**Backport:** https://codeberg.org/forgejo/forgejo/pulls/11999
`DefaultMaxInSize` is an internal parameter for limiting the size of `field IN (...)` clauses in DB queries, which is a reasonable thing to do -- in addition to the errors noted when [originally introduced](https://github.com/go-gitea/gitea/pull/4594), there are technical limits that apply to each of PostgreSQL, MySQL, and SQLite which would prevent an unbounded size for a query like this. However: the size is incredibly small at 50, and, the implementation of `DefaultMaxInSize` is really wasteful with copy-and-paste coding.
This PR:
- introduces `GetByIDs` which fetches a `map[int64]*Model` from the database for an array of ID values, while respecting `IN` clause size limits
- introduces `GetByFieldIn` which fetches a `map[int64][]*Model` from the database for an array of field values, while respecting `IN` clause size limits
- uses `slices.Chunk` for other locations where queries are too complex for these implementations
- bumps the `DefaultMaxInSize` parameter from 50 to 500, a conservative increase well under known limits, but 10x the current value:
- PostgreSQL supports up to 1GB query text size with 65,535 parameters, but I've experienced performance degradation at high value counts
- MySQL supports 64MB query text size without known limits of parameter count
- SQLite supports 32,766 parameters in a query
## Checklist
The [contributor guide](https://forgejo.org/docs/next/contributor/) contains information that will be helpful to first time contributors. All work and communication must conform to Forgejo's [AI Agreement](https://codeberg.org/forgejo/governance/src/branch/main/AIAgreement.md). There also are a few [conditions for merging Pull Requests in Forgejo repositories](https://codeberg.org/forgejo/governance/src/branch/main/PullRequestsAgreement.md). You are also welcome to join the [Forgejo development chatroom](https://matrix.to/#/#forgejo-development:matrix.org).
### Tests for Go changes
- I added test coverage for Go changes...
- [x] in their respective `*_test.go` for unit tests.
- Refactored functions are assumed to be covered by existing tests to some extent; that assumption is probably wrong but the changes here are relatively easily reviewed for correctness as well.
- [ ] in the `tests/integration` directory if it involves interactions with a live Forgejo server.
- I ran...
- [x] `make pr-go` before pushing
### Documentation
- [ ] I created a pull request [to the documentation](https://codeberg.org/forgejo/docs) to explain to Forgejo users how to use this change.
- [x] I did not document these changes and I do not expect someone else to do it.
### Release notes
- [ ] This change will be noticed by a Forgejo user or admin (feature, bug fix, performance, etc.). I suggest to include a release note for this change.
- [x] This change is not visible to a Forgejo user or admin (refactor, dependency upgrade, etc.). I think there is no need to add a release note for this change.
Co-authored-by: Mathieu Fenniak <mathieu@fenniak.net>
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/12000
Reviewed-by: Mathieu Fenniak <mfenniak@noreply.codeberg.org>
Co-authored-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
Co-committed-by: forgejo-backport-action <forgejo-backport-action@noreply.codeberg.org>
1176b58f28