[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:all-tabpanel ]

Michael Pizzo updated ODATA-827:
--------------------------------

    Proposal: 
Add "$compute" query option allowing additional computed properties to be added to each instance. The syntax is similar to the compute() transformation in Data Aggregation, i.e. $compute=<list of compute expressions>, but without the restriction to simple values: allowed compute expressions are any expressions valid in a $filter system query option on the input set.

More formally:
  compute          = '$compute' EQ computeItem *( COMMA computeItem )
  computeItem      = commonExpr RWS 'as' RWS computedProperty
  computedProperty = odataIdentifier         

$compute is also allowed as query option nested within $expand to add computed dynamic properties to expanded entities.

$compute is logically evaluated first, so the computed dynamic properties can be used in $expand, $filter, $orderby, and $select.

Computed structural properties SHOULD be added to the default selection (in absence of $select), and are treated as other dynamic properties:
- $select=* includes computed structural properties
- $expand=* includes computed navigation properties or computed entities/collections of entities
- appear in context URL same way as other (dynamic) properties

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

Note: in this example, totalprice is available outside of the expand as Orders/totalprice, as in:
GET ~Customers?$filter=Orders/totalprice gt 100&$expand=Orders($compute=price*qty as totalprice;$select=name,price,qty,totalprice)



  was:
Add "$compute" query option allowing additional computed properties to be added to each instance. The syntax is similar to the compute() transformation in Data Aggregation, i.e. $compute=<list of compute expressions>, but without the restriction to simple values: allowed compute expressions are any expressions valid in a $filter system query option on the input set.

More formally:
  compute          = '$compute' EQ computeItem *( COMMA computeItem )
  computeItem      = commonExpr RWS 'as' RWS computedProperty
  computedProperty = odataIdentifier         

$compute is also allowed as query option nested within $expand to add computed dynamic properties to expanded entities.

$compute is logically evaluated first, so the computed dynamic properties can be used in $expand, $filter, $orderby, and $select.

Computed structural properties SHOULD be added to the default selection (in absence of $select), and are treated as other dynamic properties:
- $select=* includes computed structural properties
- $expand=* includes computed navigation properties or computed entities/collections of entities
- appear in context URL same way as other (dynamic) properties

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


> 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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