疯狂

onetoone:单向

1,主键关联：

 在关联放使用@OneToOne

sql语句：（类代码见同前面的代码）

create table A (id integer not null auto_increment, aname varchar(255), b_id integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id))
alter table A add index FK41FCD34905 (b_id), add constraint FK41FCD34905 foreign key (b_id) references B (id)

可以使用@PrimaryKeyJoinColumn进行关联

2 双向：

在关联方使用 

@OneToOne(cascade=CascadeType.ALL)
@JoinColumn(name="b")

被关联方使用

@OneToOne(mappedBy="b")

最终sql：

create table A (id integer not null auto_increment, aname varchar(255), b integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id))
alter table A add index FK41FCA54B4F (b), add constraint FK41FCA54B4F foreign key (b) references B (id)

如果不写

@OneToOne(mappedBy="b")则会在被关联放也生成一个字段

最终代码:

create table A (id integer not null auto_increment, aname varchar(255), i_id integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), a_id integer, primary key (id))
alter table A add index FK41FCD6779E (i_id), add constraint FK41FCD6779E foreign key (i_id) references B (id)
alter table B add index FK42FCD2D4A5 (a_id), add constraint FK42FCD2D4A5 foreign key (a_id) references A (id)

  如果没有写@JoinColumn(name="b")则默认是关联属性名+下划线+id

最终sql：

create table A (id integer not null auto_increment, aname varchar(255), b_id integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id))
alter table A add index FK41FCD34905 (b_id), add constraint FK41FCD34905 foreign key (b_id) references B (id)

 可以使用@JoinColumn(referencedColumnName="bname")让主关联方不关联被关联放的主键

最终sql

Java代码

1. create table A (id integer not null auto_increment, aname varchar(255), b_bname varchar(255), primary key (id))   
2. create table B (id integer not null auto_increment, bname varchar(255), primary key (id), unique (bname))   
3. alter table A add index FK41E47CD6BD (b_bname), add constraint FK41E47CD6BD foreign key (b_bname) references B (bname)  

create table A (id integer not null auto_increment, aname varchar(255), b_bname varchar(255), primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id), unique (bname))
alter table A add index FK41E47CD6BD (b_bname), add constraint FK41E47CD6BD foreign key (b_bname) references B (bname)

  3 关联表

 使用

@OneToOne(cascade=CascadeType.ALL)
 @JoinTable(name="centert",joinColumns=@JoinColumn(name="aid"),inverseJoinColumns=@JoinColumn(name="bid"))

最终sql：

manytoone

和onetoone很相似

特殊情况：果不写：mappedBy这会产生中间表：

create table A (id integer not null auto_increment, aname varchar(255), i_id integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id))
create table B_A (B_id integer not null, a_id integer not null, unique (a_id))
alter table A add index FK41FCD6779E (i_id), add constraint FK41FCD6779E foreign key (i_id) references B (id)
alter table B_A add index FK10384FCD34905 (B_id), add constraint FK10384FCD34905 foreign key (B_id) references B (id)
alter table B_A add index FK10384FCD2D4A5 (a_id), add constraint FK10384FCD2D4A5 foreign key (a_id) references A (id)

 如

targetEntity属性可以关联接口

例如接口代码

public interface I {
}

 class B implments I

关联方：

private I i;
@ManyToOne(targetEntity=B.class)
public I getI() {
return i;
}

最终sql：

create table A (id integer not null auto_increment, aname varchar(255), i_id integer, primary key (id))
create table B (id integer not null auto_increment, bname varchar(255), primary key (id))
alter table A add index FK41FCD6779E (i_id), add constraint FK41FCD6779E foreign key (i_id) references B (id)