[Typo3] label_alt and select-box (MM)

[valli]

Hello all,
We are trying something like the following:

In a backend extension we have a database structure like this:


             categories
                 |
                 ^
sellers      products
    |            |
    ^            ^
sellers_products_mm


Our goal is to display in the backend a select box in the
interface of the table 'sellers' with not only strings from
the 'products' table but also concatenated strings from the
'categories' table.

We tried the following things:
- introduced the 'label_alt' and 'label_alt_force' in
   the $TCA['products']['ctrl'] array in the file ext_tables.php.
   => The label is now expanded and will also displayed in the
      mm-select-box of sellers.
   Problem: We found no way to include a string-field from 'categories'
            in the label_alt.
            => So it won't displayed in the mm-select-box

- do an ugly Hack: tried to select a join of categories and products
   in tca.php and overwrite $TCA["sellers"]["columns"]["products"].
   ("type" => "select"). Instead of 'foreign_table' fill the 'items'
   array.
   => Unfortunately doesn't work for MM.


Thanks for any ideas.

valli