1.一对一的关系关联

需求：用户和角色一对一关联

package com.example.jpa.pojo;import javax.persistence.*;@Entity@Table(name = "t_user")public class User {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    /**     * CascadeType.PERSIST 只有User类新增时，     * 会级联Role对象新增。若Role对象在数据库存（跟新）在则抛异常（让Role变为持久态）     */    @OneToOne(cascade = CascadeType.PERSIST)    @JoinColumn(name = "role_id") //JoinColumn:维护一个外键的作用    private Role role;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Role getRole() {        return role;    }    public void setRole(Role role) {        this.role = role;    }}

package com.example.jpa.pojo;import javax.persistence.*;@Entity@Table(name = "t_role")public class Role {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    @OneToOne(mappedBy = "role")    private User user;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public User getUser() {        return user;    }    public void setUser(User user) {        this.user = user;    }}

/**     * 添加用户同时添加角色     */    @Test    public void test1()    {        //创建角色        Role role =new Role();        role.setName("小角色");        //创建用户        User user =new User();        user.setName("小用户");        //建立关系        user.setRole(role);        role.setUser(user);        //保存数据        userRepository.save(user);    }    /**     * 根据用户id查询用户，同时查询用户角色     */    @Test    public void test2()    {        User user =userRepository.getOne((long)13);        System.out.println(user);        Role role = user.getRole();        System.out.println(role);    }

2.一对多关联关系

需求：从角色到用户的一对多关联关系

package com.example.jpa.pojo;import javax.persistence.*;@Entity@Table(name = "t_user")public class User {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    @ManyToOne(cascade = CascadeType.PERSIST)    @JoinColumn(name = "role_id")    private Role role;    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Role getRole() {        return role;    }    public void setRole(Role role) {        this.role = role;    }}

package com.example.jpa.pojo;import javax.persistence.*;import java.util.HashSet;import java.util.Set;@Entity@Table(name = "t_role")public class Role {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    @OneToMany(mappedBy = "role")    private Set
     
       userSet = new HashSet<>();    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Set
      
        getUserSet() {        return userSet;    }    public void setUserSet(Set
       
         userSet) {        this.userSet = userSet;    }}
       
      
     

/**     * 添加用户同时添加角色     */    @Test    public void test1()    {        //创建角色        Role role =new Role();        role.setName("小角色");        //创建用户        User user =new User();        user.setName("小用户");        //建立关系        user.setRole(role);        role.getUserSet().add(user);        //保存数据        userRepository.save(user);    }    /**     * 根据用户id查询用户，同时查询用户角色     */    @Test    public void test2()    {        User user =userRepository.getOne((long)13);        System.out.println(user);        Role role = user.getRole();        System.out.println(role);    }

3.多对多的关联关系

需求：用户和角色多对多关系

package com.example.jpa.pojo;import javax.persistence.*;import java.util.HashSet;import java.util.Set;@Entity@Table(name = "t_user")public class User {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    @ManyToMany(cascade = CascadeType.PERSIST,fetch = FetchType.EAGER) //fetch = FetchType.EAGER:异步加载    //JoinTable 配置中间表信息    //joinColumns 建立当前表在中间表中的外键字段    @JoinTable(name = "t_user_role",joinColumns = @JoinColumn(name = "user_id")            ,inverseJoinColumns = @JoinColumn(name = "role_id"))   private Set
     
       roles =new HashSet<>();    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Set
      
        getRoles() {        return roles;    }    public void setRoles(Set
       
         roles) {        this.roles = roles;    }}
       
      
     

package com.example.jpa.pojo;import javax.persistence.*;import java.util.HashSet;import java.util.Set;@Entity@Table(name = "t_role")public class Role {    @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    @Column(name = "id")    private Long id;    @Column(name = "name")    private String name;    @ManyToMany(mappedBy = "roles")    private Set
     
       users =new HashSet<>();    public Long getId() {        return id;    }    public void setId(Long id) {        this.id = id;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }    public Set
      
        getUsers() {        return users;    }    public void setUsers(Set
       
         users) {        this.users = users;    }}
       
      
     

/**     * 添加用户同时添加角色     */    @Test    public void test1()    {        //创建角色        Role role =new Role();        role.setName("小角色");        //创建用户        User user1 =new User();        user1.setName("小用户1");        User user2 =new User();        user2.setName("小用户2");        //建立关系        role.getUsers().add(user1);        role.getUsers().add(user2);        user1.getRoles().add(role);        user2.getRoles().add(role);        //保存数据        userRepository.save(user1);        userRepository.save(user2);    }    /**     * 根据用户id查询用户，同时查询用户所有角色     */    @Test    public void test2()    {        User user =userRepository.getOne((long)13);        System.out.println(user);        Set
     
       roles = user.getRoles();        System.out.println(roles);    }