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

文章来源: EntityNotFoundException: Bean has been deleted - lazy loading failed