Draft: Remove redundant foreign key on members namespace_id

What does this MR do and why?

Remove redundant foreign key on members namespace_id

Related to #377433 (closed)

Reason: check_508774aac0 actually bans NULL on member_namespace_id and fk_aa82dcc1c6 wants to set it null in contrary.

fk_aa82dcc1c6 was there and in late Sept'22 !93240 (merged) has been merged with check_508774aac0 and fk_2f85abf8f1 which deletes the row. fk_2f85abf8f1 came later, and it deletes the row before fk_aa82dcc1c6 can attempt to set it to null.

\d+ members
Check constraints:
    "check_508774aac0" CHECK (member_namespace_id IS NOT NULL) NOT VALID
Foreign-key constraints:
    "fk_2f85abf8f1" FOREIGN KEY (member_namespace_id) REFERENCES namespaces(id) ON DELETE CASCADE NOT VALID
    "fk_aa82dcc1c6" FOREIGN KEY (member_namespace_id) REFERENCES namespaces(id) ON DELETE SET NULL

Output

 bin/rails db:migrate:up:main VERSION=20221011162354
main: == 20221011162354 MembersRemoveMemberNamespaceIdForeignKey: migrating =========
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("LOCK TABLE namespaces, members IN ACCESS EXCLUSIVE MODE")
main:    -> 0.0004s
main: -- foreign_keys(:members)
main:    -> 0.0027s
main: -- remove_foreign_key(:members, :namespaces, {:column=>:member_namespace_id, :name=>"fk_aa82dcc1c6"})
main:    -> 0.0041s
main: == 20221011162354 MembersRemoveMemberNamespaceIdForeignKey: migrated (0.0120s) 

aakgun@sayglubu:~/aakgun/1/gdk/gitlab$ bin/rails db:migrate:down:main VERSION=20221011162354
main: == 20221011162354 MembersRemoveMemberNamespaceIdForeignKey: reverting =========
main: -- transaction_open?()
main:    -> 0.0000s
main: -- foreign_keys(:members)
main:    -> 0.0033s
main: -- transaction_open?()
main:    -> 0.0000s
main: -- execute("LOCK TABLE namespaces, members IN SHARE ROW EXCLUSIVE MODE")
main:    -> 0.0004s
main: -- execute("ALTER TABLE members\nADD CONSTRAINT fk_aa82dcc1c6\nFOREIGN KEY (member_namespace_id)\nREFERENCES namespaces (id)\nON DELETE SET NULL\nNOT VALID;\n")
main:    -> 0.0016s
main: -- execute("SET statement_timeout TO 0")
main:    -> 0.0003s
main: -- execute("ALTER TABLE members VALIDATE CONSTRAINT fk_aa82dcc1c6;")
main:    -> 0.0015s
main: -- execute("RESET statement_timeout")
main:    -> 0.0003s
main: == 20221011162354 MembersRemoveMemberNamespaceIdForeignKey: reverted (0.0118s) 

How to set up and validate locally

• bin/rails db:migrate:up:main VERSION=20221011162354
• bin/rails db:migrate:down:main VERSION=20221011162354

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.