[DataQuery] Less than with nullable date/int

[cheng93]

Description

Given the following data

[{age: 1}, {age: 2}, {age: null}]

when the oData query filter, $filter=age lt 2, is applied, you would not expect the last value to show up

Steps To Reproduce

https://stackblitz.com/edit/angular-rsabply1?file=src%2Fapp%2Fproducts.ts,src%2Fapp%2Fapp.component.ts

Set the filter to be less than today. You can see that undefined is filtered, but not null

I think it's because underneath, it's using JS default filter, i.e

[null, undefined, 1, 0].filter(x => x < 2) // [null, 1, 0]

Screenshots or video

No response

Actual Behavior

null is there

Expected Behavior

null not to be there

Browser

Chrome

Browser version

latest

OS type

Windows

OS version

No response

Last working version of the Kendo UI for Angular package (if regression).

No response

[cheng93]

Is this a feature, or is it a bug?

[georgi-sla]

Hello, @cheng93!

Indeed, you are correct that the observed behavior originates from JavaScript and is, in fact, the expected one.

Generally speaking, when performing various relational comparisons (>, <, >=, <=) between numbers, dates, and null, null is typically type coerced to 0. Consequently, null is less than positive numbers and dates(dates are converted to milliseconds for such operations), and thus, it is part of the filtered data:

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Less_than_or_equal#comparing_boolean_null_undefined_nan

On the other hand, undefined behaves slightly differently - it is coerced to NaN in such comparisons and as a result, leads to a false outcome:

• https://stackoverflow.com/questions/63203854/why-undefined-plus-undefined-equals-to-nan-in-javascript

With that being said, you could consider using the built-in isNull and isNotNull filter operators, as they would allow handling scenarios where some property of the data items is equal to null/undefined:

• https://www.telerik.com/kendo-angular-ui/components/data-query/api/filteroperator#isnull
• https://www.telerik.com/kendo-angular-ui/components/data-query/api/filteroperator#isnotnull