Friday, January 09, 2009

Enumerating Unique Constraints

There's no big deal about getting the list of UNIQUE constraints - they get listed as indexes by the CIndexesRowset class. When using this schema rowset you get everything that is implemented as an index by the database engine:
  • Indexes
  • Primary Key constraints
  • Unique constraints
While the schema rowset can distinguish between a regular index and a PRIMARY KEY, there's no telling if the listed index is a UNIQUE constraint or not. To correct this, you must first list all the UNIQUE constraints using the new CTableDefinition::FillUniqueArray method (see the updated sample below). As you can see, a unique index is also represented by a CIndex object, but stored in a different collection in the CTableSchema class. When the indexes are finally enumerated, the list is filtered for known UNIQUE constraints.

Another addition to the sample code is the ability to open any SQL Compact database on your device by using the Menu / Open sequence. The code that opens the database uses the installed SQL Compact OLE DB engines to "sense" the correct database format (see the updated CSchemaTreeFrame::OpenDataSource method).

On the next post I will start building the SQL Compact Explorer application by using this sample as a starting point. I will also use this application to bring back some of the code that I have been working on, namely the touch list and all the derivatives that have been developed but left unpublished.

Sample code: (155 KB)

No comments: