Question

I have a table:

CREATE TABLE photo (
    photo_id BIGINT NOT NULL AUTO_INCREMENT,
    property_id BIGINT NOT NULL,
    filename VARCHAR (50) NOT NULL;
    ...
    PRIMARY KEY (photo_id),
    CONSTRAINT photo_fk_property FOREIGN KEY (property_id)
        REFERENCES property (property_id)
        ON DELETE CASCADE
);

When a row from this table is deleted, the file that is referenced by it should be deleted as well. There are two scenarios when records are deleted from this table:

1. User deletes one particular photo.
2. User deletes one particular property object (as in “real estate property”), and all the photos referencing that property are deleted automatically by ON DELETE CASCADE.

I know I can select all the referenced photos in the database before deleting a property and delete them along with their files one by one, but I’m looking for an alternate solution. Is it possible to catch the moment when a record in the photo table is deleted and delete the file automatically, without resigning the CASCADE clause, maybe in a trigger somehow?

Answer 1

You are looking for a DELETE TRIGGER. See here for a similar Problem & Solution. External action can be achieved via installation of sys_exec.

CREATE TRIGGER foobar
AFTER DELETE ON photo
FOR EACH ROW
BEGIN
   CALL sys_exec(concat('/bin/rm -f ',filename));
END