"SSH Three frames" Hibernate Foundation Sixth: mapping, analysis and adding and querying of many-to-one relational relationships

Here's an example: the relationship between the department and the employee.

A department can correspond to multiple employees, which is obviously a many-to-one relationship.

We need to create two entity classes: Employee, Department (Department)

Employee class: Employee.java (In this case we have added a department-type attribute to do the correlation)

Package Cn.itcast.hibernate.domain;public class Employee {private int id;private String name;private Department depart; 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;} Public Department Getdepart () {return depart;} public void Setdepart (Department depart) {This.depart = Depart;}}

Department Department.java

Package Cn.itcast.hibernate.domain;public class Department {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;}}

Then, we will build their mapping files in their directory:

Employee.hbm.xml (Here we have added a <many-to-one/> tag to specify the mapping)

<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "http://hibernate.sourceforge.net/ Hibernate-mapping-3.0.dtd ">
Department.hbm.xml
<?xml version= "1.0"? ><! DOCTYPE hibernate-mapping Public "-//hibernate/hibernate mapping DTD 3.0//en" "http://hibernate.sourceforge.net/ Hibernate-mapping-3.0.dtd ">

Finally we need to build hibernate.cfg.xml, which is used to establish a mapping file that connects to the database and loads each entity class:
<?xml version= ' 1.0 ' encoding= ' utf-8 '?> <! DOCTYPE hibernate-configuration Public "-//hibernate/hibernate configuration DTD 3.0//en" "http// Hibernate.sourceforge.net/hibernate-configuration-3.0.dtd ">
By this point, all the configurations have been set up and you are ready to start testing.
We create a Many2one.java file:
Package Cn.itcast.hibernate;import Org.hibernate.session;import Org.hibernate.transaction;import Cn.itcast.hibernate.domain.department;import Cn.itcast.hibernate.domain.employee;public class Many2One {public static void Main (string[] arg) {add (); Employee emp = query (1);} Static Department Add () {Session s = null; Transaction tx = Null;try{department depart = new Department ();d epart.setname ("Depart name"); Employee EMP = new Employee (); Emp.setdepart (depart);   Establish an association relationship of two objects emp.setname ("emp name"); s = hibernateutil.getsession (); tx = S.begintransaction (); S.save (EMP); The EMP object and depart object are saved in different order and there will be some difference s.save (depart); If an employee (EMP) is inserted after the department (depart), it generates three database statements//Because the EMP depart_id field is not inserted after both insertions, so there is a last statement to insert Tx.commit (); return depart ;} Finally{if (s!=null) {s.close ();}}} static Employee query (int empId) {Session s = null; Transaction tx = Null;try{s = Hibernateutil.getsession (); tx = S.begintransaction (); Employee EMP = (employee) s.get (Employee.class, empId); Query System.out.println (Emp.getname ()) by ID; Query Employee NameSystem.out.println (Emp.getdepart (). GetName ()); According to the employee inquires into which department tx.commit (); return EMP;} Finally{if (s!=null) {s.close ();}}}}

The basic operation of many-to-one is complete.
Therefore, hibernate can directly manipulate the relational database with object-oriented language.

"SSH Three frames" Hibernate Foundation Sixth: mapping, analysis and adding and querying of many-to-one relational relationships