title: Use `@Ignore` field in `@Query` result using Room
body: <p>I have two simple <code>location</code> and <code>houses</code> tables.
  I'd like to be able to fetch a <code>location</code> with all it's relevant information, and also add the <code>house</code> count to that query. The <code>houseCount</code> field is marked <code>@Ignored</code> since I don't want this saved. Room however can't seem to use the field for returning the data from a query like it would for any other class specified as a return object type for a query.</p>
  
  <p>My field:</p>
  
  <pre><code>@Ignore
  @ColumnInfo(name = EXTRA_COLUMN_LOCATION_HOUSE_COUNT)
  public int houseCount;
  </code></pre>
  
  <p>My location constructor:</p>
  
  <pre><code>public Location(long id, String name, LatLng location, long defaultRent, Date synced, int houseCount) {...}
  </code></pre>
  
  <p>My query:</p>
  
  <pre><code>SELECT locations.*, COUNT(DISTINCT houses.id) AS house_count FROM locations, houses WHERE locations.id = :id AND houses.location_id = :id
  </code></pre>
  
  <p>The warning:</p>
  
  <pre><code>Warning:(37, 14) The query returns some columns [house_count] which are not use by ug.karuhanga.logrealty.Models.Entities.Location. You can use @ColumnInfo annotation on the fields to specify the mapping.  You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: id, name, location, default_rent, synced, house_count. Fields in ug.karuhanga.logrealty.Models.Entities.Location: id, name, location, default_rent, synced.
  </code></pre>
  
  <p>and error:</p>
  
  <pre><code>Error:(33, 8) error: Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type).
  Tried the following constructors but they failed to match:
  Location(long,java.lang.String,ug.karuhanga.logrealty.Utils.LocationUtils.LatLng,long,java.util.Date,int) : [id : id, name : name, location : location, defaultRent : defaultRent, synced : synced, houseCount : null]
  </code></pre>