[Flow] Best practice for Persist Value Object

[Rocky]

Hi Christian,

Thanks! Now the value objects could be persisted. 

But the problem is when remove the model, I will get SQL error saying "SQLSTATE[23000]: Integrity constraint violation: 1451 Cannot delete or update a parent row: a foreign key constraint fails (...". The reason is Doctrine will generate 2 tables. Below are the SQL:
 CREATE TABLE `hwwcn_sponsor_domain_model_abstractapplication_expenses_join` (
  `sponsor_abstractapplication` varchar(40) NOT NULL,
  `hwwcn_model_expense` varchar(40) NOT NULL,
  PRIMARY KEY (`sponsor_abstractapplication`,`hwwcn_model_expense`),
  KEY `IDX_26B5C670561DC0D6` (`sponsor_abstractapplication`),
  KEY `IDX_26B5C67058C3DB9F` (`hwwcn_model_expense`),
  CONSTRAINT `FK_26B5C67058C3DB9F` FOREIGN KEY (`hwwcn_model_expense`) REFERENCES `hwwcn_sponsor_domain_model_expense` (`persistence_object_identifier`),  
  CONSTRAINT `FK_26B5C670561DC0D6` FOREIGN KEY (`sponsor_abstractapplication`) REFERENCES `hwwcn_sponsor_domain_model_abstractapplication` (`persistence_object_identifier`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

CREATE TABLE `hwwcn_sponsor_domain_model_expense` (
  `persistence_object_identifier` varchar(40) NOT NULL,
  `item` varchar(255) NOT NULL,
  `amount` double NOT NULL,
  PRIMARY KEY (`persistence_object_identifier`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 

If I delete the foreign key part when create the join table, I could delete the expense but that will make other records in the join table refer to deleted expense which is not longer exist. Any suggestion please?