My mapping is unidirectional, not bidirectional, and would probably cause problems because neither end is marked as insertable/updatable false.

Makes me think I should write an entry about unidirectional/bidirectional and all the gotchas.

Thanks for pointing this out!

@OneToMany(
mappedBy = “item”, cascade=CascadeType.ALL)
@OrderBy(“userId,date,amount”)
public List getBids() {
return bids;
}
and at the Bids class

@ManyToOne( targetEntity = com.stevideter.domain.Item.class )
@JoinColumn(name = “itemid”, nullable = false)
public Item getItem() {
return item;
}

your comment:
If we annotate the Bids in Item with mappedBy, we’re also telling Item how it relates to Bids, but with an important caveat — we’re telling Item it is not responsible for managing that relationship.

I really dont think this is what we are telling the hibernate when we use the mappedBy attribute as

the mappedBy=”item” is pointing to the item and does it not mean that it is the item at the Bids class responsible for the relationship.

By using mappedBy attribute we are making the Item and the Bids class to be bidirectional and if we don’t have the mappedBy attribute would it not be treated as unidirectional.

In your ManyToOne mapping in the Bids class, You have defined that itemid is the foreign key and what is the need to say the same thing in your OneToMany mapping aswell.
Please do clarify and if i am missing some important point you were trying to highlight to me, do accept my ignorance.

The JoinColumn referred to in the mapping on Bids in Item refers to the Foreign Key in the Bid table; we are explicitly telling Hibernate “the Foreign Key to Item in Bids is a column named itemid”

Another way to phrase that is – we are telling Item “find all rows in Bid where bid.itemid = item.id”

If we annotate the Bids in Item with mappedBy, we’re also telling Item how it relates to Bids, but with an important caveat — we’re telling Item it is not responsible for managing that relationship.

The decision then comes to what behavior you want. Usually, when I’m mapping child collections, I want the parent to be responsible for the collection. The reason is I want to be able to save the parent item, and have Hibernate automatically recognize I want it to also save any changes to the children.

If this is not the behavior you want (which is quite possible), then mappedBy would be the more appropriate choice.

In this example, though, you’d have mappedBy on both ends of the relationship, which sort of defeats the purpose.

@OneToMany(
mappedBy = “item”, cascade=CascadeType.ALL)
@OrderBy(“userId,date,amount”)
public List getBids() {
return bids;
}
Correct me if i am wrong.
Prem

Does it not look like the itemid is going to be in the ITEM table?

Thanks
Prem

That is one element I omitted from the example.

For example, if you’re using MySQL or SQL Server, you can use the built in identity generation:
@Id @GeneratedValue(strategy=GenerationType.IDENTITY)
public Integer getId() {
return id;
}

When using Oracle, I usually use the sequence strategy:

@Id @GeneratedValue(strategy=GenerationType.SEQUENCE, generator=”ITEMID_SEQ”)
public Integer getId() {
return id;
}

But the mapping does not work if I add a database constraint saying that the itemid column in item table is not null. Then when I try to save an item class with associated bids I get an error saying “not-null property references a null or transient value”.

Any pointers?