OneToMany & ManyToOne mapping Spring Boot / Hibernate

Question

I have two tables with foreign key relations. I\'ve tried searching on how to do it and it always leads to OneToMany & ManyToOne mapping. I have these two tables.

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Answer 1

You have to annotate the Java fields not the getter like:

@OneToMany(targetEntity=User.class, mappedBy="userRole",cascade=CascadeType.ALL, fetch = FetchType.LAZY)
private List<User> user;

and for User.class

@ManyToOne
@JoinColumn(name="role_id")
private UserRole userRole;

In addition, do you have defined the role_id column in the user table? I can't see this in the screenshot

Answer 2

I can re-create your exception by mixing my annotation mapping between fields and properties. I see in the problem you described above you annotate the field Id, but then annotate the property userRole, if I do the same I get the same error. I can fix the error by either annotating just properties or fields. Both these models work:

@Entity
@Table(name = "USER")
public class User {


private Long id;
private UserRole userRole;
String userName;

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
public Long getId() {
    return id;
}


public void setId(Long id) {
    this.id = id;
}

@Column(name = "USER_NAME")
public String getUserName() {
    return userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}

@ManyToOne()
@JoinColumn(name="role_id")
public UserRole getUserRole() {
    return userRole;
}

public void setUserRole(UserRole userRole) {
    this.userRole = userRole;
}
}

This also works:

@Entity
@Table(name = "USER")
public class User {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;


@ManyToOne()
@JoinColumn(name="role_id")
private UserRole userRole;


@Column(name = "USER_NAME")
String userName;

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getUserName() {
    return userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}

public UserRole getUserRole() {
    return userRole;
}

public void setUserRole(UserRole userRole) {
    this.userRole = userRole;
}
}

Example of the other model object annotating the fields

@Entity
@Table(name = "USER")
public class User {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;


@ManyToOne()
@JoinColumn(name="role_id")
private UserRole userRole;


@Column(name = "USER_NAME")
String userName;

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getUserName() {
    return userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}

public UserRole getUserRole() {
    return userRole;
}

public void setUserRole(UserRole userRole) {
    this.userRole = userRole;
}
}

Test Code (I added this because there is often confusion that one must set the bidirectional relationship in order to get both users and userRole to persist with a save to the UserRole).

    List<User> users = new ArrayList<>();

    User user1 = new User();
    user1.setUserName("user1");
    users.add(user1);

    User user2 = new User();
    user2.setUserName("user2");
    users.add(user2);

    UserRole userRole = new UserRole();
    userRole.setRoleName("admin");
    //Unidirectional relationship
    user1.setUserRole(userRole);
    user2.setUserRole(userRole);
    //set Bidirectional relationship
    userRole.setUsers(users);

    userRole = userRoleRepository.save(userRole);

    //Show that the two users and the UserRole persisted
    UserRole result = userRoleRepository.findById(userRole.getId()).get();
    assertEquals(2, result.getUsers().size());

Answer 3

Can you move the relationship to a related object like this

@ManyToOne()
@JoinColumn(name="role_id", referencedColumnName = "role_id", insertable = false, updatable = false)    
private UserRole userRole;

and same do for userRole

@OneToMany(targetEntity=User.class, mappedBy="userRole",cascade=CascadeType.ALL, fetch = FetchType.LAZY)    
private List<User> user = new ArrayList<>();

Update

The jar file seems to be corrupted. Try removing the content from the .m2\repository and mvn clean install

OR

Right-click your project, select Maven, Update Project, check on Force Update of Snapshots/Releases.

Answer 4

Just a hint, check your entity classes and ensure you have included @Entity annotation just before the class declaration statement.

@Entity
public class MyEntityClass{
 //code
}

Then on any other entity class that uses MyEntityClass above under the @ManyToMany or @OneToMany relationship add the following.

@OneToMany(mappedBy="mappingItem", cascade=CascadeType.ALL, orphanRemoval=true)
@JsonIgnore
private List<MyEntityClass> myEntityClassItemList;

This approach worked for me some how, may be it might help.