Sing's Log

Triggers in PostgreSQL provide a powerful mechanism to automate tasks within the database. Let’s explore how to use triggers to automate common tasks.

1. Automatically Copying User Data to Orders

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CREATE OR REPLACE FUNCTION copy_user_data_to_order()
RETURNS TRIGGER AS $
BEGIN
    -- Concatenate user data into a string
    SELECT u.firstname || ' ' || u.lastname || ', ' || u.email
    INTO NEW.user
    FROM users u
    WHERE u.id = NEW.user_id;

    RETURN NEW;
END;
$ LANGUAGE plpgsql;

CREATE TRIGGER insert_order_trigger
BEFORE INSERT OR UPDATE ON public.orders
FOR EACH ROW
EXECUTE FUNCTION copy_user_data_to_order();

Whenever a new order is inserted or updated in the orders table, this trigger function automatically fetches the corresponding user data and stores it as a concatenated string in the user column of the order.

2. Updating Timestamp on Record Modification

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CREATE OR REPLACE FUNCTION public.update_timestamp()
 RETURNS trigger
 LANGUAGE plpgsql
AS $function$
BEGIN
    NEW.updated := NOW();
    RETURN NEW;
END;
$function$

This trigger function updates the updated timestamp column of a record with the current timestamp whenever the record is modified.

3. Using INSTEAD OF Trigger on a View

Want to update the underlying tables by View? Use the INSTEAD OF trigger

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CREATE OR REPLACE FUNCTION update_order_user_view()
RETURNS TRIGGER AS $
BEGIN
    -- Update the underlying tables as needed
    UPDATE orders
    SET paid = NEW.paid,
        register_success = NEW.register_success,
        enable = NEW.enable
    WHERE order_id = NEW.order_id;

    RETURN NEW;
END;
$ LANGUAGE plpgsql;

CREATE TRIGGER update_order_user_trigger
INSTEAD OF UPDATE ON order_user_view
FOR EACH ROW
EXECUTE FUNCTION update_order_user_view();

This INSTEAD OF trigger intercepts UPDATE operations on the order_user_view and updates the corresponding rows in the orders table based on the new values in the view.

Triggers in PostgreSQL allow for automation of repetitive tasks, enhancing the functionality and efficiency of your database.

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