Translate DateOnly.DayNumber subtraction

[iPilot]

Introduction

Well, it's pretty weird example, but whatever. As soon as there is a translation DateOnly to date type it could be useful to allow to translate DateOnly.DayNumber - DateOnly.DayNumber to date - date. Luckily, both operations return integer number as a result.

Pros

• Return the difference between two DateOnly columns directly from database
• Align the translation behavior with DateTime - DateTime and DateTimeOffset - DateTimeOffset
• Allow ordering by the substruction result directly by the database engine

Cons

Unfortunately, DateOnly type itself does not support a substruction operator, only using DayNumber property and code written in a such way looks a little bit clunky and unobvious. Considering this, the translation could be implemented as an extension for EF.DbFunctions class.

[roji]

Thanks for the suggestion - I've implemented this for 9.0, along with some other translations around DateOnly.DayNumber (see #3333).