Entity creation-form: Prepopulate all existing entity-references of a field collection
You will need to create a custom module that alters the node creation form before it rendered using hook_form_FORM_ID_alter().

You want to edit the form_state which stores the information on how a form is filled out.

It should look something like this:

&lt;?php

/**
 * Module to prepopulate season price list with rooms
 */

/**
 * Implements hook_form_FORM_ID_alter(&amp;$form, &amp;$form_state)
 */

function mymodule_form_seasonal_prices_node_form_alter(&amp;$form, &amp;$form_state){

    // Load all of the room node ids into an array
    $node_type = "room";
    $result = db_query("SELECT nid FROM node WHERE type = '%s' ", $node_type);
    $nids = array();
  while ($obj = db_fetch_object($result)) {
    $nids[] = $obj-&gt;nid;
  }

  // Set the form state to include each room
  foreach($nids as $nid){
    $form_state-&gt;field_collection_you_want_to_edit[] = $nid
  }
}


You will need to do a bit of sleuthing to figure out what to put in the last line as it is specific to your build, and I don't know whether you need to set it to the $nid or node_load($nid) or something else.  But this should give you a framework to go on with.

If you haven't come across the Devel module yet, install it, and use dpm($form_State); to look at the structure of the variable so that you know what to change.

Finally, make sure you change the name of the function from 'mymodule' to whatever name you have given your module, make sure the machine names for your content types and form ids are correct (I just guessed them), and clear the cache so that Drupal picks up the hook.