activerecord: Extract primary key constraints hash to a method #41427
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jarthorn
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Feb 12, 2021
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There is one more reference in update_columns that can use the same hash: https://github.com/rails/rails/blob/main/activerecord/lib/active_record/persistence.rb#L697
Since this hash will need to change in the future to support composite primary keys.
dylanahsmith
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cc @rafaelfranca
Extract the primary key constraints hash, used for the WHERE scope to update or delete a record, into a method. This is just a small step towards supporting a composite primary key, where we would want constraints on all primary key columns.
Context
We have a use case for using a composite primary key for performance reasons, which isn't actually supported in rails at the moment. Specifically, we use a parent record id along with the actual id to keep the associated records together for efficient querying (e.g.
(parent_id, id)).We can use
self.primary_key = :idin the model to make most things work, along with a secondary(id)index. However, that will end up taking gap locks in the innodb mysql engine when there is only an equality constraint onid, causing unnecessary lock contention.