SpringData 完全入门指南 (4)

Admin类：

@Entity @Table(name="t_admin") public class Admin { private int id; private String name; private Set<AdminRole> ars; public Admin() { ars = new HashSet<AdminRole>(); } public void add(AdminRole ar) { ars.add(ar); } @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; } @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" @LazyCollection(LazyCollectionOption.EXTRA)　　 public Set<AdminRole> getArs() { return ars; } public void setArs(Set<AdminRole> ars) { this.ars = ars; } }

Role类：

@Entity @Table(name="t_role") public class Role { private int id; private String name; private Set<AdminRole> ars; public Role() { ars = new HashSet<AdminRole>(); } public void add(AdminRole ar) { ars.add(ar); } @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; } @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" @LazyCollection(LazyCollectionOption.EXTRA) public Set<AdminRole> getArs() { return ars; } public void setArs(Set<AdminRole> ars) { this.ars = ars; } }

AdminRole类：

@Entity @Table(name="t_admin_role") public class AdminRole { private int id; private String name; private Admin admin; private Role role; @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; } @ManyToOne　　--->　　ManyToOne关联到Admin @JoinColumn(name="aid")　　 public Admin getAdmin() { return admin; } public void setAdmin(Admin admin) { this.admin = admin; } @ManyToOne　　--->　　 @JoinColumn(name="rid") public Role getRole() { return role; } public void setRole(Role role) { this.role = role; } }

小技巧: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

4.中间表

两个实体tb_user,tb_role
现在我们再tb_user或者tb_role中任意一个里面进行维护关系，多对对的情况下我们需要创建一个中间表来完成这个关系的映射，我们再tb_user中添加注解@ManyToMany然后再添加一个注解@JoinTable因为我们是要创建中间表所以要使用这个注解。JoinTable注解中我们添加如下例子中的内容，joinColumns当前表中的字段在中间表中的字段名称，inverseJoinColumns关联的外键表在中间表中的字段名称

@Entity @Table(name = "tb_user") @SequenceGenerator(name = "tb_user_sq",sequenceName = "tb_user_sqe") public class TbUser extends BaseEntity{ /** * 用户名 */ private String userName; /** * 登录名 */ private String loginName; /** * 登陆密码 */ private String passWord; /** * 手机号 */ private String telPhone; /** * 一个用户可以有多个角色 */ private List<TbRole> tbRoleList=new ArrayList<>(); public String getUserName() { return userName; } public void setUserName(String userName) { this.userName = userName; } public String getLoginName() { return loginName; } public void setLoginName(String loginName) { this.loginName = loginName; } public String getPassWord() { return passWord; } public void setPassWord(String passWord) { this.passWord = passWord; } public String getTelPhone() { return telPhone; } public void setTelPhone(String telPhone) { this.telPhone = telPhone; } @Id @Override @GeneratedValue(generator = "tb_user_sq",strategy = GenerationType.SEQUENCE) public Long getId() { return this.id; } @ManyToMany(cascade = CascadeType.REMOVE,fetch = FetchType.LAZY) @JoinTable(name = "tb_user_role",joinColumns = @JoinColumn(name="tb_user_id",referencedColumnName = "id"),inverseJoinColumns = @JoinColumn(name = "tb_role_id",referencedColumnName = "id")) public List<TbRole> getTbRoleList() { return tbRoleList; } public void setTbRoleList(List<TbRole> tbRoleList) { this.tbRoleList = tbRoleList; } }