how to use a composite primary key as foreign key

[Syed Khurram Anwar]

I have a class HardwareConfiguration which contains a composite primary key. I have done that using JPA Annotations. Here is the code:

@Entity
@Table(name="hardwareConfiguration")
public class HardwareConfiguration {

    @Id
    HardwareConfigurationPK primaryKey = new HardwareConfigurationPK();

    @Column(name="description", length=100)
    private String description;

    @Column(name="frozenYN")    
    private Boolean frozenYN;

    @ManyToOne(targetEntity=Machine.class)
    @JoinColumn(name="machineId", nullable=false)
    private Machine machine;

    @OneToMany(mappedBy="hardwareConfiguration")
    private Set<MachineLevelVariables> machineLevelVariables;

    public HardwareConfiguration () {
        frozenYN = Boolean.FALSE;
    }

    public String getDescription () {
        return description;
    }

    public void setDescription (String val) {
        this.description = val;
    }

    public boolean getFrozenYN () {
        return frozenYN;
    }

    public void setFrozenYN (boolean val) {
        this.frozenYN = val;
    }

    public Machine getMachine () {
        return machine;
    }

    public void setMachine (Machine val) {
        this.machine = val;
    }

    public Set<MachineLevelVariables> getMachineLevelVariables () {
        return machineLevelVariables;
    }

    public void setMachineLevelVariables (Set<MachineLevelVariables> val) {
        this.machineLevelVariables = val;
    }

    public HardwareConfigurationPK getPrimaryKey() {
        return primaryKey;
    }

    public void setPrimaryKey(HardwareConfigurationPK primaryKey) {
        this.primaryKey = primaryKey;
    }
}

Here is the class for composite primary key:

@Embeddable
public class HardwareConfigurationPK implements Serializable {

    private Long id;
    private Long version;

    public HardwareConfigurationPK() {

    }

    public HardwareConfigurationPK(Long id, Long version) {
        this.id = id;
        this.version = version;
    }

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public Long getVersion() {
        return version;
    }

    public void setVersion(Long version) {
        this.version = version;
    }

    @Override
    public boolean equals(Object obj) {
              
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }

        final HardwareConfigurationPK other = (HardwareConfigurationPK) obj;
        if (id == null) {
            if (other.id != null) {
                return false;
            }
        } else if (!id.equals(other.id)) {
            return false;
        }
        if (version == null) {
            if (other.version != null) {
                return false;
            }
        } else if (!version.equals(other.version)) {
            return false;
        }
        return true;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((id == null) ? 0 : id.hashCode());
        result = prime * result + ((version == null) ? 0 : version.hashCode());
        return result; 
    }
}

Now I want to use this composite primary key as a foreign key in another class. How can I do that using annotations. here is the class which is using this composite key as foreign key:

@Entity
@Table(name="configInfo")
public class ConfigInfo {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    @Column(name="id", nullable=false)
    private Long id;

    private HardwareConfiguration hardwareConfiguration; // I want help here. What annotations should be applied here?

    public ConfigInfo () {
    }

    public HardwareConfiguration getHardwareConfiguration () {
        return hardwareConfiguration;
    }

    public void setHardwareConfiguration (HardwareConfiguration val) {
        this.hardwareConfiguration = val;
    }

    public Long getId () {
        return id;
    }

    public void setId (Long val) {
        this.id = val;
    }

}

[James Sutherland]

You should not need to do anything, as the hardwareConfiguration will be defaulted to a OneToOne using a foreign key to both Id fields.
You could annotate it as a @OneToOne, and include a @JoinColumn for each foreign key column to the HardwareConfiguration (id and version).

Note that your annotations for HardwareConfiguration are not correct, they should use @EmbeddedId not @Id.

[Syed Khurram Anwar]

Thanks. I am new to Hibernate. Would you please tell me the syntax that how will I use this key in another class as foreign key?

I read the book "Hibernate Made Easy" by Cameron. He has explained 3 ways to use embeddable class

1 - @id

2 - @IdClass

3 - @EmbeddedId

I have used the first one.

[Martin Lopez Ochoteco]

I think @EmbeddedId is the best approach. @IdClass is only declared in JPAs new specification because of EJB2 compatibility.

Code:

@Entity
@Table(name="hardwareConfiguration") 
public class HardwareConfiguration {  

@EmbeddedId
private HardwareConfigurationPK primaryKey = new HardwareConfigurationPK();
...

[Syed Khurram Anwar]

How to use it in the following class as foreign key?

 @Entity  
 @Table(name="configInfo")  
 public class ConfigInfo {  
   
     @Id  
     @GeneratedValue(strategy=GenerationType.AUTO)  
     @Column(name="id", nullable=false)  
     private Long id;  
   
     private HardwareConfiguration hardwareConfiguration; // I want help here. What annotations should be applied here?  
   
     public ConfigInfo () {  
     }  
   
     public HardwareConfiguration getHardwareConfiguration () {  
         return hardwareConfiguration;  
     }  
   
     public void setHardwareConfiguration (HardwareConfiguration val) {  
         this.hardwareConfiguration = val;  
     }  
   
     public Long getId () {  
         return id;  
     }  
   
     public void setId (Long val) {  
         this.id = val;  
     }  
   
 }