recursive entity reference in a view (tree view?)

Question

I have content type with entity reference to node of same content type. And I would like to show the nested references in the node view. Sort of a tree view.

How could I accomplish that?

I guess I need a view and a view field? But even not yet sure how to create a view which does recursive relationship...

It is for managing software dependencies and releases, there are libraries (=content type) dependent on 1:n libraries.

Answer 1

That can be accomplished with a custom module (great question by the way)...

First define a function to handle the whole process:

function make_tree() {

  // This is the nid of the root of our tree - could be passed in as an argument
  // instead of being static.
  $root_nid = 110;

  // First build an array with 3 fields - id, parent_id, title.
  $data = array();

  // We call add row once and then it's called resursivly to fetch each child.
  add_row($root_nid, null, $data);

  // Here we can inspect our data in it's flat form.
  //dpm($data);

  // Now turn the flat data into a multi-dimensional array.
  $tree = build_tree($data);

  // And inspect our tree.
  dpm($tree);

  // Could return the tree here or do anything we want with it...

}

Then define the function to build the flat array of data:

function add_row($nid, $parent_nid, &$data) {

  $node = node_load($nid);

  $data[$node->nid] = array(
    'id' => $node->nid,
    'parent_id' => $parent_nid,
    'title' => $node->title,
  );

  if(isset($node->field_dependent[LANGUAGE_NONE])) {
    // Now loop childeren to add rows for them too.
    // My entity relationship field is called dependent but rename here as
    // necesary.
    foreach($node->field_dependent[LANGUAGE_NONE] as $child) {
      add_row($child['target_id'], $node->nid, $data);
    }
  }

}

Once this step has been completed the $data array will look like this.

And then finally the function to turn the flat array into a multi-dimensional one (credit to this answer for this step):

function build_tree(array $elements, $parentId = 0) {
    $branch = array();
    foreach ($elements as $element) {
        if ($element['parent_id'] == $parentId) {
            $children = build_tree($elements, $element['id']);
            if ($children) {
                $element['children'] = $children;
            }
            $branch[] = $element;
        }
    }
    return $branch;
}

I've just tested this and my final array looks like this.