[TYPO3-mvc] Query fields of external table

[Michael Ruhdorfer]

hi,

I am trying to do a search where (a user has products) the username 
should be found. I am trying to access the user in the products repository:

$constraints[] = $query->like('user.username', '%'.$keyword.'%');

but it seems as if the wrong table is searched through, for I am using 
the fe_users table, the error message I get is as following:

#1247602160: You have an error in your SQL syntax; check the manual that 
corresponds to your MySQL server version for the right syntax to use 
near 'ON tx_myext_domain_model_products.user=.uid WHERE (((((( ... OR 
username LIKE '%keyword%')

When I change 'user.username' to 'user' and I am searching the ids, the 
result is returned the right way. What am I doing wrong, or isn't that 
possible (yet)?

thx, michael