0,
        "to": 300.0
      }
    }
  }
}

Where price is mapped as a string. I used a string because going from a python decimal value, I've had issues where this value suddenly gets values at something like 17.989999999999999999998789. This only happens sometimes but I don't wanna get into the issue of going from a python decimal to a java double/float (so I just str() the thing).

Any thoughts on a better approach? Should I bite the bullet and map the price to a double or a float?

Answer 1

This occurs because ElasticSearch has no built-in type for decimals or currency, so your value is likely being converted to a float and suffering from floating point precision issues.

You should be able to get around this by simply storing the value as a long (e.g. the number of cents rather than dollars) and converting to and from your decimal application-side.

Since you'll only ever do this conversion for values you are already enumerating, the performance impact should be negligible.

Answer 2

In newer version (checked for 5.0), probably the best option is to use scaled_float with scaling_factor = 100 like in their example:

PUT my_index
{
  "mappings": {
    "my_type": {
      "properties": {
        "number_of_bytes": {
          "type": "integer"
        },
        "time_in_seconds": {
          "type": "float"
        },
        "price": {
          "type": "scaled_float",
          "scaling_factor": 100
        }
      }
    }
  }
}

You can find their doc here.