转自:hibernate annotation注解方式来处理映射关系
在hibernate中，通常配置对象关系映射关系有两种，一种是基于xml的方式，另一种是基于annotation的注解方式，熟话说，萝卜青菜，可有所爱，每个人都有自己喜欢的配置方式，我在试了这两种方式以后，发现使用annotation的方式可以更简介，所以这里就简单记录下通过annotation来配置各种映射关系，在hibernate4以后已经将annotation的jar包集成进来了，如果使用hibernate3的版本就需要引入annotation的jar包。
一、单对象操作
@Entity ---> 如果我们当前这个bean要设置成实体对象，就需要加上Entity这个注解@Table(name="t_user") ----> 设置数据库的表名public class User{ ???private int id; ???private String username; ???private String password; ???private Date born; ???private Date registerDate;
???@Column(name="register_date") ---> Column中的name属性对应了数据库的该字段名字，里面还有其他属性，例如length，nullable等等 ???public Date getRegisterDate() ???{ ???????return registerDate; ???} ???public void setRegisterDate(Date registerDate) ???{ ???????this.registerDate = registerDate; ???}
???@Id ---> 定义为数据库的主键ID (建议不要在属性上引入注解，因为属性是private的，如果引入注解会破坏其封装特性，所以建议在getter方法上加入注解) ???@GeneratedValue ----> ID的生成策略为自动生成 ???public int getId() ???{ ???????return id; ???} ???public void setId(int id) ???{ ???????this.id = id; ???} ............}最后只需要在hibernate.cfg.xml文件里面将该实体类加进去即可：
<!-- 基于annotation的配置 --> ???????<mapping class="com.xiaoluo.bean.User"/><!-- 基于hbm.xml配置文件 --> ???????<mapping resource="com/xiaoluo/bean/User.hbm.xml"/>
这样我们就可以写测试类来进行我们的CRUD操作了。
二、一对多的映射(one-to-many)
这里我们定义了两个实体类，一个是ClassRoom，一个是Student，这两者是一对多的关联关系。
ClassRoom类：
@Entity@Table(name="t_classroom")public class ClassRoom{ ???private int id; ???private String className; ???private Set<Student> students; ???????public ClassRoom() ???{ ???????students = new HashSet<Student>(); ???} ???????public void addStudent(Student student) ???{ ???????students.add(student); ???} ???@Id ???@GeneratedValue ???public int getId() ???{ ???????return id; ???} ???public void setId(int id) ???{ ???????this.id = id; ???} ???public String getClassName() ???{ ???????return className; ???} ???public void setClassName(String className) ???{ ???????this.className = className; ???} ???@OneToMany(mappedBy="room") ---> OneToMany指定了一对多的关系，mappedBy="room"指定了由多的那一方来维护关联关系，mappedBy指的是多的一方对1的这一方的依赖的属性，(注意：如果没有指定由谁来维护关联关系，则系统会给我们创建一张中间表) ???@LazyCollection(LazyCollectionOption.EXTRA) ---> LazyCollection属性设置成EXTRA指定了当如果查询数据的个数时候，只会发出一条 count(*)的语句，提高性能 ???public Set<Student> getStudents() ???{ ???????return students; ???} ???public void setStudents(Set<Student> students) ???{ ???????this.students = students; ???} ???}Student类：
@Entity@Table(name="t_student")public class Student{ ???private int id; ???private String name; ???private int age; ???private ClassRoom room; ???????@ManyToOne(fetch=FetchType.LAZY) ---> ManyToOne指定了多对一的关系，fetch=FetchType.LAZY属性表示在多的那一方通过延迟加载的方式加载对象(默认不是延迟加载) ???@JoinColumn(name="rid") ---> 通过 JoinColumn 的name属性指定了外键的名称 rid (注意：如果我们不通过JoinColum来指定外键的名称，系统会给我们声明一个名称) ???public ClassRoom getRoom() ???{ ???????return room; ???} ???public void setRoom(ClassRoom room) ???{ ???????this.room = room; ???} ???@Id ???@GeneratedValue ???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 int getAge() ???{ ???????return age; ???} ???public void setAge(int age) ???{ ???????this.age = age; ???} ???}三、一对一映射(One-to-One)
一对一关系这里定义了一个Person对象以及一个IDCard对象
Person类：
@Entity@Table(name="t_person")public class Person{ ???private int id; ???private String name; ???private IDCard card; ???????@OneToOne(mappedBy="person") ---> 指定了OneToOne的关联关系，mappedBy同样指定由对方来进行维护关联关系 ???public IDCard getCard() ???{ ???????return card; ???} ???public void setCard(IDCard card) ???{ ???????this.card = card; ???} ???@Id ???@GeneratedValue ???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; ???} ???}IDCard类：
@Entity@Table(name="t_id_card")public class IDCard{ ???private int id; ???private String no; ???private Person person; ???????@Id ???@GeneratedValue ???public int getId() ???{ ???????return id; ???} ???public void setId(int id) ???{ ???????this.id = id; ???} ???public String getNo() ???{ ???????return no; ???} ???public void setNo(String no) ???{ ???????this.no = no; ???} ???@OneToOne ---> OnetoOne指定了一对一的关联关系，一对一中随便指定一方来维护映射关系，这里选择IDCard来进行维护 ???@JoinColumn(name="pid") ---> 指定外键的名字 pid ???public Person getPerson() ???{ ???????return person; ???} ???public void setPerson(Person person) ???{ ???????this.person = person; ???}}注意:在判断到底是谁维护关联关系时，可以通过查看外键，哪个实体类定义了外键，哪个类就负责维护关联关系。
