Don't call `#uniq` on a relation

When there was no project, no search, and no current user or author param, the AutocompleteController would call #uniq! on a relation instead of an array. This performed the less-efficient SELECT DISTINCT when it wasn't even needed (because the query wouldn't return duplicates anyway - duplicates were only added by putting a user on top of the list).

Makes the worst case for https://gitlab.com/gitlab-org/gitlab-ce/issues/27085 better.

Makes sense, thanks @smcgivern!

enabled an automatic merge when the pipeline for 17abc148 succeeds

restored source branch speed-up-members-dropdown

enabled an automatic merge when the pipeline for 17abc148 succeeds

mentioned in issue #27147 (closed)

@smcgivern Since the goal of the uniq seems to be to make sure current_user doesn't occur twice, how explicitly removing current_user from @users? Two options:

# 1
@users = [current_user, *@users.delete(current_user)]

# 2

@users = @users.where.not(id: current_user.id)
@users = [current_user, *@users]

I prefer 2, since 1, could have us end up showing an inconsistent number of users depending on whether current_user occurs on the first page.

I don't have a problem with either, but showing an inconsistent number of users has been happening for over a year

Also, for option 2, that's trickier when we're passing an author_id, because if that user ID doesn't exist, we want 20 'other' users, and if that user ID does exist, we want 19 'other' users. We could add CASE WHEN id = :author_id THEN 0 ELSE 1 AS order, and then ORDER BY order, name, but realistically I have no problem with doing this in Ruby to avoid the SELECT DISTINCT

@smcgivern I don't care all too much about the number of users, but if we can skip a uniq when we know exactly which element we want to remove, I think we should!

I've done this for the current_user case. For the author_id case, because you can pass current_user and author_id, I don't think we should do this, as we wouldn't have a relation. I'm pretty sure that we don't do that, but this isn't very well-specified, and all I really want to do here is fix that one query.

This fails in EE on the mirror page, because @users is an array at this point

https://gitlab.com/gitlab-org/gitlab-ce/issues/29316

assigned to @smcgivern

canceled the automatic merge

assigned to @DouweM

assigned to @smcgivern

assigned to @DouweM

added 1 commit

• 2c40a012 - Don't call #uniq on a relation

Compare with previous version

enabled an automatic merge when the pipeline for 2c40a012 succeeds

merged

mentioned in commit 916fae3a

mentioned in issue #27400 (closed)

Picked into 8-16-stable, will be in 8.16.3

removed ~149423 label