[OASIS Issue Tracker] (ODATA-827) introduce $compute query option

[OASIS Issues Tracker <workgroup_mailer@lists.oasis-open.org>]

    [ https://issues.oasis-open.org/browse/ODATA-827?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=61350#comment-61350 ] 

Mark Stafford commented on ODATA-827:
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If we're going for usability, I'd want us to think a bit more holistically about syntactic sugar in URLs. I suspect the most common use of this QSP would be to introduce new properties that get selected, which makes me ask why we wouldn't just support ~/lineItems?$select=*,(quantity*price) as total.

So question #1 in my mind is, would there be a way to support an "as"/"=" operator that is syntactic sugar for true projection? 

There may still be reasons to support $compute explicitly - e.g., that might be the best way to have a reusable calculated value - but that's all the more reason to look at what we're trying to achieve holistically.

Here's some interesting URLs to consider supporting:
* ~/lineItems?$select=*,(price*quantity) as total
* ~/lineItems?$select=*,total=(price*quantity)
* ~/orders?$expand=lineItems(select=*,(price*quantity) as total)
* ~/lineItems?$select=*,total&$orderby=total=(price*quantity) desc

> introduce $compute query option
> -------------------------------
>
>                 Key: ODATA-827
>                 URL: https://issues.oasis-open.org/browse/ODATA-827
>             Project: OASIS Open Data Protocol (OData) TC
>          Issue Type: Improvement
>          Components: OData Protocol, OData URL Conventions
>    Affects Versions: V4.0_WD01
>         Environment: New Query Capabilities
>            Reporter: Andrew Eisenberg
>              Labels: GoodIdea, Usability
>             Fix For: V4.01_WD01
>
>
> OData could be extended to allow derived computed values to be returned along with the properties of an entity.
> This could be expressed as:
> http://odata.netflix.com/v2/Catalog/Titles?$compute=substring(ShortSynopsis,20) as Summary&$select=Name,Summary
> In ODATA-9 we added support for an equivalent compute transformation in our Data Aggregation Extensions. 



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