Hibernate的关系映射总结annotation版本

Hibernate关系一般分成这么几种情况：一对一单向，一对一双向，一对多单向，多对一单向，一对多双向，多对一双向，多对多单向，多对多双向。

1：一对一单向

@Entity
public class Husband {
		private int id;
		private String name;
		private Wife wife;
		@Id
		@GeneratedValue
		public int getId() {
			return id;
		}
		public String getName() {
			return name;
		}
		@OneToOne
		@JoinColumn(name="wife")//定义字段名称..
		public Wife getWife() {
			return wife;
		}
		public void setId(int id) {
			this.id = id;
		}
		public void setName(String name) {
			this.name = name;
		}
		public void setWife(Wife wife) {
			this.wife = wife;
		}
}

public class Wife {
		private int id;
		private String name;
		@Id
		@GeneratedValue
		public int getId() {
			return id;
		}
		public String getName() {
			return name;
		}
		public void setId(int id) {
			this.id = id;
		}
		public void setName(String name) {
			this.name = name;
		}
}

create table Husband (id integer not null auto_increment, name varchar(255), wife integer, primary key (id))
create table Wife (id integer not null auto_increment, name varchar(255), primary key (id))
alter table Husband add index FKAEEA401BAECA6750 (wife), add constraint FKAEEA401BAECA6750 foreign key(wife) references Wife (id)

2：一对一双向

public class Husband {
		private int id;
		private String name;
		private Wife wife;
		@Id
		@GeneratedValue
		public int getId() {
			return id;
		}
		public String getName() {
			return name;
		}
		@OneToOne
		@JoinColumn(name="wife")//定义字段名称..
		public Wife getWife() {
			return wife;
		}
		public void setId(int id) {
			this.id = id;
		}
		public void setName(String name) {
			this.name = name;
		}
		public void setWife(Wife wife) {
			this.wife = wife;
		}
}

public class Wife {
		private int id;
		private String name;
		private Husband husband;
		@OneToOne(mappedBy="wife")
		//双向外键关联需要设置mappedBy，否则会有冗余
		//其中"wife"为Husband的get方法中的wife，还不是那个wife字段。
		
		public Husband getHusband() {
			return husband;
		}
		public void setHusband(Husband husband) {
			this.husband = husband;
		}
		@Id
		@GeneratedValue
		public int getId() {
			return id;
		}
		public String getName() {
			return name;
		}
		public void setId(int id) {
			this.id = id;
		}
		public void setName(String name) {
			this.name = name;
		}
}

不要忘了mappedBy，否则会生成两个外键关联。

其实单向和双向生成的表没什么区别，区别只是单向的时候只能由一方获得另外一方，而双向则是每一方都能获得对方。

create table Husband (id integer not null auto_increment, name varchar(255), wife integer, primary key (id))
create table Wife (id integer not null auto_increment, name varchar(255), primary key (id))
alter table Husband add index FKAEEA401BAECA6750 (wife), add constraint FKAEEA401BAECA6750 foreign key (wife) references Wife (id)

3：多对一

@Entity
@Table(name="t_group")
public class Group {
	private int id;
	private String name;
	@Id
	@GeneratedValue
	@Column(name="group_id")
	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;
	}
}

 

@Table(name="t_user")
public class User {
	private int id;
	private String name;
	private Group group;
	@ManyToOne
	@JoinColumn(name="id_group")
	public Group getGroup() {
		return group;
	}
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	public void setGroup(Group group) {
		this.group = group;
	}
	public void setId(int id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
}

多对一外键关联的表设计是把一那一方的id放在多的那一方表中，如果反过来则会产生冗余。

create table t_group (group_id integer not null auto_increment, name varchar(255), primary key (group_id))
create table t_user (id integer not null auto_increment, name varchar(255), id_group integer, primary key (id))
alter table t_user add index FKCB63CCB6102EF96C (id_group), add constraint FKCB63CCB6102EF96C foreign key (id_group) references t_group (group_id)

 

