Marco Schwarz wrote:
@MappedSuperclass
@Inheritance(strategy=InheritanceType.TABLE_PER_CLASS)
class ModelObject {
@Transient
ModelObject parent;
@OneToMany(cascade={CascadeType.ALL}, fetch=FetchType.EAGER)
List<ModelObject> children;
}
When I start my app the openjpa create 4 tables (Company,
Company_children, Emplpyer and Employer_children).
How can I make only 2 tables?
Here's my guess:
First, use the "mappedBy" property of the @OneToMany annotation, like this:
@Entity
class ModelObject {
...
@ManyToOne
ModelObject parent;
@OneToMany(mappedBy="parent")
List<ModelObject> children;
...
}
This way, an extra join table won't be necessary to encode the parent
child relationship. Only the "parent_id" column in the "ModelObject"
table will be used to encode the relationship.
Next, you want to make sure you're using "single table" mapping to
encode inheritance relations. This way all classes derived from
ModelObject should utilize the same table. Although single table is
supposed to be the default inheritance strategy, it might not hurt to
explicitly state it:
@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
class ModelObject {
...
@ManyToOne
ModelObject parent;
@OneToMany(mappedBy="parent")
List<ModelObject> children;
...
}
