OData version 2 and 3 differences

Question

OData protocol documentation (http://www.odata.org/documentation) describes two versions - 2 and 3.

What are the core differences between two versions?

Are both versions are supported by existing client libraries or version 2 is considered to be "legacy"?

To rephrase - are version 2 clients compatible with version 3?

Answer 1

You can find the list of all the differences between the two versions in the pdf of the Open Data Protocol (OData) Specification. Specifically, the changelog is at section "1.7 Versioning and Capability Negotiation"

Answer 2

In addition to a previous answer be aware that some client tools may still support only OData v2 protocol, so in case you need v3 specific features, you should make sure your client code is not limited by something like auto-generated proxy classes that are not capable of handling array types.

Here's an example when server exposes v3 features, but it's not possible to use them because Visual Studio WCF Data Service client proxy generator only supports v2:

http://bloggingabout.net/blogs/vagif/archive/2012/12/16/using-odata-protocol-v3-with-mongodata-odata-provider.aspx

Answer 3

There are lots of differences between the two versions. For example, OData v3 adds support for actions, functions, collection values, navigation properties on derived types, and stream properties. It also introduces a completely new serialization format for JSON ("application/json" means completely different things in the two versions).

When an OData client makes a request to a server, it can (and should) specify the maximum protocol version it can understand via the MaxDataServiceVersion HTTP header. A client written to only understand v2 of the protocol won't be able to understand a v3 payload.

I don't think I'd call v2 "legacy" or unsupported, but individual servers can choose whether or not to support requests that can only understand up to v2 (or v1). I think many existing clients out there support both v2 and v3. I know the WCF Data Services clients (desktop, windows phone, windows store, and silverlight) do support both.