Rails - upsert no unique index found

This is my migration file.

```
def change
add_index :book_owners, [:book_id, :book_detail_id], unique: true, where: 'book_id IS NOT NULL and book_detail_id IS NOT NULL'
end
```

This is my code.

```
BookOwners.upsert({
book_id: 123,
book_detail_id: 234,
...
}, unique_by: { columns: [:book_id, :book_detail_id] })
```

But I am getting this error.

`No unique index found for {:columns=>[:book_id, :book_detail_id]}`

Start by reproducing the reported migration and BookOwners.upsert call, then trace how unique_by columns are matched against the unique index. Confirm whether the partial unique index is recognized and capture the expected behavior or a clear compatibility limitation in a regression test or issue resolution.

Written by the indexing model from the issue text.