Question

Given the below JSON result from tastypie, I would like to create a new value at check.payments_total which is equal to the total amount of the payments (in this case, 44.00). Any clue on how to do this? I’m completely stumped. payments is a joined foreign key to the check table.

{
"objects": [
    {
        "check": {
            "id": "58a81b36-1ea6-403b-9902-a50cbd13cf2e",
            "number": 2,
            "payments": [
                {
                    "amount": "5.00",
                },
                {
                    "amount": "39.00",
                }
            ]
        }
    }
]
}

Answer 1

If for the response, then you could override the following method in your resource (the snippet is from tastypie.resources.Resource):

def alter_list_data_to_serialize(self, request, data):
    """
    A hook to alter list data just before it gets serialized & sent to the user.

    Useful for restructuring/renaming aspects of the what's going to be
    sent.

    Should accommodate for a list of objects, generally also including
    meta data.
    """
    return data

just include something like (not tested, consider to be pseudo-code):

 total_amount = 0.0
 for object in data[ 'objects' ]:
     total_amount += object[ 'amount' ]

 return { 'objects' : data[ 'objects' ], 'total_amount' : total_amount }

and you should be done.