ExpressionMethods subset for Untyped

[LucaCappelletti94]

Backend

PostgreSQL, SQLite

What do you want to add to diesel?

At this time, ExpressionMethods is not implemented for Untyped, and with good reason as several of the methods therein cannot, at least with the present trait bounds, be ever implemented for Untyped. That being said, several methods in this trait can be implemented for Untyped, and I believe they should be available as otherwise it severely limits what is filtrable in untyped dynamic selects.

Going in alphabetical order, I believe that the following should be implementable for Untyped:

• asc
• desc
• is_not_null
• is_null

For completeness sake and to avoid errors, here are the other methods which I believe cannot be implemented for Untyped:

• between
• eq
• eq_any
• ge
• gt
• le
• lt
• ne
• ne_all
• not_between

Implementation notes

Ideally, if API breaking was not an issue, I would split the methods into two traits, one for the non implementable methods and another for the methods which can be implemented, and then have the former have the latter as super-trait.

Since API breaking is a concern, for the time being I would propose to create a separate UntypedExpressionMethods trait, implement it for Untyped, and later on at the next major release we could do the trait mitosis described above.

Additional details

No response

Checklist

• I have already looked over the issue tracker and the discussion forum for similar possible closed issues.

[LucaCappelletti94]

Closing as completed with PR #4930