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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)

Dynamically referenced EntitySet

If you need to work with many Entity Sets the same way or if you just need to pick up the used Entity Set name in run-time, you may find out the ability to get an instance of Entity Set proxy dynamically. Here is an example of how you can print a count of all employees:

count = getattr(northwind.entity_sets, 'Employees').get_entities().count().execute()
print(count)

Inspecting responses with a hook

Some OData services communicate domain errors via HTTP response headers on otherwise-200 responses. Because pyodata discards headers before returning the domain result, callers cannot detect these errors through the normal return value.

Client (and Service directly) accept an optional response_hook parameter — a Callable[[response], None] that fires before the domain handler runs, for every request type (including async_execute()). The hook receives the raw response object. Raising an exception from the hook propagates to the caller and prevents the domain handler from running.

import pyodata
import requests

SERVICE_URL = 'https://odata.example.com/MyService.svc'

def my_hook(response):
    if response.headers.get('x-custom-error'):
        raise RuntimeError(f"Service signalled error: {response.headers['x-custom-error']}")

service = pyodata.Client(SERVICE_URL, requests.Session(), response_hook=my_hook)

The hook must be stateless to be safe under concurrent and async use. If you need to handle SAP-specific header errors, use the ready-made hook in pyodata.vendor.SAP — see :doc:`vendors`.