[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=63202#comment-63202 ] 

Michael Pizzo commented on ODATA-827:
-------------------------------------

From discussion 2016-8-18:

1) Once defined, the alias MAY be used in the $filter, $orderby, and $expand expression.

~Customers?$expand=Orders($compute=price*qty as totalprice;$select=name,price,qty,totalprice)

2) In the ordered list of conceptually how query options are evaluated, $compute would be first.

3) $compute columns SHOULD be added to the default selection (in absence of $select) and can be explicitly $selected

4) Should $select=* include computed columns for non-entity (or collections of entity) types?  And, should $expand=* include computed entities/collections of entities?

5) Current expression restricts to simple results; we would want to include more than simple values for this usage.

6) $Compute doesn't affect the contextUrl. If included in $select, then the alias appears. Like any other dynamic property, it would have its type annotation in the payload.



> 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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