EntityNotFoundException: Bean has been deleted - lazy loading failed

问题

I'm making my first steps with the Play! Framework (v2.1-rc1) with Java and now I've faced my first problem with ebean. I have a navigation entity with a ManyToOne relationship to itself. As soon as I try to access the title field in a parentNavigation, I get the following error:

[EntityNotFoundException: Bean has been deleted - lazy loading failed]

As I found out, the error only appears if the parent navigation does not exist in the database. Shouldn't I receive an empty navigation object in this case?

Navigation Entity:

package models;

import javax.persistence.*;
import play.db.ebean.*;

@Entity
public class Navigation extends Model {

    @Id
    public Long id;

    @Column(name="c_title")
    public String title;

    @Column(name="id_parent")
    public Long parentId;

    @ManyToOne()
    @JoinColumn(name="id_parent")
    public Navigation parentNavigation;

    public static Finder<Long,Navigation> find = new Finder<Long,Navigation>(
        Long.class, Navigation.class
    );
}

My action in the controller:

public static Result index() {
    Navigation navigation = Navigation.find.byId(2L); // this one doesn't work, but the entry with ID 30 does
    return ok(views.html.app.index.render(navigation));
}

And my view:

@(navigation: Navigation)

@main("Welcome to Play 2.0") {

    This navigation: @navigation.title <br>
    Parent: @navigation.parentNavigation.title 

}

回答1:

If I understand correctly, you have a row with its parent_id column containing 2 (for example), but there is no row with ID 2 in the table.

If so, then it's normal to get an exception. Clean your data by setting all those inexistent parent_id to NULL, and add a foreign key constraint to the parent_id column so that this situation never happens anymore.

回答2:

In very general it's always better to check if relation isn't null before trying to access it:

This navigation: @navigation.title <br>
Parent: @if(navigation.parentNavigation != null){@navigation.parentNavigation.title} else {This nav has no parent}

Of course you can skip the else clause if it isn't required

来源：https://stackoverflow.com/questions/13779600/entitynotfoundexception-bean-has-been-deleted-lazy-loading-failed

标签

java

playframework

ebean

playframework-2.1