SQL Server

Subtract One MessageSet from Another

Demonstrates the Chilkat MessageSet.Subtract method, which removes from this set every identifier whose numeric value is also present in another MessageSet. The only argument is the other set. This example starts with ids 1:10, subtracts 2,4,6, and prints what remains.

Background: A common IMAP pattern is "process everything except what I've already handled." Subtract makes that a single call: remove the already-processed ids from a working set. The comparison is numeric only and this object's HasUids is preserved, so for meaningful results both sets should hold the same id type from the same mailbox. Passing the same object clears the set; passing an empty set changes nothing.

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-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    --  Demonstrates the MessageSet.Subtract method, which removes from this set every identifier
    --  that is also present in another MessageSet.  The only argument is the other MessageSet.

    DECLARE @msgSet int
    EXEC @hr = sp_OACreate 'Chilkat.MessageSet', @msgSet OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    --  Start with messages 1 through 10.
    EXEC sp_OAMethod @msgSet, 'FromCompactString', @success OUT, '1:10'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @msgSet, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @msgSet
        RETURN
      END

    --  The identifiers that have already been processed and should be excluded.
    DECLARE @processed int
    EXEC @hr = sp_OACreate 'Chilkat.MessageSet', @processed OUT

    EXEC sp_OAMethod @processed, 'FromCompactString', @success OUT, '2,4,6'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @processed, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @msgSet
        EXEC @hr = sp_OADestroy @processed
        RETURN
      END

    --  Remove the already-processed identifiers from msgSet.
    EXEC sp_OAMethod @msgSet, 'Subtract', NULL, @processed

    --  Show what remains.
    DECLARE @remaining nvarchar(4000)
    EXEC sp_OAMethod @msgSet, 'ToCompactString', @remaining OUT

    PRINT @remaining
    --  Output: 1,3,5,7:10

    EXEC @hr = sp_OADestroy @msgSet
    EXEC @hr = sp_OADestroy @processed


END
GO