Editing from relatioships

[Antonio Sottocasa]

I have a problem in editing from 1 to many relationships.
Maybe something trivial regarding relationship definition or permissions that I am missing completely.

In the products - parts scenario, my tables and relationships would be:

Table 1: Products

relationship:
 [Parts]

parts.product = "$productname"

Table 2: Parts

relationship:

[Product]

products.productname = "$product"

Now, in the 'Products' relationship tab of the Parts table I can edit the product and save correctly.

However, in the 'Parts' relationship tab of the Product table, when I try to save I get an error informing me that the product field is mandatory, as if it were empty instead of being pre-compiled and uneditable.