Simple REST API not based on a particular predefined model
I think the key is to use the models differently. If you use onetomany or foreignkey references in your model construction you can more dynamically link different types of data together, then access that from the parent object. 
For example, for your user, you could create a basic user model and reference that in many other models such as interests, occupation, and have those models store very dynamic data. 
When you have the root user model object, you can access it's foreign key objects by either iterating through the dictionary of fields returned by the object or accessing the foreign key references directly with model.reference_set.all()
Well, I do my first steps with Django and Django REST framework. The problem I face is that all examples throughout the whole Internet are based on hard-coded models. But the whole concept of models frustrates me a little bit, because I'm used to deal with different data which comes from numerous sources (various relational databases and nosql - all that stuff). So, I do not want to stick to a particular model with a fixed number of predefined fields, but I want to specify them just at the moment when a user goes to a particular page of my app. 
Let's say I have a table or a collection in one of my databases, which stores information about users - it has any kinds of fields (not just email, name and likewise - all those fields as in all those examples throughout the web). So when a user goes to /users/ I connect to my datebase, get my table, set my cursor and populate my resultant dictionary with all rows and all fields I need. And REST API does all the rest. 
So, I need a "first-step" example wich starts from data, not from a model: you have a table "items" in your favorite database, when a user goes to /items/, he or she gets all data from that table. To make such simplistic api, you should do this and this... I need this kind of example.