The Double-Booking This Schema Is Built to Allow
Ask anyone who knows PostgreSQL how to stop two clients booking the same specialist at the same time, and the answer comes fast: an EXCLUDE constraint with btree_gist , one && on a tstzrange , done at the database level, no application code to trust. It’s the right answer to the question most people are asking. It’s the wrong answer to the one KRI , the booking SaaS I designed and built for…
When planning appointments for beauty professionals using a PostgreSQL database, it is crucial to prevent double bookings. The most common solution is to use an EXCLUDE constraint with btree_gist, specifying && on a tstzrange. This approach is effective at the database level, eliminating the need for additional application code.
However, the booking SaaS KRI designed for beauty businesses requires a different rule. The business needs to ensure that a client's booking does not overlap any live booking for that specialist, whether it originated from a client or the owner. This order-dependent rule cannot be satisfied by a simple UNIQUE or EXCLUDE constraint over the booking intervals.
Instead, KRI implements the client-facing guard within an application transaction. A database routine or trigger with appropriate locking could also be an alternative design, but using the application path consistently is essential.
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