Commits on Apr 22, 2023

1. m2m relations - do not use subquery when not necessary …

   1. performance optimization for operations on m2m relations
   `ManyToManyModifyMixin` creates a subquery and moves all filters from the main query into it.
   > This is done so that we are able to `innerJoin` the join table to the query. Most SQL engines don't allow joins in updates or deletes. Join table is joined so that queries can reference the join table columns.
   
   But, the subquery is not really needed in all types of operations
   - e.g. a query with just a findById(s) operation - usually coming from graph upsert
   - or when query builder is not operating on the join table but e.g. the target related table
   
   2. Additionally, for mysql:
   
   - extract the subquery selecting related ids to separate query run before the main query
   to avoid `ER_CANT_UPDATE_USED_TABLE_IN_SF_OR_TRG` mysql error
   when executing a db trigger on a join table which updates related table
   
   This workaround is only needed for MySQL.
   It could possibly be applied to all DBMS, if proven necessary,
   but others seem to handle such cases just fine.
   
   https://stackoverflow.com/a/2314264/3729316
   > MySQL triggers can't manipulate the table they are assigned to. All other major DBMS support this feature so hopefully MySQL will add this support soon.
   > ~ Cory House, 2010

   

   marcinlee authored and falkenhawk committed Apr 22, 2023
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