Play Framework, OneToOne relationship not working

I used both your models as you posted in the above link and tested successfully. As @Andrei mentioned in his comment the problem is not in mapping, it should be the way you saving them. Following are the code snippets i used for testing.

User

@Entitypublic class User extends Model{    / ..... fields as it is in your post    public User(String user_id){        this.userId = user_id;    }    public static Finder<Long, User> find = new Finder<Long, User>(Long.class, User.class)    public static User findByUserID(String user_id){       /* Your models already in bi-directional relationship, so there is no need for external `fetch`, You can directly get `UserLegalName` object from `User`               model if there is any match found on `UserLegalName` for the input.  */       return find.where().eq("userId",user_id).findUnique();    }}

UserLegalName

@Entitypublic class UserLegalName extends Model {    / ..... fields as it is in your post    public UserLegalName(User user_id, String first_name, String last_name){        this.user = user_id;        this.firstName = first_name;        this.lastName = last_name;    }}

Controller

public class TestController extends Controller {    public static Result insertUser(String user_id, String fname, String lname)    {        User user = new User(user_id);        UserLegalName legal = new UserLegalName(user,fname,lname);        user.legalName = legal;        user.save();        return ok(user.legalName.firstName);    }    public static Result getUser(String user_id)    {        User user = User.findByUserID(user_id);        return ok(user.legalName.firstName);    }}

Routes

GET      /test/:userID/:fname/:lname       controllers.TestController.insertUser(userID : String, fname : String, lname : String)GET      /user/:userID       controllers.TestController.getUser(userID : String)

I suppose you set only one side of the relationship, and not both. As you have a bidirectional relationship you should set them both before persisting/merging, like:

userLegalName.setUser(user);user.setUserLegalName(userLegalName);entityManager.persist(userLegalName);entityManager.persist(user);