将logisimayml模块与Play框架一起使用

Question

I am using the logisimayml 1.5 module with my Play app to produce yml from the contents in my live database. The module traverses the JPA classes to identify children to determine what gets written out into the yml.

So if I had two simple JPA classes like this:

public class Parent extends Model {

    @OneToMany(mappedBy = "parent", targetEntity = Child.class)
    public List<Child> children;

    ...
}

public class Child extends Model {

    @ManyToOne
    @JoinColumn(name = "parent_id")
    public Parent parent;

    ...
}

When I run logisimayml, it will produce a data.yml file that looks like this:

Parent(Parent_1):
 name: Bill
 children:
 - Child_1

Parent(Parent_2):
 name: Bill

Child(Child_3):
 name: Jill

Child(Child_1):
 name: Jill
 parent: Parent_1

Now the yml above does represent what the JPA classes represent however I would like to use the data.yml file for loading into my app using:

Fixtures.loadModels("data.yml");

This doesn't quite work because Bill is first and it wants to find the child Jill. Jill however has not yet been declared and therefore it falls over. This stems from the fact that I have used both @OneToMany in Parent and @ManyToOne in Child meaning it is bi-directional. I could remove the @OneToMany but I still want it in there for my code. Does anyone know what I could do to keep the JPA classes as they are but have the yml render without an infinite loop between the Parent and Child?

Here the exception I see when I start up my Play app pointing to the data.yml created by logisimayml:

RuntimeException occured : Cannot load fixture data.yml: No previous reference found for object of type sites with key User_25

The first object in the data.yml references User_25 as a child. The declaration of User_25 is much further down in my data.yml. As Luffy mentioned below, my simple Parent-Child example does not actually cause the exception to occur. My actual project has quite a large database so it is hard to replicate in a simple example here, though I thought it had something to do with the bi-directional annotations but I guess not after all. I also updated the data.yml for my example above. I actually do what Luffy did and created an actual project with the simple Parent-Child example and after running the module, it actually produced something slightly different than my hand crafted yml. Using that yml in the Fixtures.loadModels(..) call actually works though so it doesn't really reflect the issue exactly as I see it in production so I will have to get back to you on that.

Answer 1

Try to use "fetch = FetchType.LAZY" in ManyToOne annotation. This may help to fix your issue.

@ManyToOne(name = "parent_id", fetch = FetchType.LAZY)