On our Slack community channel today one question was, how to get all other pages with the same tags like the current page. The solution - once you found it - seems to simple to be true.

We have a Page class with a many_many to our RelationTags like:

<?php

class Page extends SiteTree {

	private static $many_many = array(

	        'Relationtags' => 'Relationtag'

	    );

	public function getCMSFields() {

		  $fields = parent::getCMSFields();

			$field = TagField::create(

			    'Relationtags',

			    'Tags',

			    Relationtag::get(),

			    $this->Relationtags()

			)

			    ->setShouldLazyLoad(true) // tags should be lazy loaded

			    ->setCanCreate(true);     // new tag DataObjects can be created

			$fields->addFieldToTab('Root.Main', $field);

		  return $fields;

		 }


}

And of course the Tag Dataobject with the reverse $belongs_to:

<?php

class Relationtag extends DataObject {

    private static $db = array(

        'Title' => 'Varchar(200)',

    );


    private static $belongs_many_many = array(

        'Pages' => 'Page'

    );

}

Now how can we get all other Pages with the same tags? Our getter might look like this:

    public function getRelatedcontent(){

        return Page::get()->filter('Relationtags.ID', $this->Relationtags()->column('ID'))->exclude('ID', $this->ID);

    }

This way we get all other pages with at least one similar tag from our database.

This solution was tested in SilverStripe 3.5 and might work in previous versions.