hibernate注解（一）JoinColumn

@Entity
@Table(name="t_group")
public class Group {
    private int id;
    private String name;
    
    public Group(){
        
    }
    public Group(String name) {
        this.name = name;
    }
    @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;
    }
}

@Entity
@Table(name="t_user")
public class User {
    private int id;
    private String name;
    private Group group;
    
    public User(){
        
    }
    public User(String name) {
        this.name = name;
    }
    @ManyToOne　　　　　　　　　　　　　　//Group不是数据库中的数据类型，所以要用ManyToOne转换
    @JoinColumn(name="mygroudid")     //在t_user表中生成mygroupid字段
    public Group getGroup() {
        return group;
    }
    public void setGroup(Group group) {
        this.group = group;
    }
    @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.生成的sql语句：

create table t_group (

　　id integer not null auto_increment,

　　name varchar(255),

　　primary key (id)

)
create table t_user (

　　id integer not null auto_increment,

　　name varchar(255),

　　mygroudid integer,

　　primary key (id)

)
alter table t_user add index FKCB63CCB6C650D60F (mygroudid), add constraint FKCB63CCB6C650D60F foreign key (mygroudid) references t_group (id)

2.如果不指定JoinColumn，也会生成默认的字段

create table t_group (id integer not null auto_increment, name varchar(255), primary key (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 FKCB63CCB69870A148 (group_id), add constraint FKCB63CCB69870A148 foreign key (group_id) references t_group (id)