Inserting parent/child rows in Hibernate with autoincrement index throws error - scala

Question

I have the following Hibernate classes in Scala, where one Group has many Items. Note that the #Id of the Group class has an autoincrement annotation.
#Entity
#Table(name = "items")
class Item extends Serializable {
#Id
#ManyToOne
#JoinColumn(name="group_sk", nullable=false)
var group: Group = _
#Id
var index: Int = _
var name: String = _
def canEqual(a: Any) = a.isInstanceOf[Item]
override def equals(that: Any): Boolean =
that match {
case that: Item => that.canEqual(this) && this.hashCode == that.hashCode
case _ => false
}
override def hashCode: Int = {
val prime = 31
var result = 1
result = prime * result + group.sk;
result = prime * result + index
return result
}
}
#Entity
#Table(name = "groups")
class Group {
#Id
#GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "group_generator")
#SequenceGenerator(name="group_generator",
sequenceName = "GroupSeq", allocationSize = 1)
var sk: Int = _
#Column(name = "group_name")
var name: String = _
#OneToMany
#JoinColumn(name="group_sk")
var items: java.util.List[Item] = _
}
I try to insert one group with a related item, where both the Group should have an auto incremented Id:
session.beginTransaction
val group = new Group
group.name = "Group name"
group.items = new java.util.ArrayList[Item]()
val item1 = new Item
item1.group = group
item1.index = 1
item1.name = "Item 1"
group.items.add(item1)
session.save(group)
session.getTransaction.commit
The exception I get is
Caused by: javax.persistence.OptimisticLockException: Batch update
returned unexpected row count from update [0]; actual row count: 0;
expected: 1
And the Hibernate sql log shows:
Hibernate: select GroupSeq.nextval from dummy
Hibernate: insert into groups (group_name, sk) values (?, ?)
Hibernate: update items set group_sk=? where index=? and group_sk=?
Note that the last update statement doesn't make sense because you won't update the value of group_sk where the column is also in the condition. Moreover, there's no insert statement of the items table.
How to fix this problem?

Answer 1

You need to set cascade type on your OneToMany relationship to tell Hibernate how to mange Items collection of the Group class. So for example something like this should work:
#OneToMany(cascade=CascadeType.ALL)
#JoinColumn(name="group_sk")
var items: java.util.List[Item] = _