Hello,

this really is a dumb question, but for some reason I cannot figure out how to get it to work.
My problem:

My domain provides several majordomo lists. Those have to be configured by mail. Now I want to write something to do it with a module: For each mailing list I want to build up a list of Members to keep track who is part of it. For adding members I want to have a dropdown list of Members to choose from. Sounds like a easy task for the DataObjectManager.

Unfortunatly I don't get it to work. Right now I have this:

class MailinglistePage extends Page {
static $db = array(
'Description'=>'Text',
'EMail'=>'Text'
);
static $has_one = array('Admin'=>'Member'
);

static $many_many = array('MailUser'=>'MailinglistenUser'
);

public function getCMSFields()
   {
      $f = parent::getCMSFields();
      $f->addFieldToTab("Root.Content.Mitglieder", new DataObjectManager(
         $this,
         'MailUser',
         'MailinglistenUser',
         array('User' => 'User'),
         'getCMSFields_forPopup'
      ));
      return $f;
   }

}

I have added a new class to wrap the Member:

class MailinglistenUser extends DataObject
{
   static $db = array (
   );
   
   static $has_one = array (
      'User' => 'Member'
   );
   
   static $belongs_many_many = array(
    'Mailingliste' => 'MailinglistePage'
   );
      
   public function getCMSFields_forPopup()
   {
    $members = DataObject::get("Member");
    $memberList = array();
    foreach($members as $member){
    $memberList[$member->ID] = $member->getName();
    }   
    return new FieldSet(
    new DropdownField('User', 'User', $memberList)
);
   }
}

With this, the cms looks good. Everything looks ready to add new Members to the Mailinglist. Unfortunatly it does not work. When I select a new member it is not inserted correctly and does not show up in the list. This is not surprising as the table MailinglistePage_MailUser stays empty. Only thing what happens is, that table MailinglistenUser each time gets a new entry with default UserID 0.
My question: Do I approach the problem in a sensible way?
If yes: What am I doing wrong?
If no: Any suggestions how to do it better?

Thank's for helping me.

I have followed your instructions. Additionally I have simplified my code to some extend:

class MailinglistenUser extends DataObject
{
   static $db = array (
    'Name'=>'Text',
    'Vorname'=>'Text',
    'Email'=>'Text'
   );
   
   static $has_one = array (
   
   );
   
   static $belongs_many_many = array(
    'Mailingliste' => 'MailinglistePage'
   );
      
   public function getCMSFields_forPopup()
   {
   
return new FieldSet(
new TextField('Name', 'Name'),
new TextField('Vorname', 'Vorname'),
new EmailField('Email', 'Email'));
   }
}

class MailinglistePage extends Page {
static $db = array(
'Description'=>'Text',
'EMail'=>'Text'
);
static $has_one = array('Admin'=>'Member'
);

static $many_many = array('MailUser'=>'MailinglistenUser'
);

public function getCMSFields()
   {
      $f = parent::getCMSFields();
      $f->addFieldToTab("Root.Content.Mitglieder", new ManyManyDataObjectManager(
         $this,
         'MailUser',
         'MailinglistenUser',
         array('Name' => 'Name',
         'Vorname'=>'Vorname',
         'Email'=>'Email'         
         ),
         'getCMSFields_forPopup'
      ));
      return $f;
   }
}

Now I can add MailinglistenUser and they show up in the cms. They are showing up in *all* MailinglistPages, though.
In the database the new User is created in the table MailinglistenUser, but the table MailinglistePage_MailUser is empty.

Oh, it already worked..
Thank's!