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
1 @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 2 @Table(name="t_user") ----> 设置数据库的表名 3 public class User 4 { 5 ????private int id; 6 ????private String username; 7 ????private String password; 8 ????private Date born; 9 ????private Date registerDate;10 11 ????@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12 ????public Date getRegisterDate()13 ????{14 ????????return registerDate;15 ????}16 ????public void setRegisterDate(Date registerDate)17 ????{18 ????????this.registerDate = registerDate;19 ????}20 21 ????@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)22 ????@GeneratedValue ----> ID的生成策略为自动生成 23 ????public int getId()24 ????{25 ????????return id;26 ????}27 ????public void setId(int id)28 ????{29 ????????this.id = id;30 ????}31 ? ............32 }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.qinkang.bean.User"/><!-- 基于hbm.xml配置文件 --> ???????<mapping resource="com/qinkang/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：
1 @Entity 2 @Table(name="t_classroom") 3 public class ClassRoom 4 { 5 ????private int id; 6 ????private String className; 7 ????private Set<Student> students; 8 ?????9 ????public ClassRoom()10 ????{11 ????????students = new HashSet<Student>();12 ????}13 ????14 ????public void addStudent(Student student)15 ????{16 ????????students.add(student);17 ????}18 19 ????@Id20 ????@GeneratedValue21 ????public int getId()22 ????{23 ????????return id;24 ????}25 26 ????public void setId(int id)27 ????{28 ????????this.id = id;29 ????}30 31 ????public String getClassName()32 ????{33 ????????return className;34 ????}35 36 ????public void setClassName(String className)37 ????{38 ????????this.className = className;39 ????}40 41 ????@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)42 ????@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43 ????public Set<Student> getStudents()44 ????{45 ????????return students;46 ????}47 48 ????public void setStudents(Set<Student> students)49 ????{50 ????????this.students = students;51 ????}52 ????53 }Student类：
1 @Entity 2 @Table(name="t_student") 3 public class Student 4 { 5 ????private int id; 6 ????private String name; 7 ????private int age; 8 ????private ClassRoom room; 9 ????10 ????@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)11 ????@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)12 ????public ClassRoom getRoom()13 ????{14 ????????return room;15 ????}16 ????public void setRoom(ClassRoom room)17 ????{18 ????????this.room = room;19 ????}20 ????@Id21 ????@GeneratedValue22 ????public int getId()23 ????{24 ????????return id;25 ????}26 ????public void setId(int id)27 ????{28 ????????this.id = id;29 ????}30 ????public String getName()31 ????{32 ????????return name;33 ????}34 ????public void setName(String name)35 ????{36 ????????this.name = name;37 ????}38 ????public int getAge()39 ????{40 ????????return age;41 ????}42 ????public void setAge(int age)43 ????{44 ????????this.age = age;45 ????}46 ????47 }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：
1 @Entity 2 @Table(name="t_person") 3 public class Person 4 { 5 ????private int id; 6 ????private String name; 7 ????private IDCard card; 8 ?????9 ????@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10 ????public IDCard getCard()11 ????{12 ????????return card;13 ????}14 ????public void setCard(IDCard card)15 ????{16 ????????this.card = card;17 ????}18 ????@Id19 ????@GeneratedValue20 ????public int getId()21 ????{22 ????????return id;23 ????}24 ????public void setId(int id)25 ????{26 ????????this.id = id;27 ????}28 ????public String getName()29 ????{30 ????????return name;31 ????}32 ????public void setName(String name)33 ????{34 ????????this.name = name;35 ????}36 ????37 }IDCard类：
1 @Entity 2 @Table(name="t_id_card") 3 public class IDCard 4 { 5 ????private int id; 6 ????private String no; 7 ????private Person person; 8 ?????9 ????@Id10 ????@GeneratedValue11 ????public int getId()12 ????{13 ????????return id;14 ????}15 ????public void setId(int id)16 ????{17 ????????this.id = id;18 ????}19 ????public String getNo()20 ????{21 ????????return no;22 ????}23 ????public void setNo(String no)24 ????{25 ????????this.no = no;26 ????}27 ????@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28 ????@JoinColumn(name="pid") ---> 指定外键的名字 pid29 ????public Person getPerson()30 ????{31 ????????return person;32 ????}33 ????public void setPerson(Person person)34 ????{35 ????????this.person = person;36 ????}37 }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：
