In order to support API versioning, the default MetadataController is replaced with a VersionedMetadataController implementation. The main difference between the two is that the VersionedMetadataController will return service document and entity data model (EDM) information for each defined API version.

[ReportApiVersions]
public class VersionedMetadataController : MetadataController
{
  // omitted for brevity
}

Clients can now build proxies that have an affinity to a specific API version.

• ~/$metadata
• ~/$metadata?api-version=1.0
• ~/$metadata?api-version=2.0
• ~/$metadata?api-version=3.0

If a client does not specify an API version, the assumed value will be the configured default API version. When a client is ready to adopt a new version of the service, they can update their tooling to point to the appropriate API version of the metadata endpoint and generate a new proxy based on the version-specific EDMX.

The VersionedMetadataController also supports the HTTP OPTIONS method. This allows tools to query the service document (~/) or $metadata endpoints and provide a client with choices as to which API version they would like to create an OData client for.

For example, a tool can query the metadata endpoint:

OPTIONS /$metadata HTTP/1.1
host: tempuri.org

which will produce a response that looks like:

HTTP/1.1 200 OK
allow: GET, OPTIONS
api-supported-versions: 1.0, 2.0, 3.0
api-deprecated-versions: 0.9
odata-version: 4.0

A tool can choose to use this information is several ways. Any supported or deprecated API version is allowable. User interface tools should filter out deprecated API versions by default. Tools that do not afford user interaction will likely select the highest supported API version. Tools should also consider that the api-supported-versions and api-deprecated-versions HTTP headers can be reported multiple times as defined in RFC 2616 §4.2.

An OData service which does not support API versioning should return with HTTP 501 (Not Implemented) as defined in Section 9.3.1 of the OData v4.0 specification. However, given that API versioning behaviors of an OData service are not explicitly defined in the OData protocol, a client may also respond with HTTP 405 (Method Not Allowed). Tools should graceful fallback to the standard metadata query operations when API versioning information is unavailable.