SilverStripe - Adding 2 TreeDropdownFields, only one works - silverstripe

Question

I've run into a very bizarre issue while creating 2 TreeDropdownFields for a DataObject. For some reason, only 1 of the 2 TreeDropdownFields render correctly in the SilverStripe admin. The other doesn't render as a TreeDropdownField at all but just as a label:
Here is the code:
class HomeBanner extends DataObject {
public static $db = array(
'SortOrder' => 'Int',
'Title' => 'Varchar'
);
public static $has_one = array(
'Image' => 'Image',
'SecondaryImage' => 'Image',
'FirstLink' => 'SiteTree',
'SecondLink' => 'SiteTree'
);
public function getCMSFields() {
$fields = parent::getCMSFields();
$fields->removeFieldFromTab('Root.Main', 'PageID');
$fields->removeFieldFromTab('Root.Main', 'SortOrder');
$fields->addFieldToTab('Root.Main', new TreeDropdownField('FirstLinkID', 'First Link', 'SiteTree'));
$fields->addFieldToTab('Root.Main', new TreeDropdownField('SecondLinkID', 'Second Link', 'SiteTree'));
return $fields;
}
public static $summary_fields = array(
'ID' => 'ID',
'Title' => 'Title',
'Thumbnail' => 'Thumbnail'
);
public function getThumbnail() {
return $this->Image()->CMSThumbnail();
}
}
Here is what I have tried so far:
running dev/build/?flush=true
running ?flush=all and ?flush=1
logging out and logging back in after the dev/build + flushes
logging into the admin in another browser (I typically use Chrome but
logged into the site's admin on FireFox and saw the same problem)
The error logs report nothing -- they're clear
There are no errors in the console for Chrome's dev tools
Adding a third TreeDropdownField will allow the first 2 to render
properly but the third one will just show a label instead of a
TreeDropdownField
This format works, but doesn't save whatever is selected--it clears your choice as soon as you leave the page. Also, it deletes all that was saved already in the admin unless I remove it. I can't make changes or else the items saved get removed.):
$fields->addFieldToTab('Root.Main', new TreeDropdownField('SecondLink', 'Second Link', 'SiteTree', 'ID'));
Does anyone have any ideas as to why this could be happening? It doesn't seem to make sense that you can't have multiple TreeDropdownFields.

Answer 1

Reposting as this turned out to be the answer:
The name “HomeBanner” suggests to me that there should also be a has_one pointing back to HomePage or similar? The cause of this is probably that SilverStripe is automatically trying to set one of the has_one relations to point back to the page that the banner belongs to.
Similar conflicts can also happen when using code like this:
class Page extends SiteTree {
private static $has_many = [
'Banners' => 'Banner'
];
}
class Banner extends DataObject {
private static $has_one = [
'Page' => 'Page',
'LinkedPage' => 'Page'
];
}
As SilverStripe doesn't know whether it should use PageID or LinkedPageID to auto-populate that side of the has_many relation (GridField will try to automatically assign the correct has_one ID).
In these cases, you can use dot-notation to distinguish between them - you’d change it to $has_many = ['Banners' => 'Banner.Page'];. See https://docs.silverstripe.org/en/3/developer_guides/model/relations/#has-many for more info.