Question

Can hibernate resolve mapping across more than one table.

Here is example:

• Class Manufacturer, table MANUFACTURER
• Class Car, table CAR Class
• CarType, table CAR_TYPE

ORM Model

• MANUFACTURER one to many CAR (MANUFACTURER_ID_FK in table CAR)
• CAR many to one CAR_TYPE (CAR_TYPE_ID_FK in table CAR)

What I want is hibernate mapping that will resolve all CAR TYPES for given Manufacturer?

So if I wanted to get all cars I would write

     <set name="cars" inverse="true" cascade="all,delete-orphan" lazy="false" >
        <key property-ref="manufacturerIdFk">
            <column name="MANUFACTURER_ID_FK " precision="22" scale="0" not-null="true"/>
        </key>
        <one-to-many class="foo.bar.Car" />
    </set>

What I need is how to get car types for manufacturer?

<set name="carTypes" inverse="true" cascade="all,delete-orphan" lazy="false" >
  ???
</set>

Thank you and please don’t answer just get it from “cars” 🙂 Solution what I would like to implement should completely really on hibernate mapping to do “heavy lifting”. Thanks again.

Answer 1

You can map directly manufacturer.carTypes collection as a ManyToMany relationship based on the association table : CAR.

Here is an example (Annotations) :
In class Manufacturer

@ManyToMany(fetch = FetchType.LAZY)
@JoinTable(name = "CAR", joinColumns = @JoinColumn(name = "MANUFACTURER_ID_FK"), 
inverseJoinColumns = @JoinColumn(name = "CAR_TYPE_ID_FK"))
private Set<CarType> carTypes;