[#680,!426] Delete embedded options when subnet gets deleted in mysql_cb.

src/share/database/scripts/mysql/dhcpdb_create.mysql

@@ -2377,6 +2377,40 @@ SET version = '8', minor = '1';
 
 # This line concludes database upgrade to version 8.1.
 
+# Do not perform cascade deletion of the data in the dhcp4_pool because
+# the cascade deletion does not execute triggers associated with the table.
+# Instead we are going to use triggers on the dhcp4_subnet table.
+ALTER TABLE dhcp4_pool
+    DROP FOREIGN KEY fk_dhcp4_pool_subnet_id;
+
+ALTER TABLE dhcp4_pool
+    ADD CONSTRAINT fk_dhcp4_pool_subnet_id FOREIGN KEY (subnet_id)
+    REFERENCES dhcp4_subnet (subnet_id)
+    ON DELETE NO ACTION ON UPDATE CASCADE;
+
+
+# Drop existing trigger on the dhcp4_subnet table.
+DROP TRIGGER dhcp4_subnet_ADEL;
+
+# Create new trigger which will delete pools associated with the subnet and
+# the options associated with the subnet.
+DELIMITER $$
+CREATE TRIGGER dhcp4_subnet_BDEL BEFORE DELETE ON dhcp4_subnet
+    FOR EACH ROW
+    BEGIN
+        CALL createAuditEntryDHCP4('dhcp4_subnet', OLD.subnet_id, "delete");
+        DELETE FROM dhcp4_pool WHERE subnet_id = OLD.subnet_id;
+        DELETE FROM dhcp4_options WHERE dhcp4_subnet_id = OLD.subnet_id;
+    END $$
+DELIMITER ;
+
+
+# Update the schema version number
+UPDATE schema_version
+SET version = '8', minor = '2';
+
+# This line concludes database upgrade to version 8.2.
+
 
 # Notes:
 #