Hibernate学习笔记（三）

一：班级学生一对多映射实现（双向）

Class类

public class Class {private int classId;private String className;private Set<Student>students=new HashSet<Student>();public Set<Student> getStudents() {return students;}public void setStudents(Set<Student> students) {this.students = students;}public int getClassId() {return classId;}public void setClassId(int classId) {this.classId = classId;}public String getClassName() {return className;}public void setClassName(String className) {this.className = className;}}

Class.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.zhu.model"><class name="Class" table="t_class"> <id name="classId" column="classId"> <generator class="native"></generator> </id> <property name="className"></property> <set name="students" cascade="save-update" inverse="true"> <key column="classId"></key> <one-to-many class="com.zhu.model.Student" /> </set></class></hibernate-mapping>

单元测试方法

@Testpublic void test() {Class c=new Class();c.setClassName("计科1501B");Student s1=new Student();s1.setName("张三");Student s2=new Student();s2.setName("李四");c.getStudents().add(s1);c.getStudents().add(s2);session.save(c);}

通过班级获取学生

@Testpublic void getStudentsByClass() {Class c=(Class)session.get(Class.class,1);for(Student s:c.getStudents()){System.out.println(s);}}

二：inverse 属性（inverse的作用是在hibernate中是通过inverse的设置来决定是由谁来维护表和表之间的关系的）

@Testpublic void testInverse() {Class c=(Class)session.get(Class.class,1);Student s=(Student)session.get(Student.class,Long.valueOf(1));s.setC(c);c.getStudents().add(s);}

三：级联删除

@Testpublic void testDelete() {Class c=(Class)session.get(Class.class,1);session.delete(c);}

级联删除需要设置 cascade="delete"属性，否则会抛出异常，因为不能删除有外键关联的主键的数据项

四：一对多双向自身关联关系映射

Node类

public class Node {private int id;private String nodeName;private Node parentNode;private Set<Node>childNodes=new HashSet<Node>();public int getId() {return id;}public void setId(int id) {this.id = id;}public String getNodeName() {return nodeName;}public void setNodeName(String nodeName) {this.nodeName = nodeName;}public Node getParentNode() {return parentNode;}public void setParentNode(Node parentNode) {this.parentNode = parentNode;}public Set<Node> getChildNodes() {return childNodes;}public void setChildNodes(Set<Node> childNodes) {this.childNodes = childNodes;}}

Node.hbm.xml

<?xml version="1.0"?><!DOCTYPE hibernate-mapping PUBLIC        "-//Hibernate/Hibernate Mapping DTD 3.0//EN"        "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd"><hibernate-mapping package="com.zhu.model"><class name="Node" table="t_node"> <id name="id"> <generator class="native"></generator> </id> <property name="nodeName"></property>  <set name="childNodes" cascade="save-update" inverse="true" > <key column="nodeId"></key> <one-to-many class="com.zhu.model.Node" /> </set> <many-to-one name="parentNode" column="nodeId" cascade="save-update"></many-to-one></class></hibernate-mapping>

@Testpublic void testSaveMenu() {Node root=new Node();root.setNodeName("根节点");Node node1=new Node();node1.setNodeName("子节点1");Node node2=new Node();node2.setNodeName("子节点2");node1.setParentNode(root);node2.setParentNode(root);session.save(node1);session.save(node2);}