title: Add field calculated from SQL query to Yii2 ActiveRecord model
body: <p>I'm writing code to return a list of locations that are within a specified region, and close to a certain latitude and longitude. The database layout is that there is a Location table that contains the businesses, a Region table that defines the regions (with UrlName being a slug that identifies the region), and a regionLocation table that maps regions to Locations. </p>
  
  <p>The SQL query is pretty hairy, but it calculates a virtual column named "Distance" that I would like to have accessible in the model returned.</p>
  
  <p>Here is a shortened version of the code that appears in my Location model:</p>
  
  <pre><code>        public static function getByRegionAndLatLong( $regionName, $lat, $long ) {
  
          $sql = "SELECT
              `Location`.`LocationId`,
              `Location`.`Latitude`,
              `Location`.`Longitude`,
                      (
                      3959 * acos (
                      cos ( radians( :Latitude ) )
                      * cos( radians( latitude ) )
                      * cos( radians( longitude ) - radians( :Longitude ) )
                      + sin ( radians( :Latitude ) )
                      * sin( radians( latitude ) )
                      )
                    ) AS Distance
                  FROM Location
                      LEFT JOIN RegionLocation RL
                      ON RL.LocationId = Location.LocationId
                      LEFT JOIN Region R
                      ON R.RegionId = RL.RegionId
                  WHERE R.UrlName= :UrlName
                  ORDER BY Distance ;
          ";
  
          return Location::findBySql( $sql, [
              ':Latitude' =&gt; $lat,
              ':Longitude' =&gt; $long,
              ':UrlName' =&gt; $UrlName
          ] )-&gt;all();
      }
  </code></pre>
  
  <p>The problem is that when I run the query, I would like for that calculated "Distance" column to be included in the results. But, since there is no actual field in the database named "Distance", Yii2's ActiveRecord class will not add the field to the generated models.</p>
  
  <p>I can get around it by creating a column in the Location table, named "Distance", but I'm hoping that there is a way to do this without making database changes.</p>
  
  <p>My ultimate intention was to have the model return an array of Location objects, with each Location object having a "Distance" attribute. Then, the controller would produce a json feed using code similar to the following:</p>
  
  <pre><code>    public function actionGetStudiosByLatLong( $regionName = '', $latitude='', $longitude='') {
          \Yii::$app-&gt;response-&gt;format = 'json';
  
          return Location::getByRegionAndLatLong( $regionName, $latitude, $longitude );
      }
  </code></pre>