Foreign key problem in Java Persistance API with Netbeans 6.9.1_问答_开发者

I have an error in setting up Java Persistence in Netbeans. I have used MySQL as Back-End Database Server.

My Code is as below,

Database

CREATE TABLE `hub` (
 `hub_ID` INT(11) NOT NULL AUTO_INCREMENT,
 `hub_Name` VARCHAR(45) NOT NULL,
 PRIMARY KEY (`hub_ID`),
 UNIQUE INDEX `hub_Name` (`hub_Name`)
)ENGINE=MyISAM

CREATE TABLE `company` (
 `company_ID` INT(11) NOT NULL AUTO_INCREMENT,
 `company_Name` VARCHAR(45) NOT NULL,
 `company_hub_ID` INT(11) NOT NULL,
 PRIMARY KEY (`company_ID`),
 INDEX `fk_company_hub1` (`company_hub_ID`)
 )

Persistence.xml

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="testJPAPU" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>testjpa.Hub</class>
    <class>testjpa.Company</class>
    <properties>
      <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/logistikumdispatch"/>
      <property name="javax.persistence.jdbc.password" value="rootroot"/>
      <property name="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
      <property name="javax.persistence.jdbc.user" value="root"/>
    </properties>
  </persistence-unit>
</persistence>

Hub.java (Entity Class in Project)

    /*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package testjpa;

import java.io.Serializable;
import java.util.Collection;
import javax.persistence.Basic;
import javax.persistence.CascadeType;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.OneToMany;
import javax.persistence.Table;

/**
 *
 * @author Anjum
 */
@Entity
@Table(name = "hub")
@NamedQueries({
    @NamedQuery(name = "Hub.findAll", query = "SELECT h FROM Hub h"),
    @NamedQuery(name = "Hub.findByHubID", query = "SELECT h FROM Hub h WHERE h.hubID = :hubID"),
    @NamedQuery(name = "Hub.findByHubName", query = "SELECT h FROM Hub h WHERE h.hubName = :hubName")})
public class Hub implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "hub_ID")
    private Integer hubID;
    @Basic(optional = false)
    @Column(name = "hub_Name")
    private String hubName;

    @OneToMany(mappedBy="hub", cascade=CascadeType.ALL)
    @JoinColumn(name="company_hub_ID")
    private Collection<Company> companies;

    public Hub() {
    }

    public Hub(Integer hubID) {
        this.hubID = hubID;
    }

    public Hub(Integer hubID, String hubName) {
        this.hubID = hubID;
        this.hubName = hubName;
    }

    public Integer getHubID() {
        return hubID;
    }

    public void setHubID(Integer hubID) {
        this.hubID = hubID;
    }

    public String getHubName() {
        return hubName;
    }

    public void setHubName(String hubName) {
        this.hubName = hubName;
    }

    public Collection<Company> getCompanies()
    {
        return companies;
    }

    public void setCompanies(Collection<Company> companies)
    {
        this.companies = companies;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (hubID != null ? hubID.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Hub)) {
            return false;
        }
        Hub other = (Hub) object;
        if ((this.hubID == null && other.hubID != null) || (this.hubID != null && !this.hubID.equals(other.hubID))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "testjpa.Hub[hubID=" + hubID + "]";
    }

}

Company.java (Entity Class in Project)

package testjpa;

import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.JoinColumn;
import javax.persistence.ManyToOne;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;

