[WIP] Fix aliased attributes sql literals

[waiting-for-dev]

References #316

This is still a WIP to fix referenced bug: tests are missing and some
previous have been broken. A more comprehensive solution needs to be
found, so I ask for any feedback or help.

When sequel creates a sql expression from an object, it tries to call
one the two following methods in this order:

• sql_literal_append
• sql_literal

rom-sql is implementing sql_literal, which only takes as argument the
sequel datastore. However, sql_literal_append takes two arguments: the
datastore and the sql string built so far.

The partial solution implemented in this commit matches the sql string
at the moment of invocation in order to detect whether we are to the
left of the FROM table clause or to the right of it. If we are to the
left we are referencing a column from the SELECT clause, so we keep
appending name AS alias. However, if we are to the right, what we need
is the canonical sql literal representation (i.e. WHERE name = 1).

This is obviously very hacky. I haven't found any way to inspect the
dataset or any other component in order to have a solid knowledge about
which sql clause is being constructed. So I'm afraid it could be the
only possible fix.

In case something in the same vein of this solution is to be
implemented, we should think the most comprehensive way to match the sql
query built so far. For example, the current solution would not work for
an UPDATE table SET name as alias = 1... statement. We should also
study whether it could break edge corner cases, like a column name
containing FROM table in its name.

[solnic]

What about handling this at relation/schema level? This would be more explicit and less risky. We can convert attributes depending on the context in which they are used (this is how it works already in the relation API).

[waiting-for-dev]

Thanks for your feedback @solnic . I didn't realize it was possible at that level. Cool, I'll dig into it and try to find something better.

[waiting-for-dev]

Not sure if it is the same issue but, for a :foo aliased attribute the following doesn't work:

relation.where { relation[:foo].like("something") }

The above fails with #like not being a method. Instead, one must do:

relation.where { relation[:foo].canonical.like("something") }

For now, I just leave a note here so I don't forget.

[waiting-for-dev]

What do you think of something like last commit, @solnic ? If it's ok, then we have to do something similar to order and any other clause where we need it.

[solnic]

@waiting-for-dev could you re-push this branch to rom-sql repo and we could take it from there?

[waiting-for-dev]

Ok. Closing in favour of #325 I cleaned the commit history there.