Application Identity problem in Google App

I'd like to use @Embeddable annotation. So, it suggest to define as Application Identity. I created as the Data Nucleus Documentation. But it still error.

import java.util.List;
import javax.persistence.CascadeType;
import javax.persistence.Embeddable;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
@Embeddable
public class Category{
     @Id
     @GeneratedValue(strategy=GenerationType.IDENTITY)
     private String id;

     private String name;

     @OneToMany(mappedBy="category",cascade=CascadeType.ALL)
     private List<Product> products;

     public List<Product> getProducts() {
         return products;
     }

    public void setProdu开发者_高级运维cts(List<Product> products) {
        this.products = products;
     }

     public Category() {
     }

     public Category(String id,String name){
          this.id=id;
          this.name=name;
     }

     public String getId() {
         return id;
     }

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

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }
 }

Error is

Errors were encountered when initialising the specified MetaData. See the nested exceptions for details SEVERE: Class entity.Category has been specified with 1 primary key fields, but this class is using nondurable identity and should be application identity.

Remove @Id (and @Entity too for that matter) since the class is being embedded.