Supporting Folder Structure with Realm

Question

I am interested in representing folder system using RealmDB:

My first thought was:

 public class FolderItem extends RealmObject {
    public String name;
 }

 public class Folder extends FolderItem {
     public ArrayList<FolderItem> folderItems;
 }

 public  class File extends FolderItem {
    public String path;
 }

I am now seeing an error that Folder saying Annotated class Folder must extend a Realm class ... Does this mean recursive structures like this don't work or that inheritance is not fully supported? Or does anyone have better idea on how to do this?

I think realm does not support inheritance. This might help you https://github.com/realm/realm-java/issues/761 — Nongthonbam Tonthoi, May 07 '16 at 06:05
Inheritance is not supported. Only interfaces are. You could always use the same table and just have a string type to specify if it's a folder or a file. — EpicPandaForce, May 07 '16 at 06:14
Until Inheritence is supported you can use composition instead: http://stackoverflow.com/questions/49002/prefer-composition-over-inheritance — Christian Melchior, May 07 '16 at 06:16
Well now the problem is I am getting using composition is that ArrayList elements is not supported within FileItem as a type ... — FunctionallyReactive, May 07 '16 at 08:04
I have another question on doing this with composition so I can have levels? — FunctionallyReactive, May 07 '16 at 08:39

score 0 · Answer 1 · answered May 07 '16 at 23:07

If folders only contain files and other folders, you could easily represent it without needing inheritance:

 public class File {
    public String name;
 }

 public class Folder {
     public String name;
     public ArrayList<File>   files;
     public ArrayList<Folder> folders;
 }

Supporting Folder Structure with Realm

1 Answers1