JSF2.0, JPA: How to set list element (mapped in @OneToMany)

Question

I'm looking for good practices and clean solution to my problem. There are 2 entity classes:

@Entity
public class Site implements Serializable {
  ...
  @OneToMany(mappedBy = "site")
  private List<SiteIp> siteIpList;
  ...
  public List<SiteIp> getSiteIpList() {
    return siteIpList;
  }
  public void setSiteIpList(List<SiteIp> siteIpList) {
    this.siteIpList = siteIpList;
  }
}

@Entity
@IdClass(SiteIpPK.class)
public class SiteIp implements Serializable {

  @Id
  @ManyToOne(fetch = FetchType.LAZY)
  private Site site;

  @Id
  private int idx;

  private String ip;

  /* other stuff such as constructors, getters and setters */

}

SiteIpPK has 2 columns, it should be clean :) Obviously, this is commonly used model in world.

Next, there is a view layer. JSF page has 3 fields showing SiteIp.ip for given site and idx. As far, I've wrote helper getter method on Site entity:

public String getIpForIdx(Integer idx) {
  // there's no simple siteIpList.get(idx), because of additional logic in getter
  // so let's iterate through entire list

  for (SiteIp siteIp : this.siteIpList) {
    if (/* other logic returns true value && */ siteIp.getIdx() == idx) {
      return siteIp.getIp();
    }
  }

  return null;
}

JSF expression language is constructed as follows:

<h:inputText id="sync1_ip" value="#{siteController.editContext.site.getIpForIdx(1)}" />

Now, when page is accessed, proper IP values is propagated to input text field, as far it's all good. But, when IP changed and form is submitted, EL throws exception:

javax.el.PropertyNotWritableException: /edit/siteEdit.xhtml @47,123 value="#{siteController.editContext.site.getIpForIdx(1)}": Illegal Syntax for Set Operation

I understand and acknowledge that, so there is my question:

What are best practices to handle this issue? Somewhat awful solution is to write as many helper methods as unique indexes exists:

public String getIp1() {
    return this.IpForIdx(1);
}
public String getIp2() {
    return this.IpForIdx(2);
}
/* ... */

public void setIp1(String newIp) {
    this.siteIpList.add(1, newIp);
}
public void setIp2(String newIp) {
    this.siteIpList.add(2, newIp);
}
/* ... and so on... */

with JSF EL:

<h:inputText id="sync1_ip" value="#{siteController.editContext.site.ip1}" />

Are there other, more flexible and beautiful solutions?

score 1 · Answer 1 · answered Feb 15 '13 at 09:44

You should better google for 'composite primary key with JPA'. But as you're new here, below goes a simple explanation and a working solution.

Small explanation

Composite primary keys are themselves classes with @Embeddable annotation. And they become a primary key in your @Entity class as soon as you mark your primary composite key field with @EmbeddedId. The only thing left is to implement equals and hashcode appropriately in both classes.

Solution

The solution consists of an @Entity class

@Entity
@Table(name="...")
@AssociationOverride(name = "pk.site", joinColumns = @JoinColumn(name = "..."))
public class SiteIp implements Serializable {

    private SiteIpPk pk = new SiteIpPK();
    private String ip;

    public SiteIp() {   }

    @EmbeddedId
    public SiteIpPK getPk() {
        return pk;
    }
    public void setPk(SiteIpPk pk) {
        this.pk = pk;
    } 

    @Transient
    public Site getSite() {
        return pk.getSite();
    }
    public void setSite(Site site) {
        pk.setSite(site);
    }

    @Transient
    public Integer getIdx() {
        return pk.getIdx();
    }
    public void setIdx(Integer idx) {
        pk.setIdx(idx);
    }

    @Column(name="...")
    public String getIp() {
        return ip;
    }
    public void setIp(String ip) {
        this.ip = ip;
    }

    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        SiteIp that = (SiteIp) o;
        if (pk != null ? !pk.equals(that.pk) : that.pk != null)
            return false;
        return true;
    }

    public int hashCode() {
        return (pk != null ? pk.hashCode() : 0);
    }

}

and @Embeddable class

@Embeddable
public class SiteIpPk implements Serializable {

    private Site site;
    private Integer idx;

    @ManyToOne
    public Site getSite() {
        return site();
    }
    public void setSite(Site site) {
        this.site = site;
    }

    @Column(name="...", nullable = false)
    public Integer getIdx() {
        return idx;
    }
    public void setIdx(Integer idx) {
        this.idx = idx;
    }

    public boolean equals(Object o) {
        if (this == o)
            return true;
        if (o == null || getClass() != o.getClass())
            return false;
        SiteIpPk that = (SiteIpPk) o;
        if (site != null ? !site.equals(that.site) : that.site != null)
            return false;
        if (idx != null ? !idx.equals(that.idx) : that.idx != null)
            return false;
        return true;
    }

    public int hashCode() {
        int result;
        result = (site != null ? site.hashCode() : 0);
        result = 17 * result + (idx != null ? idx.hashCode() : 0);
        return result;
    }

}

In the end, learn more yourself and check if the problem has already been investigated!

JSF2.0, JPA: How to set list element (mapped in @OneToMany)

1 Answers1

Small explanation

Solution