4.3.4. OData Client¶

4.3.4.1. Overview¶

Warning: this client doesn’t support certificate validation when accessing servers through https URLs. This feature is coming soon...

4.3.4.2. Using the Client¶

The client implementation uses Python’s logging module to provide logging, when learning about the client it may help to turn logging up to “INFO” as it makes it clearer what the client is doing. “DEBUG” would show exactly what is passing over the wire.:

>>> import logging
>>> logging.basicConfig(level=logging.INFO)

To create a new client simply instantiate a Client object. You can pass the URL of the service root you wish to connect to directly to the constructor which will then call the service to download the list of feeds and the metadata document from which it will set the Client.model.

>>> from pyslet.odata2.client import Client
>>> c=Client("http://services.odata.org/V2/Northwind/Northwind.svc/")
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/ HTTP/1.1
INFO:root:Finished Response, status 200
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/$metadata HTTP/1.1
INFO:root:Finished Response, status 200
>>>

The Client.feeds attribute is a dictionary mapping the exposed feeds (by name) onto EntitySet instances. This makes it easy to open the feeds as EDM collections. In your code you’d typically use the with statement when opening the collection but for clarity we’ll continue on the python command line:

>>> products=c.feeds['Products'].OpenCollection()
>>> for p in products: print p
...
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products HTTP/1.1
INFO:root:Finished Response, status 200
1
2
3
... [and so on]
...
20
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products?$skiptoken=20 HTTP/1.1
INFO:root:Finished Response, status 200
21
22
23
... [and so on]
...
76
77
>>>

Note that products behaves like a dictionary, iterating through it iterates through the keys in the dictionary. In this case these are the keys of the entities in the collection of products. Notice that the client logs several requests to the server interspersed with the printed output. Subsequent requests use $skiptoken because the server is limiting the maximum page size. These calls are made as you iterate through the collection allowing you to iterate through very large collections.

The keys alone are of limited interest, let’s try a similar loop but this time we’ll print the product names as well:

>>> for k,p in products.iteritems(): print k,p['ProductName'].value
...
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products HTTP/1.1
INFO:root:Finished Response, status 200
1 Chai
2 Chang
3 Aniseed Syrup
...
...
20 Sir Rodney's Marmalade
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products?$skiptoken=20 HTTP/1.1
INFO:root:Finished Response, status 200
21 Sir Rodney's Scones
22 Gustaf's Knäckebröd
23 Tunnbröd
...
...
76 Lakkalikööri
77 Original Frankfurter grüne Soße
>>>

Sir Rodney’s Scones sound interesting, we can grab an individual record in the usual way:

>>> scones=products[21]
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products(21) HTTP/1.1
INFO:root:Finished Response, status 200
>>> for k,v in scones.data_items(): print k,v.value
...
ProductID 21
ProductName Sir Rodney's Scones
SupplierID 8
CategoryID 3
QuantityPerUnit 24 pkgs. x 4 pieces
UnitPrice 10.0000
UnitsInStock 3
UnitsOnOrder 40
ReorderLevel 5
Discontinued False
>>>

Well, I’ve simply got to have some of these, let’s use one of the navigation properties to load information about the supplier:

>>> supplier=scones['Supplier'].GetEntity()
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products(21)/Supplier HTTP/1.1
INFO:root:Finished Response, status 200
>>> for k,v in supplier.data_items(): print k,v.value
...
SupplierID 8
CompanyName Specialty Biscuits, Ltd.
ContactName Peter Wilson
ContactTitle Sales Representative
Address 29 King's Way
City Manchester
Region None
PostalCode M14 GSD
Country UK
Phone (161) 555-4448
Fax None
HomePage None

Attempting to load a non existent entity results in a KeyError of course:

>>> p=products[211]
INFO:root:Sending request to services.odata.org
INFO:root:GET /V2/Northwind/Northwind.svc/Products(211) HTTP/1.1
INFO:root:Finished Response, status 404
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Python/2.7/site-packages/pyslet/odata2/client.py", line 165, in __getitem__
        raise KeyError(key)
KeyError: 211

Finally, when we’re done, it is a good idea to close the open collection:

>>> products.close()

4.3.4.3. Reference¶

class pyslet.odata2.client.Client(serviceRoot=None, **kwargs)¶

Bases: pyslet.rfc5023.Client

An OData client.

Can be constructed with an optional URL specifying the service root of an OData service. The URL is passed directly to LoadService().

service = None¶: a pyslet.rfc5023.Service instance describing this service

feeds = None¶: a dictionary of feed titles, mapped to csdl.EntitySet instances

model = None¶: a metadata.Edmx instance containing the model for the service

LoadService(serviceRoot, metadata=None)¶

Configures this client to use the service at serviceRoot

serviceRoot

A string or pyslet.rfc2396.URI instance. The URI may now point to a local file though this must have an xml:base attribute to point to the true location of the service as calls to the feeds themselves require the use of http(s).

metadata (None)

A pyslet.rfc2396.URI instance pointing to the metadata file. This is usually derived automatically by adding $metadata to the service root but some services have inconsistent metadata models. You can download a copy, modify the model and use a local copy this way instead, e.g., by passing something like:

URI.from_path('metadata.xml')

If you use a local copy you must add an xml:base attribute to the root element indicating the true location of the $metadata file as the client uses this information to match feeds with the metadata model.

4.3.4.4. Exceptions¶

class pyslet.odata2.client.ClientException¶

Bases: exceptions.Exception

Base class for all client-specific exceptions.

class pyslet.odata2.client.AuthorizationRequired¶

Bases: pyslet.odata2.client.ClientException

The server returned a response code of 401 to the request.

class pyslet.odata2.client.UnexpectedHTTPResponse¶

Bases: pyslet.odata2.client.ClientException

The server returned an unexpected response code, typically a 500 internal server error. The error message contains details of the error response returned.