一对一,各种形式的单双向关联.doc

共六种情况，分成两大类，每类有3个第一类: 1对1单向关联一对一，通过外健实现的单向关联是M:1的特例假设一个人只有一个办公室：Person(pid int primary key, pname char(10), office_id int references office(id);Office(oid int primary key, address char(10);CREATE TABLE person ( pid int(11) NOT NULL DEFAULT 0, pname char(10) DEFAULT NULL, office_id int(11) DEFAULT NULL, PRIMARY KEY (pid), KEY person_office_FK (office_id), CONSTRAINT person_office_FK FOREIGN KEY (office_id) REFERENCES office (oid);CREATE TABLE office ( oid int(11) NOT NULL DEFAULT 0, address varchar(20) DEFAULT NULL, PRIMARY KEY (oid)对应的类：public class Person private Integer pid;/主键private String pname;private Office office;/对应的办公室，单向关联public Integer getPid() return pid;public void setPid(Integer pid) this.pid = pid;public String getPname() return pname;public void setPname(String pname) this.pname = pname;public Office getOffice() return office;public void setOffice(Office office) this.office = office;OFFICE类：public class Office private Integer oid;/Office id为主键private String address;public Integer getOid() return oid;public void setOid(Integer oid) this.oid = oid;public String getAddress() return address;public void setAddress(String address) this.address = address;相应的映射文件：Person.hbm.xml Office.hbm.xml 测试:public static void main(String args) Session session = HibernateSessionFactory.getSession();Transaction tx = session.beginTransaction();Person p = new Person();p.setPname(张三);Office o = new Office();o.setAddress(北京);p.setOffice(o);/保存的顺序与效率有关session.save(o);session.save(p);mit();session.close();一对一，通过主健实现的单向关联主健类不能主健生成策略,由关联类负责.假设一个人只有一个办公室：Person(pid int primary key references office(oid), pname char(10);/注意pid既是主健也是外键Office(oid int primary key, address char(10);CREATE TABLE office ( oid int(11) NOT NULL DEFAULT 0, address varchar(20) DEFAULT NULL, PRIMARY KEY (oid)CREATE TABLE person ( pid int(11) NOT NULL DEFAULT 0, pname char(10) DEFAULT NULL, PRIMARY KEY (pid), CONSTRAINT person_ibfk_1 FOREIGN KEY (pid) REFERENCES office (oid)对应的类：与上同。映射：Person.hbm.xml office Office.hbm.xml无变化 测试：无变化一对一，通过连接表的单向关联这种方案比较少见,设置与通过外健实现的单向关联基本相同数据库表：CREATE TABLE person ( pid int(11) NOT NULL, pname char(10) DEFAULT NULL, PRIMARY KEY (pid)CREATE TABLE office ( oid int(11) NOT NULL, address varchar(20) DEFAULT NULL, PRIMARY KEY (oid)关联表CREATE TABLE person_office ( oid int(11) DEFAULT NULL, pid int(11) DEFAULT NULL, KEY FK1 (pid), KEY fk2 (oid), CONSTRAINT fk2 FOREIGN KEY (oid) REFERENCES office (oid), CONSTRAINT FK1 FOREIGN KEY (pid) REFERENCES person (pid)Person/Office类同上Mapping文件：Person.hbm.xml Office.hbm.xml 测试同上。第二类: 1对1双向关联一对一，通过连接表的双向关联数据库表同一对一，通过连接表的单向关联类：public class Person private Integer pid;/主键private String pname;private Office office;/对应的办公室public class Office private Integer oid;/Office id为主键private String address;private Person person;/对应的人映射：Person.hbm.xml Office.hbm.xml 一对一，通过主健实现的双向关联(应用稍多)数据库表格同通过主健实现的单向关联CREATE TABLE person ( pid int(11) NOT NULL DEFAULT 0, pname char(10) DEFAULT NULL, PRIMARY KEY (pid), CONSTRAINT person_ibfk_1 FOREIGN KEY (pid) REFERENCES office (oid)CREATE TABLE office ( oid int(11) NOT NULL DEFAULT 0, address varchar(20) DEFAULT NULL, PRIMARY KEY (oid)类同其他双向关联public class Person private Integer pid;/主键private String pname;private Office office;/对应的办公室public class Office private Integer oid;/Office id为主键private String address;private Person person;/对应的人 office public class Test public static void main(String args) Session session = HibernateSessionFactory.getSession();Transaction tx = session.beginTransaction();Person p = new Person();p.setPname