Add new Page using GridField - creates the child in root folder - silverstripe

Question

I would like to use GridField to view and create new child pages. Parent is DocumentHolder, child is Document. Both extend SiteTree. When I click to "Add Document" (button generated by grid), fill in the fields and confirm the form, the parent page is ignored and the page is created in root. It works well when I use DataObject. The code looks like this:
class DocumentHolder extends SiteTree
{
private static $allowed_children = array(
'Document'
);
private static $default_child = "Document";
public function getCMSFields()
{
$fields = parent::getCMSFields();
$gridField = new GridField('Documents', 'Documents', SiteTree::get('Document')->filter('ParentID', $this->ID), GridFieldConfig_RecordEditor::create());
$fields->addFieldToTab("Root.Uploads", $gridField);
return $fields;
}
}
class Document extends SiteTree
{
private static $db = array(
);
private static $has_one = array(
);
}
Thanks for help.

Answer 1

Since SiteTree already has a relationship to its Children pages set up, you may as well use it! Since allowed_children will only ever be documents, try this instead:
$gridField = new GridField('Documents', 'Documents', $this->Children(), GridFieldConfig_RecordEditor::create());

Answer 2

I ran into this problem earlier working on my holderpage module. You need to set the ParentID by default. Here's two strategies;
You can use populateDefaults on the child class. E.g.
class Document extends SiteTree
{
private static $default_parent = 'DocumentHolder';
private static $can_be_root = false;
public function populateDefaults(){
parent::populateDefaults();
$this->ParentID = DataObject::get_one(self::$default_parent)->ID;
}
...
Or you can manipulate the record in the gridfield with a custom GridFieldDetailForm implementation or via the updateItemEditForm callback.
<?php
class MyGridFieldDetailForm_ItemRequest extends GridFieldDetailForm_ItemRequest
{
public function ItemEditForm()
{
$form = parent::ItemEditForm();
if (! $this->record->exists() && $this->record->is_a('SiteTree')) {
$parent_page = $this->getController()->currentPage();
if ($parent_page && $parent_page->exists()) {
$this->record->ParentID = $parent_page->ID;
// update URLSegment #TODO perhaps more efficiently?
$field = $this->record->getCMSFields()->dataFieldByName('URLSegment');
$form->Fields()->replaceField('URLSegment', $field);
}
}
return $form;
}
}
This is more complicated although it allowed me to create an effortless module / addon ( https://github.com/briceburg/silverstripe-holderpage )