public function project(array $columns)
{
$new_table = new RelationTable($columns);
if (array_diff($columns, $this->columns) == array()) {
$list = new FList($this->table);
$new_records = $list->foldl(function ($acc, $record) use($columns) {
$acc[] = $this->record_project($columns, $record);
return $acc;
}, array());
$new_table->insert_array($new_records);
}
return $new_table;
}
private function checkRelation(RelationTable $reltable, array $instances)
{
$pattern = $this->prepare_for_selection($instances);
$get = $reltable->select($pattern);
if ($get->isEmpty()) {
return FALSE;
} else {
return TRUE;
}
}