MYSQL and PHP: How to add mysql constraint but proceed anyway if not found

Question

I have a code where I need a foreign key check disabled when updating. But I still need it to check for the foreign key but proceed anyways if the key is not found. The installation keeps breaking due to this.

$installthis->run("
    ALTER TABLE `{$this->getTable('sweets/results')}`
      ADD CONSTRAINT `FK_SWEETS_RESULTS_SWEET_ID_SWEETS_ID` FOREIGN KEY (`sweet_id`)
      REFERENCES `{$this->getTable('sweets/sweets')}` (`id`)
        ON DELETE CASCADE
        ON UPDATE CASCADE;
    ALTER TABLE `{$this->getTable('sweets/results_values')}`
      ADD CONSTRAINT `FK_SWEETS_RESULTS_VALUES_RESULT_ID_SWEETS_RESULTS_ID` FOREIGN KEY (`result_id`)
      REFERENCES `{$this->getTable('sweets/results')}` (`id`)
        ON DELETE CASCADE
        ON UPDATE CASCADE;
");

What do I need to change or add if I want it to proceed?

Edit: The error states that

SQLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (sweets_database.sweets_results, CONSTRAINT FK_SWEETS_RESULTS_SWEET_ID_SWEETS_ID FOREIGN KEY (sweet_id) REFERENCES sweets (id) ON DELETE CASCADE ON UPDATE CASCADE), query was: INSERT INTO sweets_results (customer_id, created_time, update_time) VALUES (?, '2018-11-02 05:35:24', '2018-11-02 05:35:24')