[fdo-users] RE: Question on accessing Schema Mappings

Maksim Sestic max at geoinova.com
Tue Jul 24 09:09:08 EDT 2007

Hi Brent,

Thanks so much for the clarification. ISelect is the way to go, since I need
to stay as much provider-neutral as possible. Funny thing, every Autodesk's
example found on ADN promotes ISQLCommand for selecting datastore-resident
features. Is there some specific reason for that (i.e. speed)? I guess FDO
filtering also enables spatial queries, that's all I need beside data
properties and associations.

Maksim Sestic

Brent Robinson-5 wrote:
> Hi Maksim,
> Are you using the FDO API?
> If you are, the schema mappings can be retrieved by the following steps:
> 	 - create and execute a DescribeSchemaMapping command.
> FdoIDescribeSchemaMapping 
> 	returns an FdoPhysicalSchemaMappingCollection, which has an 
> 	FdoPhysicalSchemaMapping for each feature schema in your
> datastore. 	
> 	FdoPhysicalSchemaMapping, in itself, provides very little
> information, since the 
> 	schema mappings are different for each type or provider. 
> 	- cast each FdoPhysicalSchemaMapping to its provider-specific
> derivation. For 
> 	SqlServer it can be cast to FdoSqlServerOvPhysicalSchemaMapping.
> If you're
> 	Working from the FDO source code, the header for this class is
> in 
> Providers\GenericRdbms\Inc\Rdbms\Override\SqlServer\SqlServerOvPhysicalS
> chemaMapping.h
> 	and the required DLL's are SqlServerOverrides.dll and
> RdbmsOverrides.dll
> 	- From FdoSqlServerOvPhysicalSchemaMapping, you can get the list
> of classes 
> 	For this schema and, from each class, its list of properties.
> Each property has
> 	a column object that indicates the corresponding column name. 
> The handling of default mappings ( column name same as property name )
> depends on the IncludeDefaults setting on the FdoIDescribeSchemaMapping.
> If true, all properties and their column mappings are listed. If false,
> only properties, where property and column name different are present.
> An alternative to the above is to run the query using the FdoISelect
> command. This command takes property names and automatically handles the
> translation to column names when it runs the query against the RDBMS.
> However, FdoISelect does not provide full SQL functionality, so there
> are cases where you'll need to use ISQLDataReader.
> Brent.
> -----Original Message-----
> From: fdo-users-bounces at lists.osgeo.org
> [mailto:fdo-users-bounces at lists.osgeo.org] On Behalf Of Maksim Sestic
> Sent: Monday, July 23, 2007 6:06 AM
> To: fdo-users at lists.osgeo.org
> Subject: [fdo-users] Question on accessing Schema Mappings
> Dear all,
> I established Microsoft SQL Server hosted DataStore with several
> FeatureSchemas, containing several FeatureClasses, containing several
> Properties. Actual data was instantiated on all beforementioned
> elements,
> everything works OK.
> During model creation provider imposes implicit SchemaMappings on
> several
> PropertyDefinitions, which is OK during data insertion. Querying data
> introduces problems since ISQLDataReader takes actual column name as a
> parameter to get access to stored property value. In certain cases
> column
> names carry mapped names (e.g. DataPropertyDefintion named "Number" gets
> mapped to a column named "number1"). I've noticed that every schema
> mapping
> gets persisted within dbo.f_attributedefinition table.
> Now for the question - how do I gain access to (auto)generated mappings
> on
> model elements - Schema, Class and Property? What's the procedure to get
> i.e. PropertyDefinition for given ISQLDataReader column name (or
> vice-versa)?
> Regards,
> Maksim Sestic
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