jquery droppable -> avoid multiple drops of the same object
I have a container with different draggable <div>-elements and there is a list of some "target" divs, where the user can drop the draggable elements.

Example:
Imagine, you have a list of "tags" (House,Computer,Car,..) and a list of some documents  as target (all documents are part of the div `<div id="doclist">`). So the target is to assign the "tags" to the document using drag & drop. By the way, every tag-Div has an unique id (`<div id="e34a568b2">`)

Code for making the "tags" draggable:

    $('#taglist').find('div').draggable(
    	{helper: "clone"});
Code for making the documents "droppable":

    $('#doclist').droppable({
    		drop: function( event, ui )
                           {tag=ui.draggable;
                            tag.clone().appendTo( this );
                           } });


Until now, this works well.
The Problem is, that right now you can assign the same tag multiple times to same documents.
Example: document 1 can get tag "House" 5 times, Tag "Computer" 3 times. 


My target is, that every document can have every tag only one time.

I don't know, how to solve this problem. Right now, i thnik there are to ways:

1.) expand the "drop" function by walking trough the DOM $(this).find... to see, if there is an element with the same id - in this case, don't clone&append again. Probably this needs a lot of performance.

2.) use the "accept" feature of the draggable widget. But i don't know how to use this at this situation.

Thank you for any kind of help.
jquery droppable -> avoid multiple drops of the same object
===

I have a container with different draggable <div>-elements and there is a list of some "target" divs, where the user can drop the draggable elements.

Example:
Imagine, you have a list of "tags" (House,Computer,Car,..) and a list of some documents  as target (all documents are part of the div `<div id="doclist">`). So the target is to assign the "tags" to the document using drag & drop. By the way, every tag-Div has an unique id (`<div id="e34a568b2">`)

Code for making the "tags" draggable:

    $('#taglist').find('div').draggable(
    	{helper: "clone"});
Code for making the documents "droppable":

    $('#doclist').droppable({
    		drop: function( event, ui )
                           {tag=ui.draggable;
                            tag.clone().appendTo( this );
                           } });


Until now, this works well.
The Problem is, that right now you can assign the same tag multiple times to same documents.
Example: document 1 can get tag "House" 5 times, Tag "Computer" 3 times. 


My target is, that every document can have every tag only one time.

I don't know, how to solve this problem. Right now, i thnik there are to ways:

1.) expand the "drop" function by walking trough the DOM $(this).find... to see, if there is an element with the same id - in this case, don't clone&append again. Probably this needs a lot of performance.

2.) use the "accept" feature of the draggable widget. But i don't know how to use this at this situation.

Thank you for any kind of help.