[feature] Page through accounts as moderator

[tsmethurst]

Description

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This pull request implements paging through accounts alphabetically via the admin API, as opposed to paging by creation date. To accomplish this, a new index is added on a concatenation of [domain]/@[username].

Paging is also implemented in the frontend, so admins can page up and down through accounts in the settings panel.

Checklist

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• I/we have read the GoToSocial contribution guidelines.
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• I/we have commented the added code, particularly in hard-to-understand areas.
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• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
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[NyaaaWhatsUpDoc]

how come we need this second argument? i thought we were only selecting the one column here 🤔

[tsmethurst]

We are selecting account_id but also selecting domain_username as part of that query, and unfortunately bun doesn't really know what to do if you don't provide a second array to soak up the domain_username values, unless there's a way around it I haven't spotted.

[NyaaaWhatsUpDoc]

i'm wondering whether using a generated column that you also create an index on might work out a bit better (e.g. https://www.sqlite.org/gencol.html)

so generate a column name domain_username and then in both the sqlite and postgres queries can just do SELECT id FROM accounts WHERE (...) ORDER domain_username ASC/DESC. it's a column that would probably come in handy in other areas too i'm sure 🤔

[tsmethurst]

Hmm just gotta make a few fixes for postgres before squerging this.

[NyaaaWhatsUpDoc]

passing in this subquery multiple times in postgres, does it calculate it each and every time? or is it possible to use a temporary variable for it or something?

[tsmethurst]

As far as I can tell, it's computed only once because of the expression index I also added:

Index expressions are relatively expensive to maintain, because the derived expression(s) must be computed for each row insertion and non-HOT update. However, the index expressions are not recomputed during an indexed search, since they are already stored in the index. In both examples above, the system sees the query as just WHERE indexedcolumn = 'constant' and so the speed of the search is equivalent to any other simple index query. Thus, indexes on expressions are useful when retrieval speed is more important than insertion and update speed.

-- https://www.postgresql.org/docs/current/indexes-expressional.html

So I think we should be fine. I tried doing this a few different ways (using WITH, or as subqueries), but Postgres doesn't offer the same flexibility SQLite does, so this ended up being (I think) the best way of doing it, even though the queries themselves end up looking a bit silly because of the expression re-use.