api end point to retrieve list of connections

We should make this a constant then. Matching strings is a pain and lint won't catch typos in them. I'd suggest that a constant be created in the models. 

    TwitterConnection = 'TwitterConnection'

Then you can use that in place of the string in the:
     __mapper_args__ = {
        'polymorphic_identity': 'TwitterConnection'
    }

And here you can import that and use it to compare the type against.