4：一对多

@Table(name="t_group")

public class Group {
	private int id;
	private String name;
	private Set<User> users;
	@Id
	@GeneratedValue
	@Column(name="group_id")
	public int getId() {
		return id;
	}
	@OneToMany
	@JoinColumn(name="group_id")
	//不要忘了joinColumn,否则会认为是多对多的一种，会生成一张中间表.
	public Set<User> getUsers() {
		return users;
	}
	public void setUsers(Set<User> users) {
		this.users = users;
	}
	public void setId(int id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

@Table(name="t_user")
public class User {
	private int id;
	private String name;

	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	
	public void setId(int id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
}

create table t_group (group_id integer not null auto_increment, name varchar(255), primary key (group_id))
create table t_user (id integer not null auto_increment, name varchar(255), group_id integer, primary key (id))
alter table t_user add index FKCB63CCB6411589EC (group_id), add constraint FKCB63CCB6411589EC foreign key (group_id) references t_group (group_id)

如果没有@JoinColumn(name="group_id")，那么会怎么样呢？

create table t_group (group_id integer not null auto_increment, name varchar(255), primary key (group_id))
create table t_group_t_user (t_group_group_id integer not null, users_id integer not null, primary key (t_group_group_id, users_id), unique (users_id))
create table t_user (id integer not null auto_increment, name varchar(255), primary key (id))
alter table t_group_t_user add index FKCFE61C612E429AD7 (t_group_group_id), add constraint FKCFE61C612E429AD7 foreign key (t_group_group_id) references t_group (group_id)
alter table t_group_t_user add index FKCFE61C619EBDBBAB (users_id), add constraint FKCFE61C619EBDBBAB foreign key (users_id) references t_user (id)

它会生成一张中间表。当作是多对多。

5：多对多单向

public class Teacher {
	private int id;
	private String name;
	private Set<Student> students;
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	@ManyToMany
	@JoinTable(
			name="t_s",
			joinColumns={
					@JoinColumn(name="teacherId")},
			inverseJoinColumns={@JoinColumn(name="studentId")}	
	)
	//如果不加@JoinTable,那么中间关系表属性就是teachersidd, studentsid。而JoinTable就是为了改变这个名称的。
	public Set<Student> getStudents() {
		return students;
	}
	public void setId(int id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
	public void setStudents(Set<Student> students) {
		this.students = students;
	}
}

 

public class Student {
	private int id ;
	private String name;
	
	@Id
	@GeneratedValue
	public int getId() {
		return id;
	}
	public String getName() {
		return name;
	}
	
	
	public void setId(int id) {
		this.id = id;
	}
	public void setName(String name) {
		this.name = name;
	}
	
}

 

create table Student (id integer not null auto_increment, name varchar(255), primary key (id))
create table Teacher (id integer not null auto_increment, name varchar(255), primary key (id))
create table t_s (teacherId integer not null, studentId integer not null, primary key (teacherId, studentId))
alter table t_s add index FK1BF6883117471 (teacherId), add constraint FK1BF6883117471 foreign key (teacherId) references Teacher (id)
alter table t_s add index FK1BF68E56AEE3 (studentId), add constraint FK1BF68E56AEE3 foreign key (studentId) references Student (id)

如果不加@JoinTable，其实也没关系。结果如下：

create table Student (id integer not null auto_increment, name varchar(255), primary key (id))
create table Teacher (id integer not null auto_increment, name varchar(255), primary key (id))
create table Teacher_Student (Teacher_id integer not null, students_id integer not null, primary key (Teacher_id, students_id))
alter table Teacher_Student add index FK55FA429E1052676F (students_id), add constraint FK55FA429E1052676F foreign key (students_id) references Student (id)
alter table Teacher_Student add index FK55FA429E57018E8C (Teacher_id), add constraint FK55FA429E57018E8C foreign key (Teacher_id) references Teacher (id)

差别并不是很明显，只是一个名称上的区别：students_id(我们想象应该是student_id)和studentId（我们自定义的)。

其实还有几种没写，全是双向的，我只是写出了一对一的双向，其他的也差不多。