title: qt merge models (reusing models)
body: <p>I have got several classes like Cat, Dog and Bird.
  My target is to have a QTableModel which merges all the properties from these classes for later use in a QTableView and a QDataMapper.</p>
  
  <p>In table A each datarow consists of one Cat, one Dog and one Bird.
  In table B each datarow consists of only two cats and no other animals. </p>
  
  <p>Is this the right approach:
   1. create a QTableModel for each class (CatModel: 1 column, DogModel: 2 columns, BirdModel: 3 columns)
   2. merge these models into one model which has 1+2+3=6 columns for table A (only 2 columns for table B)</p>
  
  <p>If this is the right idea, how can step 2 be implemented?
  I did read about the QIdentityProxyModel Class. But as far as i understand, this class is only meant to be used with one source model. My other idea was to create a new QTableModel with holds a list of all used models. Depending on the column of the ModelIndex the responsible model is calculated. E.g: index.column()==5 => it's the 2nd column of my bird. </p>