![]() ![]() Postgres Trigger Example 2: Creating an Audit Table.Postgres Trigger Example 1: Creating a Time Clock.This article contains all the information I wish I could have shared with my brother on how to effectively use SQL triggers. When building highly data oriented software, especially when the data is of financial nature and accuracy is of high demand, you're more likely to see data being manipulated at a lower level, in a more direct way. During my time working on custom ERP-like software, SQL triggers were an invaluable tool. In the world of open source start-up style full-stack development (think Django, Rails, Javascript, PHP, MySQL, Postgres.), ORMs are very popular and features like SQL triggers are far less conventional.īut there is still value with SQL triggers. With my only programming experience being recreating my favorite video game in VB6, I had little consolation to offer.įast forward 16 years, and now I can see from my brother’s perspective. Jonathan came home one day frustrated by a database full of convoluted SQL triggers. My brother, Jonathan, had just begun his software career at a startup. And there are various other advantages - like you have the default email in the main table without join.I was 12 years old when I first heard about SQL triggers. , UNIQUE (organization_id, email) - seems redundant, but required for FKĪDD CONSTRAINT company_addressesn_default_email_fkeyįOREIGN KEY (organization_id, email) REFERENCES email (organization_id, email) , organization_id int NOT NULL REFERENCES company_addresses ON DELETE CASCADE , email text UNIQUE - FK added below - can also be NOT NULL Organization_id integer GENERATED ALWAYS AS IDENTITY PRIMARY KEY It's inefficient to update other rows to mark a new one as "default".Ĭonsider to add am email column for each organization that holds (and points to) the "default" instead: CREATE TABLE company_addresses ( ![]() That said, I suggest a completely different approach: Alternative db design INSERT INTO company_addresses(organization_id, is_default) VALUES (2, true) Alternative with CTE and no trigger WITH pre_emptive AS ( Is_default = true is just a noisy way of saying is_default. Typically, it's cleaner to just write separate trigger functions and triggers for INSERT and UPDATE (unless this leads to massive code duplication).įor dynamic SQL, pass the value OLD.organization_id as value.īut why dynamic SQL in the first place? I made it static. (Postgres is free to evaluate expressions in arbitrary sequence.) I hid that in a nested IF statement. It's not safe to reference OLD in the INSERT case on the outer level. Use instead: CREATE OR REPLACE FUNCTION public.ensure_only_one_default_address()ĪND organization_id = NEW.organization_id - !!! NEW, not OLD Goes to show the importance of declaring the Postgres version in use. Previously, references to these variables could be parsed but not In PL/pgSQL trigger functions, the OLD and NEW variables now read as This used to raise and exception immediately in older Postgres versions. organization_id instead of NEW.organization_id in the UPDATE - which is bound to do nothing in the INSERT case, where OLD is not defined. I though that the trigger would fire first, then the unique constraint. The constraint error is happening because I have a unique partial index on (organization_id, is_default) WHERE is_default = true, but I though that the trigger would fire first, then the unique constraint so I'm wondering if there is anything in the internals of Postgres that I'm missing. IF (TG_OP = 'UPDATE' AND OLD.is_default = true) THENĮXECUTE format('UPDATE %I.%I SET is_default = false WHERE is_default = true AND organization_id = %L ', TG_TABLE_SCHEMA, TG_TABLE_NAME, OLD.organization_id) ĬREATE TRIGGER ensure_only_one_default_addressīEFORE INSERT OR UPDATE OF is_default ON pany_addressesįOR EACH ROW WHEN (NEW.is_default = true)ĮXECUTE PROCEDURE public.ensure_only_one_default_address() nothing to do if updating the row currently enabled This is what I have: CREATE OR REPLACE FUNCTION public.ensure_only_one_default_address() The update part is working, however I'm getting a unique constraint error for insert. I'm trying to create a trigger where if the is_default column is set to true on an insert or update, it sets the rest of the rows to false and the current one to true. In my database schema an organization can have multiple addresses but only one default address. ![]()
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