Add random_order method to query objects

[wout]

Here's a proposal for the random_order implementation (#755).

Initially, I tried to add a :random option to Avram::OrderBy but a few things were bad about that approach:

• too many if statements to switch between order by random and order by column clauses
• unnecessary attributes for the random option
• unused column argument in the initializer, requiring the column attribute to be nilable
• clunky internal API (e.g. Avram::OrderBy.new(nil, :random))

That's why I decided to create an abstract class called Avram::OrderByClause and split out the two different order methods into two subclasses called Avram::OrderBy and Avram::OrderByRandom. The Avram::OrderBy class could have been renamed to Avram::OrderByColumn for consistency, but by keeping the old name, we're not breaking anything.

Having multiple order by classes also will make it easier to add more order methods later on. Like ordering by an array for example, which is something I've needed in the past. For example, we could also add an Avram::OrderByArray class, generating the following clause:

ORDER BY array_position('{5,1,4,3,2}'::int[], item.id::int)

Which could look like:

Avram::OrderByArray.new(:id, [5,1,4,3,2], :nulls_last)

[jwoertink]

wow! This is a lot more code than I was thinking 😂 This is pretty great though. It does feel like this will allow things to be more extensible for the future

[wout]

Yeah, I didn't expect to add this amount of code either. But you know how those things go...

[wout]

You're right, re-using the column attribute is much more elegant.

[jwoertink]

Looks good!

[wout]

Shall I update the docs as well?

[jwoertink]

We should at least open an issue to update docs. It won't go out until next release