I have a wallpaper DataObject.
I'm managing my wallpaper in a DataObjectManager that is integrated in a category page.
A wallpaper has fields like title, image, rating and tags. The tags should be entered as String but stored in a seperate table....
So "blue, sky, nature" in a Textfield should be written into a table with a record for each tag like this
"blue"
"sky"
"nature"

First I had the tags as a simple string (sperated by ","). But as you start filtering wallpapers by tags and try to find other wallpapers with similar tags (like: show wallpapers that have the most amount of common tags) you want to use a second table and use sql's join queries.

So now I have a getCMSFields_forPopup() for my Picture Dataobject, that is being called, when adding/editing a picture to/of a gallery.
In this popup I have a nested DataObjectManager for the tags and it's not comfortable. Each time I add or edit a tag, the popup content is being replaced by the content of the add/edit dialog of the tags and when I'm finished adding/editing I can't get back to the original popup view. I can only press the general popup close and so the whole popup dissappears, although I didn't finish filling out the other fields (like choosing a title and other stuff) of the original popup view.

So either... is there a way to just close the inner DataObjectManager view instead of the whole popup or...
can I somehow have TextField for my tags where I can write something like "blue, sky, nature" but have a function that writes and reads those tags to/from other DataObjects that are bind by a has_many relationship ?

Here is a code excerpt:

<?php
class Wallpaper extends DataObject{
	static $db = array('Name'=>'Text');
	
	static $has_one = array('KategoriePage'=>'KategoriePage','WallpaperBild'=>'CustomImage');
	
	static $has_many = array('PictureTags'=>'PictureTag');

	public function getCMSFields_forPopup(){
			return new FieldSet(
				new ImageField('WallpaperBild','Das eigentliche Bild'),
				new TextField('Name','Name des Bildes'),
				new DataObjectManager($this,'PictureTags','PictureTag',PictureTag::$tabellen_namen,'getCMSFields_forPopup')
			);
	}
}
?>

<?php
class PictureTag extends DataObject{
	static $db = array('Name'=>'Text');

	static $has_one = array("Wallpaper"=>"Wallpaper");

	static $tabellen_namen = array('Name'=>'Tag');

	public function getCMSFields_forPopup(){
		return new FieldSet(
		new TextField('Name','Tag')
		);
	}
}
?>

I would just do it in your onAfterWrite()..

public function onAfterWrite() {
parent::onAfterWrite();
if($this->Tags) {
foreach(explode(" ", $this->Tags) as $tag) {
$o = new Tag(array('SomeField' => $tag));
$o->write();
}
}
}

I haven't tried this, cause I don't understand how those onBeforeWrite onAfterWrite work, and because writing is only one thing, reading the other. Or should I just make a fake default value of the Textfield that is being newly generated (from the tags objects) each time getCMSFields_forPopup is loaded ?
But I will try to give it a try (right now busy with big sql query :D)

Well, a Tag object would have a foreign key that associates it back to the holder dataobject. So you'd probably want to add

$o->YourHolderPageID = $this->ID;

to the function, as well.

how do I prevent the textfield (with the string) from beeing written to the database as well

I will try to simply not to mention it in the $db array, but I am stuck now with the filling of the Textfield

In the popup method of the Wallpaper DataObject

	public function getCMSFields_forPopup(){
		$tagsObj = DataObject::get("PictureTag","WallpaperID = ".$this->ID);
		foreach($tagsObj as $tag){
			if($tag->Name != ""){
				$tags .= $tag->Name;
			}
		}
		
		return new FieldSet(
		new TextField('Name','Name des Bildes'),
		new TextField("all_tags","Tags",$tags),

Maybe I'm approaching this completly wrong ?