title: Raw select using jenssegers Laravel-MongoDB
body: <p>I add jenssegers Laravel-MongoDB package into my Laravel 4.2 project, and have a one problem. Maybe can help me. I cann't use DB::raw in select or get method. I need to change name of select column and add columns into one column, but Laravel return me an error.
  I try to do something like this:</p>
  
  <pre><code>$arr = StudentMark::join('students', 'students.id','=','student_marks.student_id')
          -&gt;select(array('student_marks.id',DB::raw('CONCAT(students.name, " ",
  students.surname, " (", students.index,") ") AS student')))-&gt;get();
  </code></pre>
  
  <p>But Laravel return me an error:</p>
  
  <pre><code>{"error":{"type":"ErrorException","message":"Illegal offset type","file":".....vendor\\jenssegers\\mongodb\\src\\Jenssegers\\Mongodb\\Query\\Builder.php","line":240}}
  </code></pre>
  
  <p>Can anybody help me?</p>