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  • UdaWikiWeb.OLEDBExposingMetadata(Last) -- Owiki? , 2016-08-19 15:00:37 Edit owiki 2016-08-19 15:00:37

    Exposing Metadata

    The OpenLink Provider expose information about the columns of a rowset through IColumnsInfo. The information for each column is returned in a DBCOLUMNINFO structure. OLE DB also has an optional metadata interface, IColumnsRowset; the OpenLink provider does not implement this interface.

    The GetColumnInfo method returns metadata that is most commonly used by consumers: column ID, column name, the ordinal number of the column in the rowset, the column's data type, and so on.

    The provider returns the information in an array of DBCOLUMNINFO structures, one DBCOLUMNINFO structure per column in the rowset. The order of the structures returned in the array is the order in which the columns appear in the rowset.


    Columns that have an ODBC SQL type of SQL_LONGVARCHAR or SQL_LONGVARBINARY are returned as type DBTYPE_BYTES or DBTYPE_STR, and the DBCOLUMNFLAG_ISLONG is set in the dwFlags element of the DBCOLUMNINFO structure.

    Returning Column Ordinals

    Columns in a rowset are identified by a column ID, which is a value of type DBID in the DBCOLUMNINFO structure.

    The MapColumnIDs method returns column ordinals for all column IDs provided in the rgColumnIDs array. Column ordinals do not change during the life of the rowset, but may change between different instances of the rowset.

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