在冬眠/休眠中获取n级深层关系

Question

I have implemented a Category domain which supports n level deep nesting.

The Category table contains a parent_id which is nothing but a id of Category table only.

public class Category {

String name;
//Reference to parent category
Category parentCategory;
//Child categories if this Category is a parent (Should I keep this in domain or remove it?)
Set categories;
}

A > B > C

M > N > O > P > Q

The above hierarchies can be created by setting id of A as parent_id of B, id of B as parent_id of C id of M as parent_id of N, id of N as parent id of O and so on..

Now I want to display a tree like structure of all the categories (using jsTree). What will be the best way to fetch the data?

Answer 1

You can use hasMany relationship to self for the child sub-categories.

public class Category {
   String name;
   //Reference to parent category
   Category parentCategory;
   static hasMany = [subCategories: Category]
}

Now you can either do a lazy fetch on the parent to get the child elements by using a '.' operation on the parent OR use a criteria to fetch all the child elements eagerly (provided this is inexpensive).

Note: We would only need the parentCategory in order to move up the tree from leaf node towards the root. If only one way traversal is needed then the hasMany mapping should be sufficient.