JSON and objects


Morepath lets you define a JSON representations for arbitrary Python objects. When you return such an object from a json view, the object is automatically converted to JSON. When JSON comes in as the POST or PUT body of the request, this JSON can be automatically converted to a Python object. This system allows you to write views in terms of Python objects instead of JSON.


The morepath.App.dump_json() directive lets you define a function that turns a model of a particular class into JSON. Here we define it for an Item class:

class Item(object):
   def __init__(self, value):
       self.value = value

def dump_item_json(self, request):
    return { 'type': 'Item', 'x': self.value }

So for instance, Item('foo') is represented in JSON as:

  'type': 'Item',
  'x': 'foo'

If we omit the model argument from the directive, we define a general dump_json function that applies to all objects.

Now we can write a JSON view that just returns an Item instance:

def item_default(self, request):
    return self

The self we return in this view is an istance of Item. This is now automatically converted to a JSON object.


The App.load_json() directive lets you define a function that turns incoming JSON into a Python object. We detect JSON with the type field Item and interpret it as an Item instance, and pass through everything else:

def load_json(json, request):
    if json.get('type') != 'Item':
        return json
    return Item(json['x'])

When you write a json view you automatically get the Item instance as the body_obj attribute of the request:

@App.json(model=Collection, request_method='POST')
def collection_post(self, request):
    return "success!"