How can I prevent repeated items from being chosen when adding items to a child table? Do I have a way to access the list of items already selected before saving it? or put some validation so that the items already added are not available to select in the dependent dropdown? My specific case is a Sales Form in which the sold items are added to the daughter table Sale Items, but I do not want the same item to be added twice, since when selecting it you choose the quantity, if you want to add more quantity of the same item I want the user to edit the item, but not add a new repeated child record. I don't know if I explained myself correctly. I appreciate any help
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