kql - Can't parse date from concatenated string

Question

I am about to lose my mind with something so apparently simple. I want to parse a string into a datetime but it keeps returning null.

If I do todatetime(strcat(2020,"-11-7")) it returns null. And if I do todatetime("2020-11-7") it works. I compared both strings and they are equal.

This is the code that I am testing:

let dateStr = strcat(2020,"-11-7");
let dateStr2 = "2020-11-7";
print dateStr == dateStr2 // True
print todatetime(dateStr) == todatetime(dateStr2) // False

Any idea why is this happening and how can I solve it?

question from:https://stackoverflow.com/questions/65853355/cant-parse-date-from-concatenated-string

Answer 1

Your attempt to convert strcat(2020,"-11-7") to datetime fails because the string that is created is not a supported datetime format. Please see the list of supported formats in the doc.

However, if you try to convert strcat(2020,"-11-07") (note the 07 instead of just 7), then it will produce the desired result.

Converting "2020-11-7" to datetime does work (like you noticed) even though this is not a supported format, for backward compatibility (but it's recommended to refrain from using unsupported formats, in any case).