JPA映射到Map <Object, Interger>

Question

I've 3 tables: - lots: has column gen_id
- onhand_quantities: has column gen_id,sub_inventory_code, quantity
- subinventory: has column sub_inventory_code

I map to 2 objects: Lots, SubInventory and I would like to mapping in object Lots with property is: Map<SubInventory, Integer> getOnhandQuantity()
Integer type in this Map is value of quantity column. Please help me.

Answer 1

Just a brief search in Hibernate document give me information on using an associated entity as key of a Map (aka Ternary Association )

Quoted from the manual:

There are three possible approaches to mapping a ternary association. One approach is to use a Map with an association as its index:

Example 7.31. Ternary association mapping

 @Entity public class Company { @Id int id; ... @OneToMany // unidirectional @MapKeyJoinColumn(name="employee_id") Map<Employee, Contract> contracts; } // or <map name="contracts"> <key column="employer_id" not-null="true"/> <map-key-many-to-many column="employee_id" class="Employee"/> <one-to-many class="Contract"/> </map> 

A second approach is to remodel the association as an entity class. This is the most common approach. A final alternative is to use composite elements, which will be discussed later.

To map it back to your original example: Company -> Lots, Employee -> SubInventory, Contract -> OnhandQuantity

Personally I would rather make them as a simple relationship, and construct Map etc on the fly whenever it is needed.

---

Haven't tried, but a further look get me to an example in @MapKeyColumn , which in combination with the above sample, should give something reasonable like:

class Lot {
    @ElementCollection
    @MapKeyJoinColumn(name="sub_inventory_id")
    @CollectionTable(name="onhand_quantities")
    @Column(name="quantity")
    private Map<SubInventory, Integer> onhandQuantities;

}

Answer 2

The below code in the Lots entity should do.

@ElementCollection(fetch = FetchType.LAZY)
@CollectionTable(name = "ONHAND_QUANTITIES", joinColumns= @JoinColumn(name="GEN_ID"))
@MapKeyJoinColumn(name="SUBINVENTORY_CODE")
@Column(name="QUANTITY")
private Map<SubInventory, Integer> onHandQuantity;

I am trying to test this.

I got this solution from the below link.

Reference key issue while doing many to many relationship using @ElementCollection, @MapKeyJoinColumn

@Entity
@Table(name = "LOTS")
public class Lots implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @GeneratedValue
    @Column(name = "GEN_ID")
    private Long id;

    @ElementCollection(fetch = FetchType.LAZY)
    @CollectionTable(name = "ONHAND_QUANTITIES", joinColumns= @JoinColumn(name="GEN_ID"))
    @MapKeyJoinColumn(name="SUBINVENTORY_CODE")
    @Column(name="QUANTITY")
    private Map<SubInventory, Integer> onHandQuantity;

   ......// getters and setters
}


@Entity
@Table(name = "SUBINVENTORY")
public class SubInventory implements Serializable {

    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue
    @Column(name="SUBINVENTORY_CODE")
    private Long id;

    ......// getters and setters
}