Support cardinality :many in MS SQL: replace array_agg with Clojure fn #17
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MS SQL does not support arrays. This patch removes array_agg and moves aggregation into Clojure code.
Imagine you have Account and Address one-to-many relation. You filter on
Account.ID and left-join Address to Account. Then not-only you filter by
Address.AccountId but moreover Account must exist.
Now is LEFT JOIN necessary? It would return result [Account.ID, NULL] if no
Address exist. But these results are filtered out in later stages of query
post-processing, because when there is no Address, adapter will return
{::account/id ID} and not {::account/id ID, ::account/addresses []}.
LEFT JOIN is not necessary.
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Does this test out against the other databases? Seems like a perfectly good idea to me, and I'm willing to merge it. I don't use this adapter, so it won't get much testing from me. |
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If you'll squash this and confirm it is tested, I'll merge and release it. |
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to-many-join-column-queryusesGROUP BYandarray_aggaggregate function. Unfortunately not all SQL databases implement it, SQL Server is one of them (#15).I propose to move this functionality out of SQL to Clojure function. Return all relations and group them in Clojure code. This makes it less dependent on specific SQL implementations. One drawback could be performance (it transfers more data) but I estimate the impact will be minimal. I guess performance is not main fulcro-rad-sql concern and its performance can be tuned elsewhere (roundtrips, formattign sqls with ids).
I considered also solution with string_agg, which strangely is implemented in MS SQL. But I decided against as primary keys can have different types and this could lead to mess.