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Advanced usage

Batch requests

Example of batch request that contains 3 simple entity queries:

batch = northwind.create_batch()

batch.add_request(northwind.entity_sets.Employees.get_entity(108))
batch.add_request(northwind.entity_sets.Employees.get_entity(234))
batch.add_request(northwind.entity_sets.Employees.get_entity(23))

response = batch.execute()

print(response[0].EmployeeID, response[0].LastName)
print(response[1].EmployeeID, response[1].LastName)
print(response[2].EmployeeID, response[2].LastName)

Example of batch request that contains simple entity query as well as changest consisting of two requests for entity modification:

batch = northwind.create_batch()

batch.add_request(northwind.entity_sets.Employees.get_entity(108))

changeset = northwind.create_changeset()

changeset.add_request(northwind.entity_sets.Employees.update_entity(45).set(LastName='Douglas'))

batch.add_request(changeset)

response = batch.execute()

print(response[0].EmployeeID, response[0].LastName)

Error handling

PyOData returns HttpError when the response code does not match the expected code. Basically the exception is raised for all status codes >= 400 and its instances have the property response which holds return value of the library making HTTP requests.

For example, the following code show how to print out error details if Python Requests is used as the HTTP communication library.

try:
    new_data = create_request.execute()
except pyodata.exceptions.HttpError as ex:
    print(ex.response.text)

In the case you know the implementation of back-end part and you want to show accurate errors reported by your service, you can replace HttpError by your sub-class HttpError by assigning your type into the class member VendorType of the class HttpError.

from pyodata.exceptions import HttpError

class MyHttpError(HttpError):

    def __init__(self, message, response):
        super(MyHttpError, self).__init__('Better message', response)


HttpError.VendorType = MyHttpError

The class pyodata.vendor.SAP.BusinessGatewayError is an example of such an HTTP error handling.

Enable Logging

The library uses Python logging without own handler, so to enable logging it is enough to set log level to the desired value.

import logging

logging.basicConfig()
root_logger = logging.getLogger()
root_logger.setLevel(logging.DEBUG)

Observing HTTP traffic

There are cases where you need access to the transport protocol (http). For example: you need to read value of specific http header. Pyodata provides simple mechanism to observe all http requests and access low level properties from underlying network library (e.g. python requests).

You can use basic predefined observer class pyodata.utils.RequestObserverLastCall to catch last response headers:

from pyodata.utils import RequestObserverLastCall

last = RequestObserverLastCall()
northwind.entity_sets.Employees.get_entity(1).execute(last)
print(last.response.headers)

You can also write your own observer to cover more specific cases. This is an example of custom observer which stores status code of the last response.

from pyodata.utils import RequestObserver

class CatchStatusCode(RequestObserver):

    def __init__(self):
        self.status_code = None

    def http_response(self, response, request):
        self.status_code = response.status_code

last_status = RequestObserverLastCall()

northwind.entity_sets.Employees.get_entity(1).execute(last_status)
print(last_status.status_code)