joining multiple entities in Spring JPA - mysql

Question

Have Users, Roles and User Roles tables.
Users
id
username
Roles
role_id
role_name
user_roles
user_id (fk users table)
role_id (fk roles table)
I defined my entities this way
user_roles Entity
#Column(name = "USER_ID")
private int userId;
#Column(name = "ROLE_ID")
private int roleId;
#ManyToOne()
#JoinColumn(name="ROLE_ID", insertable = false, updatable = false)
private RoleGroup userRole;
#ManyToOne()
#JoinColumn(name="id", insertable = false, updatable = false)
private User user;
User entity:
#Id
#Column(name="ID")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private int id;
#Column(name = "USER_NAME")
private String userName;
Roles Entity:
#Id
#Column(name="ROLE_ID")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Column(name = "ROLE_NAME")
private String roleName;
#OneToMany(targetEntity=UserRoleGroup.class, mappedBy="userRole",cascade=CascadeType.ALL,
fetch = FetchType.LAZY)
private List<UserRoleGroup> userGroup;
User table will store all lists of users. Roles table is the master table which is having 5 rows - (Admin, Read, manager..)
User Role Table will have user_id from user table and role_id from roles table.
Example
USER:
id user_name
1 test#gmail.com
2 abc#gmail.com
Roles
role_id Name
1 Admin
2 Manager
3 Read
User Roles
User_Id Role_ID
1 1
1 2
2 3
Repository
#Query("FROM UserRoleGroup AS urg LEFT JOIN urg.userRole AS ur LEFT JOIN urg.user AS u WHERE u.userName = ?1")
public List<UserRoleGroup> findAllUserRoles(String userName);
No compilation error, no runtime error, but query isn't returning anything whereas I have data in table. when i run query in MySql I am getting data

Answer 1

I was able to get this working with some minor changes to the entity classes and by adding a DTO. I think its not a good practice to pass around the entity to the client. Below is my implementation.
UserRoleGroup
#Entity
#Table#Data
public class UserRoleGroup {
#EmbeddedId
private UserRoleId id;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("userId")
private User user;
#ManyToOne(fetch = FetchType.LAZY)
#MapsId("roleId")
private Role role;
}
UserRoleId
#Embeddable
public static class UserRoleId implements Serializable {
private static final long serialVersionUID = 1L;
#Column(name = "user_id")
private Integer userId;
#Column(name = "role_id")
private Integer roleId;
public UserRoleId() {
}
public UserRoleId(Integer userId, Integer roleId) {
super();
this.userId = userId;
this.roleId = roleId;
}
public Integer getUserId() {
return userId;
}
public void setUserId(Integer userId) {
this.userId = userId;
}
public Integer getRoleId() {
return roleId;
}
public void setRoleId(Integer roleId) {
this.roleId = roleId;
}
#Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
UserRoleId that = (UserRoleId) o;
if (!userId.equals(that.userId)) return false;
return roleId.equals(that.roleId);
}
#Override
public int hashCode() {
int result = userId.hashCode();
result = 31 * result + roleId.hashCode();
return result;
}
}
User
import javax.persistence.*;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
/**
* user can have roles
* */
#Entity
#Table
public class User {
#Id
#Column(name="id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#Column(name = "username")
private String userName;
#OneToMany(mappedBy = "user",
cascade = CascadeType.ALL,
orphanRemoval = true)
private Set<UserRoleGroup> roles = new HashSet<>();
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
public Set<UserRoleGroup> getRoles() {
return roles;
}
public void setRoles(Set<UserRoleGroup> roles) {
this.roles = roles;
}
}
Role
import javax.persistence.*;
import java.util.ArrayList;
import java.util.List;
#Entity
#Table(name = "roles")
public class Role {
#Id
#Column(name="id")
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Integer id;
#Column(name = "role_name")
private String roleName;
#OneToMany(mappedBy="role",
cascade=CascadeType.ALL,
fetch = FetchType.LAZY)
private List<UserRoleGroup> users = new ArrayList<>();
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getRoleName() {
return roleName;
}
public void setRoleName(String roleName) {
this.roleName = roleName;
}
public List<UserRoleGroup> getUsers() {
return users;
}
public void setUsers(List<UserRoleGroup> users) {
this.users = users;
}
}
UserGroupRepository
import com.chait.json.generate.entity.UserRoleGroup;
import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;
import org.springframework.stereotype.Repository;
import java.util.List;
#Repository
public interface UserGroupRepository extends JpaRepository<UserRoleGroup,Integer> {
#Query(
"FROM UserRoleGroup AS urg LEFT JOIN urg.role AS ur LEFT JOIN urg.user AS u WHERE u.userName = ?1"
)
List<UserRoleGroup> findAllUserRoles(#Param("userName") String userName);
}
UserRoleDTO
#Data
#AllArgsConstructor
public class UserRoleDTO {
private String username;
private Set<String> roles;
}
UserRestController
#RestController
#RequestMapping("/users")
#RequiredArgsConstructor
public class UserRestController {
private final UserGroupRepository userGroupRepository;
#GetMapping("/{username}")
public ResponseEntity<UserRoleDTO> getUserRoleByUsername(
#PathVariable("username") String username
) {
List<UserRoleGroup> userRoleGroups = userGroupRepository.findAllUserRoles(username);
return ResponseEntity.ok(
new UserRoleDTO(
userRoleGroups.get(0).getUser().getUserName(),
userRoleGroups
.stream()
.map(UserRoleGroup::getRole)
.map(Role::getRoleName)
.collect(Collectors.toSet())
)
);
}
}