I have defined two classes: Products and Solutions.
The Product has many Solutions so I defined relationship many_many (static $has_many = array( "Solution" => "Solutions");).
Just to able add Solutions to Products in getCMSField, I defined TreeMultiselectFiel.
$MapSolutions = DataObject::get("SiteTree","`ClassName`='Solutions'")->toDropDownMap('ID','Title');
$fields->addFieldToTab("Root.Content.Main", new TreeMultiselectField('Solution','Description',$MapSolutions);,'Content');
During saving relationship are created - works fine. But when I refresh (F5 or CTRL+R) in TreeMultiselectField I can`t see which Solutions will be selected before write Content.
Thanks for help