Properly qualify relations when in Relation#union #334
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flash-gordon
approved these changes
May 15, 2019
| opts = { alias: alias_name.to_sym, **options } | ||
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| new_schema = schema.qualified(opts[:alias]) | ||
| new_schema.(new(dataset.__send__(__method__, relation.dataset, opts, &block))) |
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new(dataset.__send__(__method__, relation.dataset, opts, &block), schema: new_schema)would be better here
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| it 'qualifies the table as the concatenated relation names' do | ||
| result = relation1.union(relation2) | ||
| expect_to_have_qualified_name(result, :users__tasks) |
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I'm not sure if we even need to test this but anyway
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Good catch |
dgollahon
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Jun 3, 2023
- When merging relations with virtual columns the qualified projection (added in rom-rb#334) causes the virtual column to be moved into the outer select. This means that column will always be hardcoded to `NULL` instead of selecting from the result of the union. This is a [not-that-esoteric technique with unions](https://stackoverflow.com/a/39766372). This also worked in ROM prior to rom-rb#334. This PR is really an issue/bug report just in the form of a failing test. I don't have a good idea as to what the right solutin is but I figured it would be helpful to at least have a very concrete demonstration of the issue.
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When Sequel performs a union of two datasets, it will alias the resulting union as
t1by default. As a result,select_appendanything that required a qualified column will not work after performing a union.To fix this, this PR ensures we qualify the schema when performing a union. If relation_a and relation_b are of the
Relation::Name, then we use that name as the alias. If they are different, we default the alias to#{relation_a.name}__#{relation_b.name}. This is not technically required, but IMO makes the relation more easily inspectable/debuggable, and is more resistant to cases when user's manually qualify columns.