四、Many-to-Many映射(多对多映射关系)
多对多这里通常有两种处理方式，一种是通过建立一张中间表，然后由任一一个多的一方来维护关联关系，另一种就是将多对多拆分成两个一对多的关联关系
1.通过中间表由任一一个多的一方来维护关联关系
Teacher类：
@Entity@Table(name="t_teacher")public class Teacher{ ???private int id; ???private String name; ???private Set<Course> courses; ???????public Teacher() ???{ ???????courses = new HashSet<Course>(); ???} ???public void addCourse(Course course) ???{ ???????courses.add(course); ???} ???????@Id ???@GeneratedValue ???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; ???} ???@ManyToMany(mappedBy="teachers") ---> 表示由Course那一方来进行维护 ???public Set<Course> getCourses() ???{ ???????return courses; ???} ???public void setCourses(Set<Course> courses) ???{ ???????this.courses = courses; ???} ???}Course类：
@Entity@Table(name="t_course")public class Course{ ???private int id; ???private String name; ???private Set<Teacher> teachers; ???????public Course() ???{ ???????teachers = new HashSet<Teacher>(); ???} ???public void addTeacher(Teacher teacher) ???{ ???????teachers.add(teacher); ???} ???@ManyToMany ---> ManyToMany指定多对多的关联关系 ???@JoinTable(name="t_teacher_course", joinColumns={ @JoinColumn(name="cid")}, ????inverseJoinColumns={ @JoinColumn(name = "tid") }) ---> 因为多对多之间会通过一张中间表来维护两表直接的关系，所以通过 JoinTable 这个注解来声明，name就是指定了中间表的名字，JoinColumns是一个 @JoinColumn类型的数组，表示的是我这方在对方中的外键名称，我方是Course，所以在对方外键的名称就是 rid，inverseJoinColumns也是一个 @JoinColumn类型的数组，表示的是对方在我这放中的外键名称，对方是Teacher，所以在我方外键的名称就是 tid ???public Set<Teacher> getTeachers() ???{ ???????return teachers; ???} ???public void setTeachers(Set<Teacher> teachers) ???{ ???????this.teachers = teachers; ???} ???@Id ???@GeneratedValue ???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; ???}}2.将Many-to-Many拆分成两个One-to-Many的映射(Admin、Role、AdminRole)
Admin类：
@Entity@Table(name="t_admin")public class Admin{ ???private int id; ???private String name; ???private Set<AdminRole> ars; ???public Admin() ???{ ???????ars = new HashSet<AdminRole>(); ???} ???public void add(AdminRole ar) ???{ ???????ars.add(ar); ???} ???@Id ???@GeneratedValue ???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; ???} ???@OneToMany(mappedBy="admin") ---> OneToMany关联到了AdminRole这个类，由AdminRole这个类来维护多对一的关系，mappedBy="admin" ???@LazyCollection(LazyCollectionOption.EXTRA) ???public Set<AdminRole> getArs() ???{ ???????return ars; ???} ???public void setArs(Set<AdminRole> ars) ???{ ???????this.ars = ars; ???}}Role类：
@Entity@Table(name="t_role")public class Role{ ???private int id; ???private String name; ???private Set<AdminRole> ars; ???public Role() ???{ ???????ars = new HashSet<AdminRole>(); ???} ???public void add(AdminRole ar) ???{ ???????ars.add(ar); ???} ???@Id ???@GeneratedValue ???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; ???} ???@OneToMany(mappedBy="role") ---> OneToMany指定了由AdminRole这个类来维护多对一的关联关系，mappedBy="role" ???@LazyCollection(LazyCollectionOption.EXTRA) ???public Set<AdminRole> getArs() ???{ ???????return ars; ???} ???public void setArs(Set<AdminRole> ars) ???{ ???????this.ars = ars; ???}}AdminRole类：
@Entity@Table(name="t_admin_role")public class AdminRole{ ???private int id; ???private String name; ???private Admin admin; ???private Role role; ???@Id ???@GeneratedValue ???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; ???} ???@ManyToOne ---> ManyToOne关联到Admin ???@JoinColumn(name="aid") ???public Admin getAdmin() ???{ ???????return admin; ???} ???public void setAdmin(Admin admin) ???{ ???????this.admin = admin; ???} ???@ManyToOne ---> ???@JoinColumn(name="rid") ???public Role getRole() ???{ ???????return role; ???} ???public void setRole(Role role) ???{ ???????this.role = role; ???}}小技巧:通过hibernate来进行插入操作的时候，不管是一对多、一对一还是多对多，都只需要记住一点，在哪个实体类声明了外键，就由哪个类来维护关系，在保存数据时，总是先保存的是没有维护关联关系的那一方的数据，后保存维护了关联关系的那一方的数据，如：
Person p = new Person(); ???????????p.setName("xiaoluo"); ???????????session.save(p); ???????????????????????IDCard card = new IDCard(); ???????????card.setNo("1111111111"); ???????????card.setPerson(p); ???????????session.save(card);以上就是对hibernate annotation注解方式来配置映射关系的一些总结。
hibernate关联映射注解
原文地址：https://www.cnblogs.com/yadongliang/p/8965091.html