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This article mainly explains "how to realize Hibernate one-to-many data association". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "how to implement Hibernate one-to-many data association".

1. Data model

two。 Table definition sql

Use sample; DROP TABLE addresses; DROP TABLE user; CREATE TABLE T_User (id INT NOT NULL AUTO_INCREMENT, name VARCHAR (50), age INT, PRIMARY KEY (id)) CREATE TABLE T_Address (id INT NOT NULL AUTO_INCREMENT, address VARCHAR, zipcode VARCHAR, tel VARCHAR, type VARCHAR, user_id INT NOT NULL, idx INT, PRIMARY KEY (id), INDEX (user_id)) CONSTRAINT FK_T_Address_1 FOREIGN KEY (user_id) REFERENCES T_User (id))

POJO class

TUser.java

Package cn.blogjava.start; import java.util.Set; public class TUser implements java.io.Serializable {/ / Fields private Integer id; private Integer age; private String name; private Set address; / / Constructors public Integer getAge () {return age;} public void setAge (Integer age) {this.age = age } public Set getAddress () {return address;} public void setAddress (Set address) {this.address = address;} / * * default constructor * / public TUser () {} / * * constructor with id * / public TUser (Integer id) {this.id = id } / / Property accessors public Integer getId () {return this.id;} public void setId (Integer id) {this.id = id;} public String getName () {return this.name;} public void setName (String name) {this.name = name;}}

TAddress.java

Package cn.blogjava.start; import java.io.Serializable; public class TAddress implements Serializable {private Integer id; private String address; private String zipcode; private String tel; private String type; private Integer userId; private Integer idx; public Integer getId () {return id;} public void setId (Integer id) {this.id = id } public String getAddress () {return address;} public void setAddress (String address) {this.address = address;} public Integer getIdx () {return idx;} public void setIdx (Integer idx) {this.idx = idx;} public String getTel () {return tel } public void setTel (String tel) {this.tel = tel;} public String getType () {return type;} public void setType (String type) {this.type = type;} public Integer getUserId () {return userId;} public void setUserId (Integer userId) {this.userId = userId } public String getZipcode () {return zipcode;} public void setZipcode (String zipcode) {this.zipcode = zipcode;}}

3. Configuration file

TUser.hbm.xml

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> id > key > set > class > hibernate-mapping >

TAddress.hbm.xml

Note: the user_id field is not configured.

"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> id > class > hibernate-mapping >

4. Test code

Package cn.blogjava.start; import java.util.HashSet; import java.util.Iterator; import java.util.List; import junit.framework.Assert; import junit.framework.TestCase; import org.hibernate.HibernateException; import org.hibernate.Session; import org.hibernate.SessionFactory; import org.hibernate.Transaction; import org.hibernate.cfg.Configuration; public class HibernateTest extends TestCase {Session session = null Protected void setUp () {try {Configuration config = new Configuration () .configure (); SessionFactory sessionFactory = config.buildSessionFactory (); session = sessionFactory.openSession ();} catch (HibernateException e) {e.printStackTrace () }} protected void tearDown () {try {session.close ();} catch (HibernateException e) {e.printStackTrace () }} / * object persistence testing (Insert method) * / public void testInsert () {Transaction tran = null; try {TUser user = new TUser (); user.setName ("byf") User.setAge (new Integer (26)); TAddress addr = new TAddress (); addr.setTel ("1123"); addr.setZipcode ("233123"); addr.setAddress ("HongKong"); TAddress addr2 = new TAddress (); addr2.setTel ("139") Addr2.setZipcode ("116001"); addr2.setAddress ("dalian"); TAddress addr3 = new TAddress (); addr3.setTel ("100080"); addr3.setZipcode ("100080"); addr3.setAddress ("beijing") / / set correlation HashSet set = new HashSet (); set.add (addr); set.add (addr2); set.add (addr3); user.setAddress (set); tran = session.beginTransaction () / / insert user information session.save (user); session.flush (); tran.commit (); Assert.assertEquals (user.getId (). IntValue () > 0, true);} catch (HibernateException e) {e.printStackTrace () Assert.fail (e.getMessage ()); if (tran! = null) {try {tran.rollback ();} catch (Exception E1) {e1.printStackTrace () } / * object read test (Select method) * / public void testSelect () {String hql = "from TUser where name='byf'"; try {List userList = session.createQuery (hql) .list () TUser user = (TUser) userList.get (0); System.out.println ("user name is" + user.getName ()); for (Iterator iter = user.getAddress (). Iterator (); iter.hasNext ();) {TAddress addr = (TAddress) iter.next () System.out.println ("user address is" + addr.getAddress ());} Assert.assertEquals (user.getName (), "byf");} catch (Exception e) {e.printStackTrace (); Assert.fail (e.getMessage ());}

Description:

One problem is that because it is an one-way association, in order to maintain the relationship, we can only cascade and update the passive party through the master. If the field of the associated party is a NOT NULL attribute, a constraint violation may occur when Hibernate creates or updates the association relationship.

In the example, the user_id in the T _ addresses table is NOT NULL, if TAddress.hbm.xml maps all fields. Create a user and give her address information, and for the T_ addresses table, Hibernate one to many executes two sql statements to hold the address information.

To execute two SQL statements, it is because the association is one-way, that is, for the TAddress object, you do not know which TUser object you should associate with, so you can only set user_id to a null value.

After that, according to the configuration file

Key > set > at this point, I believe you have a deeper understanding of "how to achieve Hibernate one-to-many data association". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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