Hibernate learning -------- combining multiple fields for primary keys (for Annotation versions, xml is not commonly used)

Hibernate learning -------- combining multiple fields for primary keys (for Annotation versions, xml is not commonly used)

Here we record the annotation method of combining primary keys in hibernate.

Hibernate-annotations This document describes how to use annotation to combine primary keys.

The following statements define the primary key combination:

1. annotation of the component class as @ Embeddable, and Annotation of the Component Property as @ Id

2. annotation of component properties as @ EmbeddedId

3. annotation of the class as @ IdClass, and Annotation of all attributes belonging to the primary key in the object as @ Id

Here we will only introduce the two most commonly used methods (the second and the third)

(1) @ EmbeddedId

Create a new Teacher Class and add attributes to the class, including the primary key class TeacherPK

Package com. team. model; import javax. persistence. column; import javax. persistence. embeddedId; import javax. persistence. entity; @ Entitypublic class Teacher {private TeacherPK pk; // primary key class private String sex; @ EmbeddedId // primary key public TeacherPK getPk () {return pk ;} public void setPk (TeacherPK pk) {this. pk = pk;} @ Column (length = 20) public String getSex () {return sex;} public void setSex (String sex) {this. sex = sex ;}}

Write the primary key class TeacherPK. java. Note that the Serializable interface is implemented and the equals and hashCode methods are rewritten.

Package com. team. model; import java. io. serializable; public class TeacherPK implements Serializable {private int id; private String name; public int getId () {return id;} public void setId (int id) {this. id = id;} public String getName () {return name;} public void setName (String name) {this. name = name;} // two methods that must be overwritten @ Overridepublic boolean equals (Object obj) {if (obj instanceof TeacherPK) // first determine whether it is TeacherPK type {TeacherPK pk = (TeacherPK) obj; if (this. id = pk. getId () & this. name. equals (pk. getName () {return true ;}} return false ;}@ Overridepublic int hashCode () {return super. hashCode ();}}

Add a ing in hibernate. cfg. xml:

Right-click Teacher. java to create the Junit Test class: TeacherTest:

Package com. team. model; import org. hibernate. session; import org. hibernate. sessionFactory; import org. hibernate. cfg. annotationConfiguration; import org. hibernate. cfg. configuration; import org. junit. afterClass; import org. junit. beforeClass; import org. junit. test; public class TeacherTest {private static Configuration cfg = null; private static SessionFactory sf = null; @ BeforeClasspublic static void beforeClass () {Configuration cfg = new AnnotationConfiguration (); sf = cfg. configure (). buildSessionFactory () ;}@ AfterClasspublic static void afterClass () {sf. close () ;}@ Testpublic void test () {TeacherPK = new TeacherPK (); pk. setId (1); pk. setName ("Zhang San"); Teacher teacher = new Teacher (); teacher. setPk (pk); teacher. setSex ("male"); Session session = sf. openSession (); session. beginTransaction (); session. save (teacher); session. getTransaction (). commit (); session. close ();}}

Running result: (Table creation Statement)

Create table Teacher (id integer not null, name varchar (255) not null, sex varchar (20), primary key (id, name ))

View the MySQL database:

Vc/kernel + kernel/nT0LXE1ve8/kernel + csung vcd4kpha + kernel + csung vcd4kpha + CrPM0PLI58/Co7o8L3A + kernel =" brush: java; "> package com. team. model; import javax. persistence. column; import javax. persistence. embeddedId; import javax. persistence. entity; import javax. persistence. id; import javax. persistence. idClass; @ Entity @ IdClass (value = TeacherPK. class) public class Teacher {private int id; private String name; // private TeacherPK pk; // primary key class private String sex;/* @ EmbeddedId // primary key public TeacherPK getPk () {return pk;} public void setPk (TeacherPK pk) {this. pk = pk;} */@ Id // primary key 1 public int getId () {return id;} public void setId (int id) {this. id = id;} @ Id // primary key 2 public String getName () {return name;} public void setName (String name) {this. name = name ;}@ Column (length = 20) public String getSex () {return sex;} public void setSex (String sex) {this. sex = sex ;}}Test class:

Package com. team. model; import org. hibernate. session; import org. hibernate. sessionFactory; import org. hibernate. cfg. annotationConfiguration; import org. hibernate. cfg. configuration; import org. junit. afterClass; import org. junit. beforeClass; import org. junit. test; public class TeacherTest {private static Configuration cfg = null; private static SessionFactory sf = null; @ BeforeClasspublic static void beforeClass () {Configuration cfg = new AnnotationConfiguration (); sf = cfg. configure (). buildSessionFactory () ;}@ AfterClasspublic static void afterClass () {sf. close () ;}@ Testpublic void test () {/* TeacherPK = new TeacherPK (); pk. setId (1); pk. setName ("Zhang San"); */Teacher teacher = new Teacher (); teacher. setId (1); teacher. setName ("Li Si"); // teacher. setPk (pk); teacher. setSex ("male"); Session session = sf. openSession (); session. beginTransaction (); session. save (teacher); session. getTransaction (). commit (); session. close ();}}

The running result is the same as the previous one.