[teiid-issues] [JBoss JIRA] Commented: (TEIID-1326) API request: rewrite query/command before it reaches the teiid planner

[Mark Addleman (JIRA)]

    [ https://jira.jboss.org/browse/TEIID-1326?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12559800#action_12559800 ] 

Mark Addleman commented on TEIID-1326:
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I've never gotten multi-source models to work using dynamic VDBs but assuming it does, I still see a problem.  Our data sources fall into two categories:  a set of app specific metadata tables and then data tables.  

The app specific metadata tables have a homogeneous structure although we currently allow the names of the tables to vary across data source.  These app specific metadata tables are then unioned together in a corresponding set of app specific metadata views from which the application reads its metadata.  We currently implement this as a recursive translator which dynamically rewrites queries (similar to the example above) and unions the appropriate tables.  If we used multi-source models, how would Teiid union together the data source specific metadata tables?  Would we require that all of the metadata tables have the same names?  

A further complication:  We use Teiid to access these app specific metadata tables which allow us to keep the physical storage of the metadata separate from the logical presentation.  Some of our metadata is physically stored in CSV files and we create Teiid views (again using this recursive translator) based on TEXTTABLE to create the appropriate logical Teiid view of the data.  If we went went the multi-source model approach, could the source be another view?  I see a problem trying to dynamically read the Teiid metadata.  Currently, to define a view using our recursive translator, you have to statically supply the Teiid metadata.

The data tables for our application have heterogeneous schemas and I think that static views on top of those to define security requirements (we probably can't use hasRole, instead we would write a custom security function) would work just fine.


> API request:  rewrite query/command before it reaches the teiid planner
> -----------------------------------------------------------------------
>
>                 Key: TEIID-1326
>                 URL: https://jira.jboss.org/browse/TEIID-1326
>             Project: Teiid
>          Issue Type: Feature Request
>          Components: Query Engine
>    Affects Versions: 7.1
>            Reporter: Mark Addleman
>            Assignee: Steven Hawkins
>
> I'd like an API to inspect and rewrite a user query/command before it reaches the Teiid planner. The use case is to rewrite the query/command to implement view-like capabilities.  For example:
> SELECT a,b,c FROM table1 AS t WHERE t.a='xyz'  would be rewritten as:
> SELECT a,b,c FROM (SELECT a,b,c FROM table2 UNION SELECT a,b,c FROM table3) AS t
> I imagine this API would be similar to the translator API:  it would receive a data structure representing the query/command and use a visitor to rewrite the query.  As a convenience, it would be nice to have something similar to the SQLConversionVisitor.

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