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what is the difference between owned one to many relationship and owned one to many bidirectional relationship i read the article below but i don't understand it. Article

David Underhill
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Kerem Pekçabuk
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2 Answers2

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The owned one to many bidirectional relationship just means that the children have a reference to the parent. For example, the child below can access the parent via persistentUser. If persistentUser didn't exist in the PersistentLogin class then it would not be bidirectional.

One-to-Many (PersistentUser.java - Parent):

@OneToMany(mappedBy = "persistentUser", cascade = CascadeType.ALL)
private Collection<PersistentLogin> persistentLogins;

Many-to-One (PersistentLogin.java - Child):

@ManyToOne(fetch = FetchType.LAZY)
private PersistentUser persistentUser;
Taylor Leese
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  • Hi taylor thanks for the reply. I'm new to GAE so i may understand it a little hard. Now guess there is a FootballTeam.java class and a Player.java class. A Football team have many Players. Now what happens if i do this relationship bidirectional ? – Kerem Pekçabuk Jun 07 '10 at 20:55
  • That relationship would be represented the same way as the example I gave. The @OneToMany relationship would be on the FootballTeam class with a Collection players attribute. The @ManyToOne relationship would be in the Player class with a FootballTeam team attribute. – Taylor Leese Jun 08 '10 at 00:38
  • Taylor i understood that but i think i don't know the meaning of the word bidirectional in relationships.What happens if the relation becomes bidirectional ? could you please give me an example about football team class and player class ? Thanks – Kerem Pekçabuk Jun 08 '10 at 20:46
  • The term bidirectional just means that the player has a reference to the team. If this relationship does not exist on the player then it is not bidirectional. Rather, it would be a unidirectional relationship. – Taylor Leese Jun 08 '10 at 21:47
  • An owned one to many relationship means that every record must have a referance.For example every player must have a team.It looks like the same thing in your answer. i couldn't understand the difference between an owned relationship and bidirectional relationship. – Kerem Pekçabuk Jun 10 '10 at 20:56
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Finally i understand it.Guess i have a Class Named FootBallTeam and it has a property named teamname. Now the pseudue code is

   FootBallTeam ft = new FootBallTeam();
    ft.setteamname("Barcelona");

then add 3 Player Class entity under this team named Messi,Xavi,Iniesta. now if the relationship is bidirectional when i run the code below,

   ft.setteamname("Real Madrid");

it automatically runs the below codes behind the scenes.

Messi.setteamname("Real Madrid")
Xavi.setteamname("Real Madrid")
Iniesta.setteamname("Real Madrid")
Kerem Pekçabuk
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