/**
 *
 * @author Anjum
 */
@Entity
@Table(name = "company")
@NamedQueries({
    @NamedQuery(name = "Company.findAll", query = "SELECT c FROM Company c"),
    @NamedQuery(name = "Company.findByCompanyID", query = "SELECT c FROM Company c WHERE c.companyID = :companyID"),
    @NamedQuery(name = "Company.findByCompanyName", query = "SELECT c FROM Company c WHERE c.companyName = :companyName"),
    @NamedQuery(name = "Company.findByCompanyhubID", query = "SELECT c FROM Company c WHERE c.companyhubID = :companyhubID")})
public class Company implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "company_ID")
    private Integer companyID;
    @Basic(optional = false)
    @Column(name = "company_Name")
    private String companyName;
    @Basic(optional = false)
    @Column(name = "company_hub_ID")
    private int companyhubID;
    @ManyToOne()
    @JoinColumn(name="hub_ID", insertable=false, updatable=false)
    private Hub hub;
    public Company() {
    }

    public Company(Integer companyID) {
        this.companyID = companyID;
    }

    public Company(Integer companyID, String companyName, int companyhubID) {
        this.companyID = companyID;
        this.companyName = companyName;
        this.companyhubID = companyhubID;
    }

    public Integer getCompanyID() {
        return companyID;
    }

    public void setCompanyID(Integer companyID) {
        this.companyID = companyID;
    }

    public String getCompanyName() {
        return companyName;
    }

    public void setCompanyName(String companyName) {
        this.companyName = companyName;
    }

    public int getCompanyhubID() {
        return companyhubID;
    }

    public void setCompanyhubID(int companyhubID) {
        this.companyhubID = companyhubID;
    }

    public Hub getHub()
    {
        return hub;
    }

    public void setHub(Hub hub)
    {
        this.hub = hub;
    }

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (companyID != null ? companyID.hashCode() : 0);
        return hash;
    }

    @Override
    public boolean equals(Object object) {
        // TODO: Warning - this method won't work in the case the id fields are not set
        if (!(object instanceof Company)) {
            return false;
        }
        Company other = (Company) object;
        if ((this.companyID == null && other.companyID != null) || (this.companyID != null && !this.companyID.equals(other.companyID))) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "testjpa.Company[companyID=" + companyID + "]";
    }

}

Main Program

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
package testjpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

/**
 *
 * @author Anjum
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("testJPAPU");
        EntityManager em = emf.createEntityManager();

        em.getTransaction().begin();

        Company c1 = new Company();
        c1.setCompanyName("ays");


        Hub h1 = new Hub();
        h1.setHubName("abc");
        em.persist(h1);
        c1.setHub(h1);

        em.persist(c1);
        em.flush();

    }
}

Output

[EL Info]: 2010-09-03 14:39:02.639--ServerSession(3199106)--EclipseLink, version: Eclipse Persistence Services - 2.0.2.v20100323-r6872
[EL Info]: 2010-09-03 14:39:03.371--ServerSession(3199106)--file:/C:/Users/Anjum/Documents/NetBeansProjects/testJPA/build/classes/_testJPAPU login successful

Problem

My problem is that, the foreign key company.company_hub_ID is updated in database wi开发者_开发技巧th comapany.company_name = "ays". But there is always 0 in company.company_hub_ID.

Hub is also updated properly. Means there is no connectivity or JPA problem. Problem lies within the relationship only.

Thanks in advance for helping me.

As already mentioned, you are not supposed to use a JoinColumn on both sides of your OneToMany / ManyToOne association, but only on the owning side (the many side). Remove it from the OneToMany side and fix the column name.

You're also not supposed to have a companyhubID attribute in the Company entity to hold the foreign key (such things are actually supposed to be hidden at the object level). Remove both the attribute and the insertable=false, updatable=false from the JoinColumn.

So the mappings should be:

@Entity
...
public class Hub implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "hub_ID")
    private Integer hubID;
    @Basic(optional = false)
    @Column(name = "hub_Name")
    private String hubName;

    @OneToMany(mappedBy="hub", cascade=CascadeType.ALL)
//    @JoinColumn(name="company_hub_ID") // THIS IS WRONG
    private Collection companies = new HashSet()
    ...
    // method to set both sides of the link of the bidirectional association
    public void addToCompanies(Company company) {
        company.setHub(this);
        this.companies.add(company);
    }
}

And

@Entity
...
public class Company implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "company_ID")
    private Integer companyID;
    @Basic(optional = false)
    @Column(name = "company_Name")
    private String companyName;
//    @Basic(optional = false) 
//    @Column(name = "company_hub_ID")
//    private int companyhubID;          // NO, DON'T

    @ManyToOne()
    @JoinColumn(name="company_hub_ID"/*, insertable=false, updatable=false*/)
    private Hub hub;
    ...
}

Some additional remarks:

Using the IDENTITY strategy for ID generation is fine.
You should use InnoDB tables for referential integrity.

