删除父行中的grails外键错误

我有以下情况:

class Receipt {

   BigDecimal totalAmount;
   Date releaseDate;

   @NotNull
   Integer vatPercentage;

   @NotNull
   Integer discount;

   Boolean isPayed;
   Boolean isInvoice;
   Boolean hasStampDuty;

   Integer documentNumber;

   @NotNull
   static belongsTo = [patient:Patient, doctor:Doctor]

   @NotNull
   static hasMany = [healthServices:Receipt_HealthService]


    static constraints = {
        healthServices(blank:  false)
        patient(blank: false)
        totalAmount(blank: false, )
        vatPercentage(blank: false, nullable: false)

    }


}


class HealthService {

   int vat;
   String description;
   BigDecimal price;

   static belongsTo = [healthServiceType:HealthServiceType, doctor:Doctor]

   static constraints = {
      healthServiceType(blank: false)
      vat(size: 11..11)
      description(maxSize: 255)

    }
}  


class Receipt_HealthService {

   Receipt receipt
   HealthService healthService
   int quantity = 1

   static constraints = {
   }
}

我已经手动创建了Receipt_HealthService域类,如文章所述 here . 一切正常,但当我尝试删除Receipt实例时,我看到以下错误:

Cannot delete or update a parent row: a foreign key constraint fails
(`my_localdb`.`receipt_health_service`, CONSTRAINT 
`FK96DE98B9D3292D2C` FOREIGN KEY (`receipt_id`) REFERENCES `receipt`(`id`))

为什么会发生这种情况?为什么Receipt_HealthService实例不会自动删除?我需要更改什么才能允许自动删除并删除错误?