title: Django Rest Framework ModelSerializer get field data depending on query param
body: <p>I have a <code>ModelSerializer</code> with several field, many of them are <code>StringRelatedField</code> so the default representation of this fields is given by the <code>__str__</code> method on the model, in my case this are mostly <code>name</code> field in each model. In other cases I need to retrieve the <code>id</code> instead, so how can I do this, for example depending of a query param.</p>