关联映射
多对一(Employee - Department)
一对多(Department-Employee)
一对一(Person - IDCard)
多对多(teacher - student)
组件映射(User-Name)
集合映射(set, list, map, bag)
inverse和cascade(Employee – Department)
多对一(Employee - Department)
映射文件<many-to-one name=”depart” column=”depart_id”/>
ER图
举例：
Department.java
package com.dzq.domain;import java.io.Serializable;import java.util.Set;public class Department implements Serializable{ private int id; private String name; private Set empls; 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 Set getEmpls() { return empls; } public void setEmpls(Set empls) { this.empls = empls; } }
Employee.java
package com.dzq.domain;import java.io.Serializable;public class Employee implements Serializable{ 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.hbm.xml
Employee.hbm.xml
测试代码：
public static void addEmAndDe(){ Employee em=new Employee(); Department depart=new Department(); depart.setName("FBI"); em.setDepart(depart); em.setName("AK47"); HibernateUntils.add(depart); HibernateUntils.add(em); }
一对多(Department-Employee)
一对一(Person - IdCard)
1)基于主键的one-to-one(person的映射文件)
idCard
例子：
Person.java 主对象
package com.dzq.domain;import java.io.Serializable;public class Person implements Serializable{ private int id; private String name; private IDCard idcard; 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 IDCard getIdcard() { return idcard; } public void setIdcard(IDCard idcard) { this.idcard = idcard; }} IDCard.java 从对象
package com.dzq.domain;import java.io.Serializable;public class IDCard implements Serializable{ private int id; private String name; private Person person; 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 Person getPerson() { return person; } public void setPerson(Person person) { this.person = person; }} IDCard.hbm.xml
person
Person.hbm.xml
测试代码：
OneToOne.java
package com.dzq.test;import org.hibernate.Session;import org.hibernate.Transaction;import com.dzq.domain.IDCard;import com.dzq.domain.Person;import com.dzq.utils.HibernateUntils;public class OneToOne { public static void main(String[] args) { add(); queryPerson(1); queryIDcard(1); } public static Person add(){ Session s=null; Transaction ts=null; try { s=HibernateUntils.getSession(); Person p=new Person(); IDCard idcard=new IDCard(); idcard.setName("0606"); p.setName("ll"); p.setIdcard(idcard); idcard.setPerson(p); ts=s.beginTransaction(); s.save(p); s.save(idcard); ts.commit(); return p; } catch (Exception e) { if(ts!=null) ts.rollback(); throw new RuntimeException(e); }finally{ if(s!=null){ s.close(); } } } /** * 查询主对象，用连接表查询 * @param id * @return */ public static Person queryPerson(int id){ Session s=null; try { s=HibernateUntils.getSession(); Person p=(Person) s.get(Person.class, id); System.out.println(p.getIdcard().getName()); return p; } finally{ if(s!=null){ s.close(); } } } /** * 查询从对象,查询两次 * @param id * @return */ public static IDCard queryIDcard(int id){ Session s=null; try { s=HibernateUntils.getSession(); IDCard idc= (IDCard) s.get(IDCard.class, id); System.out.println(idc.getPerson().getName()); return idc; } finally{ if(s!=null){ s.close(); } } }}
2)基于外健的one-to-one，可以描述为多对一，加unique=“true”约束
多对多(teacher - student)
在操作和性能方面都不太理想，所以多对多的映射使用较少，实际使用中最好转换成一对多的对象模型；Hibernate会为我们创建中间关联表，转换成两个一对多。
<set name="teacher" table="teacher_student">
<key column="teacher_id"/>
<many-to-many class="Student" column="student_id"/>
</set>
l 
package com.dzq.test;import java.util.HashSet;import java.util.Set;import org.hibernate.Session;import org.hibernate.Transaction;import com.dzq.domain.Student;import com.dzq.domain.Teacher;import com.dzq.utils.HibernateUntils;public class ManyToMany { public static void main(String[] args) { add(); query(1); } public static void add(){ Session s=null; Transaction ts=null; try { Set tes=new HashSet (); Set stus=new HashSet (); s=HibernateUntils.getSession(); Teacher t1=new Teacher(); t1.setName("gao"); Teacher t2=new Teacher(); t2.setName("gaoji"); tes.add(t1); tes.add(t2); Student s1=new Student(); s1.setName("hu"); Student s2=new Student(); s2.setName("xiaohu"); stus.add(s1); stus.add(s2); t1.setStudents(stus); t2.setStudents(stus); /*s1.setTeachers(tes); s2.setTeachers(tes);*/ // 会报错,插入重复，要一个就行 ts=s.beginTransaction(); s.save(t1); s.save(t2); s.save(s1); s.save(s2); ts.commit(); } catch (Exception e) { if(ts!=null) ts.rollback(); throw new RuntimeException(e); }finally{ if(s!=null){ s.close(); } } } /** * 多对多查询，效率很低，用的比较少，最好使用分页查询，数据量很小才会使用，数据大量是会存在很严重的性能问题 * @param id */ public static void query(int id){ Session s=null; try { s=HibernateUntils.getSession(); Teacher teacher=(Teacher) s.get(Teacher.class, id); System.out.println(teacher.getStudents().size()); } finally{ if(s!=null){ s.close(); } } } } 组件映射(User-Name)
关联的属性是个复杂类型的持久化类，但不是实体即：数据库中没有表与该属性对应，但该类的属性要之久保存的。
当组件的属性不能和表中的字段简单对应的时候可以选择实现：
org.hibernate.usertype. UserType或
org.hibernate.usertype. CompositeUserType
package com.dzq.domain;public class Name { private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; }} 只会产生一张表
关联关系的级联操作
package com.dzq.test;import java.util.HashSet;import java.util.Set;import org.hibernate.Hibernate;import org.hibernate.Session;import org.hibernate.Transaction;import com.dzq.domain.Department;import com.dzq.domain.Employee;import com.dzq.utils.HibernateUntils;public class ManyToOne { public static void main(String[] args) { add(); } public static void addEmAndDe(){ Employee em=new Employee(); Department depart=new Department(); depart.setName("FBI"); em.setDepart(depart); em.setName("AK47"); HibernateUntils.add(depart); HibernateUntils.add(em); } public static void add(){ Session s=null; Transaction ts=null; try { Department dep=new Department(); dep.setName("FBI"); Employee e1=new Employee(); Employee e2=new Employee(); e1.setName("hi"); e1.setDepart(dep); e2.setName("hello"); e2.setDepart(dep); Set empls=new HashSet (); empls.add(e1); empls.add(e2); dep.setEmpls(empls); s=HibernateUntils.getSession(); ts=s.beginTransaction(); //s.save(e1); //s.save(e2); s.save(dep); ts.commit(); } catch (Exception e) { ts.rollback(); throw new RuntimeException(e); }finally{ if(s!=null){ s.close(); } } } }