title: Query using eloquent whereMonth where date is string
body: <p>In one of the tables a column with type of <code>varchar</code> contains a date with the following format <code>day-month-year</code>. I would like to run a query using eloquent on that table with <code>whereYear</code> and <code>whereMonth</code>, but I get an error since the column <code>booking_date</code> is not of type Date. </p>
  
  <p>The query I am trying to run is</p>
  
  <pre><code>MyTable::whereYear('booking_date', '=', $year)
          -&gt;whereMonth('booking_date', '=', $month)
          -&gt;get();
  </code></pre>
  
  <p>And getting the following error</p>
  
  <pre><code>"SQLSTATE[42883]: Undefined function: 7 ERROR:  function pg_catalog.date_part(unknown, character varying) does not exist\nLINE 1: ...\" = $1 and \"said_table\".\"deleted_at\" is null) and extract(ye...\n                                                             ^\nHINT:  No function matches the given name and argument types. You might need to add explicit type casts.
  </code></pre>
  
  <p>Is there a way to cast the string value to a date before querying it, maybe with using raw expressions? If yes, any hints would be great. </p>