一、常用关系
依赖关系
如果A对象离开了B对象，A对象就不能正常编译，则A对象依赖B对象
class B{}
class A{
//在A类中使用到了B.
B b;//依赖情况1
public void doWok(B b)//依赖情况2
{
B bb;//依赖情况3
}
}
关联关系
A对象依赖B对象，并且把B对象作为A对象的一个属性，则A和B是关联关系，关联关系是一种特殊的依赖关系
聚合关系
表示整体和部分的关系，整体和部分之间可以相互独立存在，一定是有两个模块来分别管理整体和部分
组合关系（强聚合关系）
是整体和部分不能独立存在，一定是在一个模块中同时管理整体和部分，生命周期必须相同，如：订单和订单明细
二、多重性
一对一
一个A对象属于一个B对象，一个B对象属于一个A对象。比如：每一个人有一个唯一的省份证号
- Person
package com.revanwang._02.relation.one2one;
import lombok.Data;
@Data
public class Person {
private IDNumber idNumber;
}
- IDNumber
package com.revanwang._02.relation.one2one;
import lombok.Data;
@Data
public class IDNumber {
private Person person;
}
- testOne2One
public void testOne2One() {
Person person = new Person();
IDNumber idNumber = new IDNumber();
person.setIdNumber(idNumber);
idNumber.setPerson(person);
}
一对多
一个A对象包含多个B对象（一个部门有多个员工）
- Department
package com.revanwang._02.relation.one2many;
import lombok.Getter;
import lombok.Setter;
import java.util.List;
public class Department {
@Setter
@Getter
private List<Employee> employeeList = new ArrayList<>();
}
- Employee
package com.revanwang._02.relation.one2many;
public class Employee {
}
- testOne2Many
public void testOne2Many() {
Department depart = new Department();
Employee e1 = new Employee();
Employee e2 = new Employee();
Employee e3 = new Employee();
depart.getEmployeeList().add(e1);
depart.getEmployeeList().add(e2);
depart.getEmployeeList().add(e3);
}
多对一
多个A对象属于一个B对象，并且每个A对象只能属于一个B对象（Employee 和 Department）
- Employee
package com.revanwang._02.relation.many2one;
public class Employee {
private Department department;
}
- Department
package com.revanwang._02.relation.many2one;
public class Department {
}
- testMany2One
public void testMany2One() {
Department department = new Department();
Employee e1 = new Employee();
Employee e2 = new Employee();
e1.setDepartment(department);
e2.setDepartment(department);
}
多对多
一个A对象属于多个B对象,一个B对象属于多个A对象.
- Teacher
package com.revanwang._02.relation.many2many;
import lombok.Data;
import java.util.ArrayList;
import java.util.List;
@Data
public class Teacher {
private List<Student> studentList = new ArrayList<>();
}
- Student
package com.revanwang._02.relation.many2many;
import lombok.Data;
import java.util.ArrayList;
import java.util.List;
@Data
public class Student {
private List<Teacher> teacherList = new ArrayList<>();
}
- testMany2Many
public void testMany2Many() {
Teacher t1 = new Teacher();
Teacher t2 = new Teacher();
Student s1 = new Student();
Student s2 = new Student();
s1.getTeacherList().add(t1);
s1.getTeacherList().add(t2);
t1.getStudentList().add(s1);
t1.getStudentList().add(s2);
}
三、导航性
如果通过A对象中的某一个属性可以访问该属性对应的B对象,则说A可以导航到B.
- 1).单向:只能从A通过属性导航到B,B不能导航到A.
- 2).双向:A可以通过属性导航到B,B也可以通过属性导航到A.
判断方法:
1,判断都是从对象的实例上面来看的;
2,判断关系必须确定一对属性;
3,判断关系必须确定具体需求;
四、集合映射
4.1、Set映射
- Person
package com.revanwang._03.collection.set;
import lombok.Data;
import java.util.HashSet;
import java.util.Set;
@Data
public class Person {
private Long id;
private String name;
private Set<String> hobbySet = new HashSet<>();
}
- Person.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.revanwang._03.collection.set">
<class name="Person" table="t_person">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"/>
<!-- Set集合设置 -->
<set name="hobbySet" table="person_hobby_set">
<key column="p_id"></key>
<element column="hobby" type="java.lang.String"/>
</set>
</class>
</hibernate-mapping>
- testSet
public void testSet() {
Person person = new Person();
person.setName("乔峰");
person.getHobbySet().add("喝酒");
person.getHobbySet().add("天龙八部");
person.getHobbySet().add("北乔峰");
Session session = HibernateUtil.getHibernateSession();
session.beginTransaction();
session.persist(person);
session.getTransaction().commit();
}
t_person表.png
set表.png
4.2、List映射
- Person
package com.revanwang._03.collection.list;
import lombok.Data;
import java.util.ArrayList;
import java.util.List;
@Data
public class Person {
private Long id;
private String name;
private List<String> hobbyList = new ArrayList<>();
}
- Person.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.revanwang._03.collection.list">
<class name="Person" table="t_person">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"/>
<!-- List集合设置 -->
<list name="hobbyList" table="person_hobby">
<key column="p_id"></key>
<index column="ind" type="integer"/>
<element column="hobby" type="java.lang.String"/>
</list>
</class>
</hibernate-mapping>
4.3、Bag映射
- Person
package com.revanwang._03.collection.bag;
import lombok.Data;
import java.util.ArrayList;
import java.util.List;
@Data
public class Person {
private Long id;
private String name;
private List<String> hobbyList = new ArrayList<>();
}
- Person.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.revanwang._03.collection.bag">
<class name="Person" table="t_person">
<id name="id" column="id">
<generator class="native"></generator>
</id>
<property name="name" column="name"/>
<!-- Bag集合设置 -->
<bag name="hobbyList" table="t_person_bag">
<key column="p_id"></key>
<element column="hobby" type="java.lang.String"/>
</bag>
</class>
</hibernate-mapping>
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