Floating-point types are not always serialized with a decimal point

[Alkaersig]

Elastic.Clients.Elasticsearch version:
8.0.2

Elasticsearch version:
8.5.0

.NET runtime version:
6.0

Operating system version:
Windows 11

Description of the problem including expected versus actual behavior:
Ran into another problem while migrating one of our smaller projects to v8. Trying to index a range of documents i got an error that [float] could not be converted to [long]. Inspecting the request, it turns out that whenever a floating-point value does not have a decimal part, it is serialized as an int (without a decimal point/radix).

I guess this problem was introduced by the new Serializer in the v8 client. This was fixed some years ago back in v7:
#3657

Steps to reproduce:
1: Create a simple document

public class FloatDocument
{
  public decimal Amount { get; set; }
}

2: Insert a range of documents with a mix of integers and decimal numbers:

var data = new List<FloatDocument>();
data.Add(new FloatDocument() { Amount = 11 });
data.Add(new FloatDocument() { Amount = 1.15M });
data.Add(new FloatDocument() { Amount = 3.76M });

await esClient.IndexManyAsync<FloatDocument>(data, "index");

3: Returns an error: mapper [amount] cannot be changed from type [float] to [long]" since it serializes to:

[{
  Amount: 11
},
{
  Amount: 1.15
},
{
  Amount: 3.76
}]

Expected behavior
Floating-point types should always be serialized as floating-point types (serialized with a decimal point).

[stevejgordon]

Thanks for raising this, @Alkaersig. I certainly see the problem this can introduce. We'll need to consider introducing custom converters to work around the choices made in System.Text.Json for such numbers. A workaround, for now, is to explicitly map fields in advance for the expected number type.

[Alkaersig]

Hi @stevejgordon

Thanks for coming back on this. I already attempted the workaround, mapping our decimals to float using a template that creates the mapping when the index is created, but when trying to index a decimal that has no decimal value (like 10 (10.0)) , we still get the error (a [long] cannot be mapped to a [float]).

So i guess there is more to this, since i would expect it to map just fine to a float, even though ES parses it as a long (well at least if the long-value is not bigger than the max value of a float).

[stevejgordon]

Oh, that's interesting. I thought I'd previously tested that without an issue. I'll take a look, and we'll find a solution.

[Alkaersig]

Hi @stevejgordon

Just a little Christmas update.

We actually got it working now after updating from RC2 to 8.0.2 and mapping the field to float manually using index_templates. So the workaround do work after all.

So the issue only arises using auto-field-mapping when a long-value is encountered before a float (thus the field is mapped as long) which obviously does not support float-values :)

I updated the bug-report to reflect this (the example now has a long value in the first object while the following objects holds a float-value).

[stevejgordon]

Thanks for the update, @Alkaersig. That's good to know. It would also be possible to define your own custom System.Text.Json converter to assign to your properties to control their serialization.