Only INSERT if reservation doesn't exist yet.

Hey guys, I am doing a policy to prevent a user from "double" booking a listing, and I am wondering if the following WITH CHECK is valid or if it's efficient.

Conditions = Check if the authenticated user

reserved_by

reserved_by

already booked the existing

listing_id

listing_id

WITH CHECK (auth.uid() = reserved_by 
AND NOT EXISTS 
    ( select 1 from reservations where       
listing_created_by = listing_created_by));

WITH CHECK (auth.uid() = reserved_by 
AND NOT EXISTS 
    ( select 1 from reservations where       
listing_created_by = listing_created_by));

Only INSERT if reservation doesn't exist yet.

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Only INSERT if reservation doesn't exist yet.

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