JPA - Persisting a One to Many relationship

Question

Maybe this is a stupid question but it s bugging me   I have a bi-directional one to many relationship of Employee to Vehicles  When I persist an Employee in the database for the first time  i e  it has no assigned ID  I also want its associated Vehicles to be persisted    This works fine for me at the moment  except that my saved Vehicle entity is not getting the associated Employee mapped automatically  and in the database the employee id foreign key column in the Vehicle table is null   My question is  is it possible to have the Vehicle s employee persisted at the same time the Employee itself is being persisted  I realise that the Employee would need to be saved first  then the Vehicle saved afterwards  Can JPA do this automatically for me  Or do I have to do something like the following   Vehicle vehicle1   new Vehicle    Set lt Vehicle gt  vehicles   new HashSet lt Vehicle gt     vehicles add vehicle1    Employee newEmployee   new Employee  matt    newEmployee setVehicles vehicles   Employee savedEmployee   employeeDao persistOrMerge newEmployee    vehicle1 setAssociatedEmployee savedEmployee   vehicleDao persistOrMerge vehicle1     Thanks   Edit  As requested  here s my mappings  without all the other methods etc     Entity public class Employee        Id      GeneratedValue strategy   GenerationType AUTO       Column name  employee id       private Long id        OneToMany mappedBy  associatedEmployee   cascade CascadeType ALL      private Set lt Vehicle gt  vehicles                Entity  public class Vehicle        Id      GeneratedValue strategy   GenerationType AUTO       Column name  vehicle id       private Long id        ManyToOne      JoinColumn name  employee id       private Employee associatedEmployee               I just realised I should have had the following method defined on my Employee class   public void addVehicle Vehicle vehicle        vehicle setAssociatedEmployee this       vehicles add vehicle       Now the code above will look like this   Vehicle vehicle1   new Vehicle     Employee newEmployee   new Employee  matt    newEmployee addVehicle vehicle1   Employee savedEmployee   employeeDao persistOrMerge newEmployee     Much simpler and cleaner  Thanks for your help everyone

User · Answer

One way to do that is to set the cascade option on you "One" side of relationship:

class Employee {
   // 

   @OneToMany(cascade = {CascadeType.PERSIST})
   private Set<Vehicles> vehicles = new HashSet<Vehicles>();

   //
}

by this, when you call

Employee savedEmployee = employeeDao.persistOrMerge(newEmployee);

it will save the vehicles too.

User · Answer

You have to set the associatedEmployee on the Vehicle before persisting the Employee   Employee newEmployee   new Employee  matt    vehicle1 setAssociatedEmployee newEmployee   vehicles add vehicle1    newEmployee setVehicles vehicles    Employee savedEmployee   employeeDao persistOrMerge newEmployee

[java] JPA - Persisting a One to Many relationship

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