how to prevent multiple entries on portal with same product?

[fileman922]

i have an invoice solution with a portal .  i need that the portal products can be type just one time , if somebody type the same product in another row , i will need that shows a message and then do something. 

i have been trying with validate menu and then unique value but it doesn't work. 

 

[Rick Whitelaw]

When you enter portal items you're creating new records in a related table as I'm sure you know. What you need is a field that is auto entered when the new record is created (other than the PK) that is validated as unique in the related table. This field could be a concatenated value of two fields entered. I don't know since I haven't access to your structure. An example would be a combination of date, product sku and client.

[comment]

a combination of date, product sku and client.

 

I think you mean a combination of the invoice ID and the product SKU.