[OASIS Issue Tracker] Commented: (ODATA-398) Define canonical function as a path segment that allows retrieving an entity by its id

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    [ http://tools.oasis-open.org/issues/browse/ODATA-398?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=33528#action_33528 ] 

Michael Pizzo commented on ODATA-398:
-------------------------------------

The cast segment allows the client to build a URL to access properties (i.e., for expanded navigations) in a strongly typed manner.

This is the same as:

GET ~Customers('ALFKI')/Northwind.PreferredCustomer?$filter=...$expand=...

In general, I view: 

GET ~$entity?$id=xxxx

to identify a single resource as functionally equivalent to a key-lookup for that resource. The metadataurl and payload should be identical.

> Define canonical function as a path segment that allows retrieving an entity by its id
> --------------------------------------------------------------------------------------
>
>                 Key: ODATA-398
>                 URL: http://tools.oasis-open.org/issues/browse/ODATA-398
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: Improvement
>          Components: OData ABNF Construction Rules, OData Protocol , OData URL Conventions 
>    Affects Versions: V4.0_CSD01
>         Environment: [Proposed]
>            Reporter: Michael Pizzo
>             Fix For: V4.0_CSD02
>
>
> Ids are the primary way to reference an instance in OData; they are used in relationships, in deltas, and can take the place of instances in payloads. We recommend, but do not require that ids be dereferenceable.
> Clients need a dependable way to get from an id to a reference, whether or not the reference is dereferencable. Although they could construct a query if they know the root set the id comes from, it would be useful and more discoverable to introduce a canonical query function, at the service root, for returning an instance given its id.
> Note that, since the id is likely to contain illegal characters, we have to pass the id as a query option, and will need to double single quotes in reference
> Options:
> GET ~myservice/getbyid(@id)?@id='.....'
> GET ~myservice/$getbyid?@id='.....'

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