表结构:
实体类图:
CRUD:
Student:
package com.demo.model; import java.io.UnsupportedEncodingException; import java.util.Set; /**学生信息 * @author wobendiankun *2014-10-19 下午08:54:29 */ public class Student { private int studentId ; private String studentName ; private int age; private Set<Certificate> certificates ; public int getStudentId() { return studentId; } public void setStudentId(int studentId) { this.studentId = studentId; } public String getStudentName() { return studentName; } public void setStudentName(String studentName) { this.studentName = studentName; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public String toString() { String str=""; if(studentName!=null){ try { str=new String(studentName.getBytes("UTF-8")); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } } return "Student [studentId=" + studentId + ", studentName=" + str + ", age=" + age + "]"; } public Set<Certificate> getCertificates() { return certificates; } public void setCertificates(Set<Certificate> certificates) { this.certificates = certificates; } }配置:
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping > <class name="com.demo.model.Student" table="t_student"> <id name="studentId" column="student_id"> <generator class="sequence"> <param name="sequence">SEQ_T_STUDENT</param> </generator> </id> <property name="studentName" column="student_name" /> <property name="age" /> <set name="certificates"> <key column="student_id"></key> <one-to-many class="com.demo.model.Certificate"/> </set> </class> </hibernate-mapping>说明:
<set name="certificates"><key column="student_id"></key>
<one-to-many class="com.demo.model.Certificate"/>
</set>
name:Student类的certificates属性名
<key column="student_id"></key> :关联字段名称
<one-to-many class="com.demo.model.Certificate"/> : Set元素的类全名add:
@Test public void addTest() { Certificate certificate1 = new Certificate(); certificate1.setCertificateName("aa"); certificate1.setCertificateNo("3a10001"); Certificate certificate2 = new Certificate(); certificate2.setCertificateName("bb"); certificate2.setCertificateNo("3a10002"); Set<Certificate> set=new HashSet<Certificate>(); set.add(certificate1); set.add(certificate2); Student student = new Student(); student.setStudentName("钱六"); student.setAge(35); student.setCertificates(set); Session session = null; try { session = HibernateUtil.openSession(); session.beginTransaction(); session.save(student); session.save(certificate1); session.save(certificate2); session.getTransaction().commit(); } catch (Exception e) { session.getTransaction().rollback(); e.printStackTrace(); } finally { HibernateUtil.closeSession(session); } }
发出的SQL:Hibernate: insert into t_student (student_name, age, student_id) values (?, ?, ?) Hibernate: insert into t_certificate (certificate_name, certificate_no, certificate_id) values (?, ?, ?) Hibernate: insert into t_certificate (certificate_name, certificate_no, certificate_id) values (?, ?, ?) Hibernate: update t_certificate set student_id=? where certificate_id=? Hibernate: update t_certificate set student_id=? where certificate_id=?从两条update语句中,我们发现此时的关联字段由one(Student)的一方来维护,这个明显不合适
loadTest:
@Test public void loadTest() { Session session = null; try { session = HibernateUtil.openSession(); session.beginTransaction(); Student student =(Student) session.load(Student.class, 23); System.out.println("姓名:"+student.getStudentName()); System.out.println("数量:"+student.getCertificates().size()); session.getTransaction().commit(); } catch (Exception e) { session.getTransaction().rollback(); e.printStackTrace(); } finally { HibernateUtil.closeSession(session); } }
发出的SQL:Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=? 姓名:钱六 Hibernate: select certificat0_.student_id as student4_0_1_, certificat0_.certificate_id as certific1_1_, certificat0_.certificate_id as certific1_1_0_, certificat0_.certificate_name as certific2_1_0_, certificat0_.certificate_no as certific3_1_0_ from t_certificate certificat0_ where certificat0_.student_id=? 数量:2loadLazyExtra:
在set标签中添加属性:lazy="extra"
<?xml version="1.0"?> <!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN" "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd"> <hibernate-mapping > <class name="com.demo.model.Student" table="t_student"> <id name="studentId" column="student_id"> <generator class="sequence"> <param name="sequence">SEQ_T_STUDENT</param> </generator> </id> <property name="studentName" column="student_name" /> <property name="age" /> <set name="certificates" lazy="extra"><!-- lazy="extra" --> <key column="student_id"></key> <one-to-many class="com.demo.model.Certificate"/> </set> </class> </hibernate-mapping>运行代码:
@Test public void loadLazyExtraTest() { Session session = null; try { session = HibernateUtil.openSession(); session.beginTransaction(); Student student =(Student) session.load(Student.class, 23); System.out.println("姓名:"+student.getStudentName()); System.out.println("数量:"+student.getCertificates().size()); session.getTransaction().commit(); } catch (Exception e) { session.getTransaction().rollback(); e.printStackTrace(); } finally { HibernateUtil.closeSession(session); } }发出的SQL:
Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=? 姓名:钱六 Hibernate: select count(certificate_id) from t_certificate where student_id =? 数量:2loadAssociatesTest:
@Test public void loadAssociatesTest() { Session session = null; try { session = HibernateUtil.openSession(); session.beginTransaction(); Student student =(Student) session.load(Student.class, 23); System.out.println("姓名:"+student.getStudentName()); for(Certificate c:student.getCertificates()){ System.out.println("编号:"+c.getCertificateNo()); } session.getTransaction().commit(); } catch (Exception e) { session.getTransaction().rollback(); e.printStackTrace(); } finally { HibernateUtil.closeSession(session); } }发出的SQL:
Hibernate: select student0_.student_id as student1_0_0_, student0_.student_name as student2_0_0_, student0_.age as age0_0_ from t_student student0_ where student0_.student_id=? 姓名:钱六 Hibernate: select certificat0_.student_id as student4_0_1_, certificat0_.certificate_id as certific1_1_, certificat0_.certificate_id as certific1_1_0_, certificat0_.certificate_name as certific2_1_0_, certificat0_.certificate_no as certific3_1_0_ from t_certificate certificat0_ where certificat0_.student_id=? 编号:3a10001 编号:3a10002
第二条查询语句用于查询关联对象,其实我们可以通过一条sql语句查询关联对象,如下:select * from t_student t1 inner join t_certificate t2 on t2.student_id=t1.student_id where t1.student_id=23;后面再进行优化
时间: 2024-10-23 12:49:08