Improve schema nesting

[rbw]

Adds support for any level of nesting and fixes bugs related to fetching of nested objects and how they are merged with the main document.

Model declaration

class ProductCatalogItem(ModelSchema):
    sys_id = aiosnow.fields.String()
    no_order_now = aiosnow.fields.Boolean()
    delivery_time = aiosnow.fields.DateTime()
    sys_name = aiosnow.fields.String()

class HardwareModel(ModelSchema):
    sys_id = aiosnow.fields.String()
    name = aiosnow.fields.String()
    manufacturer = aiosnow.fields.StringMap()
    model_number = aiosnow.fields.String()
    barcode = aiosnow.fields.String()
    power_consumption = aiosnow.fields.Integer()
    rack_units = aiosnow.fields.Integer()
    product_catalog_item = ProductCatalogItem

class Hardware(aiosnow.TableModel):
    sys_id = aiosnow.fields.String(is_primary=True)
    asset_tag = aiosnow.fields.String()
    install_status = aiosnow.fields.StringMap()
    location = aiosnow.fields.String(pluck=Pluck.DISPLAY_VALUE)
    company = aiosnow.fields.StringMap()
    ci = aiosnow.fields.String(pluck=Pluck.DISPLAY_VALUE)
    serial_number = aiosnow.fields.String()
    model = HardwareModel
    sys_class_name = aiosnow.fields.String(pluck=Pluck.DISPLAY_VALUE)
    product_catalog_item = ProductCatalogItem

Response data

[ { 'asset_tag': 'P1000479',
    'ci': 'MacBook Pro 15"',
    'company': <StringMapping [key=81fdf9ebac1d55eb4cb89f136a082555, value=ACME China]>,
    'install_status': <StringMapping [key=1, value=In use]>,
    'location': '2500 West Daming Road, Shanghai',
    'model': { 'barcode': 'MD318LL/A',
               'manufacturer': <StringMapping [key=b7e9e843c0a80169009a5a485bb2a2b5, value=Apple]>,
               'model_number': 'MD318LL/A',
               'name': 'MacBook Pro 15"',
               'power_consumption': None,
               'product_catalog_item': { 'delivery_time': datetime.datetime(1970, 1, 3, 0, 0),
                                         'no_order_now': False,
                                         'sys_id': '2ab7077237153000158bbfc8bcbe5da9',
                                         'sys_name': 'Apple MacBook Pro 15"'},
               'rack_units': 1,
               'sys_id': 'd501454f1b1310002502fbcd2c071334'},
    'product_catalog_item': { 'delivery_time': datetime.datetime(1970, 1, 3, 0, 0),
                              'no_order_now': False,
                              'sys_id': '2ab7077237153000158bbfc8bcbe5da9',
                              'sys_name': 'Apple MacBook Pro 15"'},
    'serial_number': 'BQP-854-D33246-GH',
    'sys_class_name': 'Hardware',
    'sys_id': 'd501454f1b1310002502fbcd2c071334'}]