Olingo4向后兼容吗？

Question

If I use Olingo4 libraries at client side (java), would they be compatible with ODATA 2.x services?

Thanks

Answer 1

It may work in some trivial scenarios, but even a simple count option differs much for different OData versions:

1. http://services.odata.org/V2/OData/OData.svc/Products/ ?$inlinecount=allpages&$format=json [v2]
2. http://services.odata.org/V4/OData/OData.svc/Products ?$count=true&$format=json [v4]

Official OData page suggests that Apache Olingo , odata4j and Jello Framework should have client implementations for OData 2. I've not worked with Olingo's client for v2, but I've heard it is very poor. And I couldn't find anything interesting from odata4j or Jello Framework (quick research).

In the worst scenario, you can go with a standard HTTP client. In the end, OData is based on REST.

Answer 2

The short answer is no .

The long answer is, Olingo or any other library is just an implementation of the OData Protocol. The version 4 of the protocol had breaking(read incompatible) changes, with the previous versions.

You can check out this link to get a list of all changes, including the incompatible ones in OData 4.

Now to be fully compatible, with both OData 2 and OData 4, you can read the OData-MaxVersion header sent by the client and based on it, you can send the response accordingly.This will require you to have both odata 2 and odata 4 implementations(using Olingo 2 and Olingo 4 or something else) running on your backend.

On a personal note, if you are starting out today and don't have a strong reason to have two implementations, it's not mandatory for an OData v4 service to support a lower version client.

An OData 4 service may respond to V1-V3 clients with 4XX-level errors.

http://docs.oasis-open.org/odata/odata/v4.0/errata02/os/complete/part1-protocol/odata-v4.0-errata02-os-part1-protocol-complete.html#_Toc406398370