the nette framework implements nettedatabaseresultset only in one way

Your reasoning is correct. The ResultSet returned by most Nette\Database methods is a one way iterator so you cannot use it in multiple execution of a loop body. It is an optimization – once the loop advances the iterator, the previous row can be potentially garbage collected, which is useful to save memory on large database tables.

If you really need to iterate over a table multiple times, you can either:

• create $invoices multiple times
  • possibly moving the whole assignment into the loop inside the template
  • or creating function returning that result and calling it in the template
• or load the whole ResultSet into memory, for example by converting it into array. This is also what the documentation recommends:

  Over the ResultSet is possible to iterate only once, if we need to iterate multiple times, it is necessary to convert the result to the array via fetchAll() method.

But the best solution would be fixing it up to use JOINs, if possible. If you use FOREIGN KEYS in your database, you can avoid writing raw SQL and use the much nicer interface that will create JOINs for you transparently and efficiently, when you try to access data from other table through a column with a foreign key constraint.