1 @Entity 2 @Table(name="t_teacher") 3 public class Teacher 4 { 5 ????private int id; 6 ????private String name; 7 ????private Set<Course> courses; 8 ?????9 ????public Teacher()10 ????{11 ????????courses = new HashSet<Course>();12 ????}13 ????public void addCourse(Course course)14 ????{15 ????????courses.add(course);16 ????}17 ????18 ????@Id19 ????@GeneratedValue20 ????public int getId()21 ????{22 ????????return id;23 ????}24 ????public void setId(int id)25 ????{26 ????????this.id = id;27 ????}28 ????public String getName()29 ????{30 ????????return name;31 ????}32 ????public void setName(String name)33 ????{34 ????????this.name = name;35 ????}36 ????@ManyToMany(mappedBy="teachers") ---> 表示由Course那一方来进行维护37 ????public Set<Course> getCourses()38 ????{39 ????????return courses;40 ????}41 ????public void setCourses(Set<Course> courses)42 ????{43 ????????this.courses = courses;44 ????}45 ????46 }Course类：
1 @Entity 2 @Table(name="t_course") 3 public class Course 4 { 5 ????private int id; 6 ????private String name; 7 ????private Set<Teacher> teachers; 8 ?????9 ????public Course()10 ????{11 ????????teachers = new HashSet<Teacher>();12 ????}13 ????public void addTeacher(Teacher teacher)14 ????{15 ????????teachers.add(teacher);16 ????}17 ????@ManyToMany ---> ManyToMany指定多对多的关联关系18 ????@JoinTable(name="t_teacher_course", joinColumns={ @JoinColumn(name="cid")}, 19 ????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 tid20 ????public Set<Teacher> getTeachers()21 ????{22 ????????return teachers;23 ????}24 25 ????public void setTeachers(Set<Teacher> teachers)26 ????{27 ????????this.teachers = teachers;28 ????}29 30 ????@Id31 ????@GeneratedValue32 ????public int getId()33 ????{34 ????????return id;35 ????}36 37 ????public void setId(int id)38 ????{39 ????????this.id = id;40 ????}41 42 ????public String getName()43 ????{44 ????????return name;45 ????}46 47 ????public void setName(String name)48 ????{49 ????????this.name = name;50 ????}51 52 }2.将Many-to-Many拆分成两个One-to-Many的映射(Admin、Role、AdminRole)
Admin类：
1 @Entity 2 @Table(name="t_admin") 3 public class Admin 4 { 5 ????private int id; 6 ????private String name; 7 ????private Set<AdminRole> ars; 8 ????public Admin() 9 ????{10 ????????ars = new HashSet<AdminRole>();11 ????}12 ????public void add(AdminRole ar)13 ????{14 ????????ars.add(ar);15 ????}16 ????@Id17 ????@GeneratedValue18 ????public int getId()19 ????{20 ????????return id;21 ????}22 ????public void setId(int id)23 ????{24 ????????this.id = id;25 ????}26 ????public String getName()27 ????{28 ????????return name;29 ????}30 ????public void setName(String name)31 ????{32 ????????this.name = name;33 ????}34 ????@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"35 ????@LazyCollection(LazyCollectionOption.EXTRA) 36 ????public Set<AdminRole> getArs()37 ????{38 ????????return ars;39 ????}40 ????public void setArs(Set<AdminRole> ars)41 ????{42 ????????this.ars = ars;43 ????}44 }Role类：
1 @Entity 2 @Table(name="t_role") 3 public class Role 4 { 5 ????private int id; 6 ????private String name; 7 ????private Set<AdminRole> ars; 8 ????public Role() 9 ????{10 ????????ars = new HashSet<AdminRole>();11 ????}12 ????public void add(AdminRole ar)13 ????{14 ????????ars.add(ar);15 ????}16 ????@Id17 ????@GeneratedValue18 ????public int getId()19 ????{20 ????????return id;21 ????}22 ????public void setId(int id)23 ????{24 ????????this.id = id;25 ????}26 ????public String getName()27 ????{28 ????????return name;29 ????}30 ????public void setName(String name)31 ????{32 ????????this.name = name;33 ????}34 ????@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"35 ????@LazyCollection(LazyCollectionOption.EXTRA)36 ????public Set<AdminRole> getArs()37 ????{38 ????????return ars;39 ????}40 ????public void setArs(Set<AdminRole> ars)41 ????{42 ????????this.ars = ars;43 ????}44 }AdminRole类：
1 @Entity 2 @Table(name="t_admin_role") 3 public class AdminRole 4 { 5 ????private int id; 6 ????private String name; 7 ????private Admin admin; 8 ????private Role role; 9 ????@Id10 ????@GeneratedValue11 ????public int getId()12 ????{13 ????????return id;14 ????}15 ????public void setId(int id)16 ????{17 ????????this.id = id;18 ????}19 ????public String getName()20 ????{21 ????????return name;22 ????}23 ????public void setName(String name)24 ????{25 ????????this.name = name;26 ????}27 ????@ManyToOne ---> ManyToOne关联到Admin28 ????@JoinColumn(name="aid") 29 ????public Admin getAdmin()30 ????{31 ????????return admin;32 ????}33 ????public void setAdmin(Admin admin)34 ????{35 ????????this.admin = admin;36 ????}37 ????@ManyToOne ---> 38 ????@JoinColumn(name="rid")39 ????public Role getRole()40 ????{41 ????????return role;42 ????}43 ????public void setRole(Role role)44 ????{45 ????????this.role = role;46 ????}47 }小提示：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
hibernate annotation注解方式来处理映射关系
原文地址：https://www.cnblogs.com/smellpawn/p/10798081.html