= FDO RFC 35 - Support Data Store level FDO capabilities  =

This page contains an change request (RFC) for the FDO Open Source project.  
More FDO RFCs can be found on the [wiki:FDORfcs RFCs] page.


== Status == 
 
||RFC Template Version||(1.0)|| 
||Submission Date|| June 08, 2009 ||
||Last Modified|| Dan Stoica[[Timestamp]]||
||Author||Dan Stoica, Orest Halustchak ||
||RFC Status||draft|| 
||Implementation Status||draft||
||Proposed Milestone||3.5.0.0||
||Assigned PSC guide(s)||Greg Boone||
||'''Voting History'''|| ||
||+1|| ||
||+0|| ||
||-0|| ||
||-1|| ||
 
== Overview ==

This RFC is for changing the behavior of existing FdoIConnection::GetXCapabilities() methods.

== Motivation ==

There are cases where a provider indicates support of a capability that is actually not supported by a data store the provider may connect to. Examples:

 * if an Oracle data store is not prepared for locking, this functionality is not supported in that data store although the provider itself is capable of providing the functionality. 
 * ODBC can connect to a variety of sources, each with varying levels of capability. 
 * there are cases where a user connected to a data store may not have the permission to write. This may be because the data store has a read-only flag (SHP, SDF) or a user has not been granted permissions to write to a data store (RDBMS). In this case, the information the provider level capability SupportsWrite returns is incorrect. 

== Proposed Solution ==

Change the behavior of GetXCapabilities(). On an open connection it will retrieve the exact capabilities, specific for that database. 
On a closed connection the current behavior will be preserved and provider level capabilities will be returned.

Note another solution has been considered. It consists in adding a flag on each GetXCapabilities() method, like:
{{{
FDO_API virtual FdoIConnectCapabilities *GetConnectionCapabilities(bool dataStoreLevel = false) = 0;
}}}

This alternative suggests that might be cases when a less accurate response is preferred over the accurate one. Therefore it is unlikely this flexibility is ever needed.


== Implications ==

Several cases have been identified so far as good candidates for improvements: 

SQLite, SDF, SHP: fix SupportsWrite() capability for the case of read-only files.[[BR]]
MySQL: depends on the storage driver; fix GetCommands() to indicate apply schema is only supported if FDO metadata.[[BR]]
ODBC: we officially support 6-7 data sources and we need to check all the capabilities.[[BR]]
Oracle: Oracle Express does not support long transactions. Fix GetCommands() so it doesn't return long transaction related commands.[[BR]]

== Test Plan ==

Existing providers units tests to be enhanced to exercise the changes.

== Funding/Resources ==

Autodesk to provide resources / funding.