Also note that your demo code is incorrect, you're not setting the association appropriately. It should be:

Company c1 = new Company();
c1.setCompanyName("ays");
Hub h1 = new Hub();
h1.setHubName("abc");
h1.addToCompanies.add(c1);  // set the bidirectional association

em.persist(h1);             // JPA will cascade the persist
em.flush();

Something does not line up between your mapping and the database schema. Is the database schema generated by the JPA provider?

The mapping defines a hub_id join column on the company class, yet the database schema is missing that column (it has "company_hub_ID" instead).

Try the following:

Remove the @JoinColumn from the side of the @OneToMany. @OneToMany+@JoinColumn is only used for mapping unidirectional onetomany associations on a foreign key (without a join table). Your association is a bidirectional onetomany, thus @OneToMany with mappedBy on the inverse side and @ManyToOne + @JoinColumn (optional) on the owning side. Do not set insertable/updatable to false.

I agree with romanb's suggestion.

Since the association is bidirectional, make sure you set "both sides of the link" as pointed out in this post.

Try changing your code like this:

public class Hub {
    ...
    @OneToMany(mappedBy="hub", cascade=CascadeType.ALL)
    private Collection<Company> companies = new ArrayList<Company>();

    ...
    public void addCompany(Company company) {
        company.setHub(this);
        this.companies.add(company);
    }       
    ...
}

public class Company {
    ...         
    @ManyToOne
    @JoinColumn(name="company_hub_ID")
    private Hub hub;    
    ...
}

public class Main {

    public static void Main(String[] args) {
        ...
        Company c1 = new Company();
        c1.setCompanyName("ays");

        Hub h1 = new Hub();
        h1.setHubName("abc");
        h1.addCompany(c1);
        em.persist(h1);
    }

}

Also, use an Id generation strategy other than GenerationType.IDENTITY, as the identifier is not accessible until after the insert has occurred.

Finally I have solved that problem with romanB's support.

Thanks for your help "ROMANB".

Look below how did I solved that, you can use this technique to implement persistence with foreign keys in netbeans.

public class Company implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "company_ID", nullable=true)
    private Integer companyID;
    @Basic(optional = false)
    @Column(name = "company_Name")
    private String companyName;
    @Basic(optional = false)
    @Column(name = "company_hub_ID", nullable=false, updatable=false, insertable=false)
    private int companyhubID;
    @ManyToOne(cascade=CascadeType.ALL)
    @JoinColumn(name="company_hub_ID")
    private Hub hub_ref;
..........
..........

public class Hub implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Basic(optional = false)
    @Column(name = "hub_ID")
    private Integer hubID;
    @Basic(optional = false)
    @Column(name = "hub_Name")
    private String hubName;

    @OneToMany(mappedBy="hub_ref", cascade=CascadeType.ALL)
    private Collection<Company> companies;

    ................
    ................
  \\ in Hub class
public void addCompany(Company company)
    {
        if(this.companies == null)
        {
            this.companies = new ArrayList<Company>();
        }
        this.companies.add(company);
        company.setHub(this);
    }

And finally the main class

 public static void main(String[] args) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("testJPAPU");
        EntityManager em = emf.createEntityManager();



        Company c1 = new Company();
        c1.setCompanyName("ays");

        Hub h1 = new Hub();
        h1.setHubName("abc");

        em.getTransaction().begin();

        h1.addCompany(c1);
        em.persist(h1);

        em.flush();

    }

Use eclipse link 2.0 to get JPA 2.0 support.

Thanks again, and thanks to stack overflow.

Anjum Shrimali.