Selection::getReferencedTable always reloads when $row[$column] is NULL

[redwormik]

Using structure like in https://github.com/nette/database/blob/master/tests/Database/files/mysql-nette_test1.sql and doing this:

$table = $context->table('book');
foreach ($table as $row) {
    $translator = $row->ref('author', 'translator_id');
}

These queries are performed:

SELECT * FROM `book`
SELECT * FROM `author` WHERE (`id` IN (11, 12))
SELECT * FROM `author` WHERE (`id` IN (11, 12))

i.e. authors are needlessly refetched.

It does this both on master and 2.3.0 (PHP 5.5.9-1ubuntu4.6, MySQL 5.5.41-0ubuntu0.14.04.1).

It all goes down to https://github.com/nette/database/blob/master/src/Database/Table/Selection.php#L849 - the NULL key is never stored, so it is never found and performs a needless fetch.

The solution would be either to remember the NULL key on first fetch, or never fetch on NULL key. Which is better?

[redwormik]

Added attempt to fix this - Selection now doesn't REfetch when $row[$column] is NULL

[dg]

Thanks!