Foreign key on reference entity in ng-admin

I'm trying to build an admin interface using ng-admin. I'm using a reference field to link one main entity (Post, for example) to a different entity (Comment) that has a many-to-one relationship (one Post has many Comments).

On a listView() of Posts I must display the last Comment of each Post, but as I can see from the relationships documentation of ng-admin I can't because in my API the foreign key is not on the main entity but on the secondary one.

In other words, I have post_id in the Comment entity but I am doing a listView() of Posts so I can't access any Comment.

Is there a workaround for this issue? Can I reference to an external entity from an entity that does not contain the reference key itself?

I'll add a simple JSON to make the example more clear.

// Post
{ 
  id: 1,
  title: 'post n1',
  body: 'bla bla bla very cool'
}

// Comment
{ 
  id: 1,
  body: 'yo bro'
  post_id: 1
}

Thank you

Solution

From personal experience and looking at the reference it looks like the only to get results similar to what you're looking for are by using a referenced_list (see http://ng-admin-book.marmelab.com/doc/reference/Field.html#-referenced-list-field-type). The first sentence matches your case exactly:

"The referenced_list type maps a one-to-many relationship where the foreign key is located in another entity."

Using it would then be something like this:

nga.field('comments', 'referenced_list')
    .targetEntity(comments)
    .targetReferenceField('post_id')

This should get you a list of the comments connected to that post. HOWEVER, since this returns a list, you cannot use it with listView (you can't nest a list in a list).

Unfortunately I don't think there's any way to use reference to get a similar result, because reference uses one of the keys of the object to search.