Schema::table('tbl_notifications', function(Blueprint $table) {
            $table->foreign('severity_id', 'fk_severity_id')->references('id')->on('tbl_notification_severity')->onUpdate('NO ACTION')->onDelete('CASCADE');
            $table->foreign('category_id', 'fk_not_category_id')->references('id')->on('tbl_notification_categories')->onUpdate('NO ACTION')->onDelete('CASCADE');
            $table->foreign('type_id', 'fk_not_type_id')->references('id')->on('tbl_notification_types')->onUpdate('NO ACTION')->onDelete('CASCADE');
        });