How to map a composite key with JPA and Hibernate?

Question

In this code, how to generate a Java class for the composite key (how to composite key in hibernate):

create table Time (
     levelStation int(15) not null,         


        

Answer 1

Using hbm.xml

    <composite-id>

        <!--<key-many-to-one name="productId" class="databaselayer.users.UserDB" column="user_name"/>-->
        <key-property name="productId" column="PRODUCT_Product_ID" type="int"/>
        <key-property name="categoryId" column="categories_id" type="int" />
    </composite-id>  

Using Annotation

Composite Key Class

public  class PK implements Serializable{
    private int PRODUCT_Product_ID ;    
    private int categories_id ;

    public PK(int productId, int categoryId) {
        this.PRODUCT_Product_ID = productId;
        this.categories_id = categoryId;
    }

    public int getPRODUCT_Product_ID() {
        return PRODUCT_Product_ID;
    }

    public void setPRODUCT_Product_ID(int PRODUCT_Product_ID) {
        this.PRODUCT_Product_ID = PRODUCT_Product_ID;
    }

    public int getCategories_id() {
        return categories_id;
    }

    public void setCategories_id(int categories_id) {
        this.categories_id = categories_id;
    }

    private PK() { }

    @Override
    public boolean equals(Object o) {
        if ( this == o ) {
            return true;
        }

        if ( o == null || getClass() != o.getClass() ) {
            return false;
        }

        PK pk = (PK) o;
        return Objects.equals(PRODUCT_Product_ID, pk.PRODUCT_Product_ID ) &&
                Objects.equals(categories_id, pk.categories_id );
    }

    @Override
    public int hashCode() {
        return Objects.hash(PRODUCT_Product_ID, categories_id );
    }
}

Entity Class

@Entity(name = "product_category")
@IdClass( PK.class )
public  class ProductCategory implements Serializable {
    @Id    
    private int PRODUCT_Product_ID ;   

    @Id 
    private int categories_id ;

    public ProductCategory(int productId, int categoryId) {
        this.PRODUCT_Product_ID = productId ;
        this.categories_id = categoryId;
    }

    public ProductCategory() { }

    public int getPRODUCT_Product_ID() {
        return PRODUCT_Product_ID;
    }

    public void setPRODUCT_Product_ID(int PRODUCT_Product_ID) {
        this.PRODUCT_Product_ID = PRODUCT_Product_ID;
    }

    public int getCategories_id() {
        return categories_id;
    }

    public void setCategories_id(int categories_id) {
        this.categories_id = categories_id;
    }

    public void setId(PK id) {
        this.PRODUCT_Product_ID = id.getPRODUCT_Product_ID();
        this.categories_id = id.getCategories_id();
    }

    public PK getId() {
        return new PK(
            PRODUCT_Product_ID,
            categories_id
        );
    }    
}

Answer 2

Another option is to map is as a Map of composite elements in the ConfPath table.

This mapping would benefit from an index on (ConfPathID,levelStation) though.

public class ConfPath {
    private Map<Long,Time> timeForLevelStation = new HashMap<Long,Time>();

    public Time getTime(long levelStation) {
        return timeForLevelStation.get(levelStation);
    }

    public void putTime(long levelStation, Time newValue) {
        timeForLevelStation.put(levelStation, newValue);
    }
}

public class Time {
    String src;
    String dst;
    long distance;
    long price;

    public long getDistance() {
        return distance;
    }

    public void setDistance(long distance) {
        this.distance = distance;
    }

    public String getDst() {
        return dst;
    }

    public void setDst(String dst) {
        this.dst = dst;
    }

    public long getPrice() {
        return price;
    }

    public void setPrice(long price) {
        this.price = price;
    }

    public String getSrc() {
        return src;
    }

    public void setSrc(String src) {
        this.src = src;
    }
}

Mapping:

<class name="ConfPath" table="ConfPath">
    <id column="ID" name="id">
        <generator class="native"/>
    </id>
    <map cascade="all-delete-orphan" name="values" table="example"
            lazy="extra">
        <key column="ConfPathID"/>
        <map-key type="long" column="levelStation"/>
        <composite-element class="Time">
            <property name="src" column="src" type="string" length="100"/>
            <property name="dst" column="dst" type="string" length="100"/>
            <property name="distance" column="distance"/>
            <property name="price" column="price"/>
        </composite-element>
    </map>
</class>