Returns a null value of a requested data type. Any valid data type with a null value. NULL returns a null result if the argument is null. Parameters are required to request a null value for some data types. The following table lists these data types and their parameters. Data type Parameter Example DT_ STRcharcountcodepage( DT_ STR,30,1252) casts 30 characters to the DT_ STR data type using the 1252 code page. DT_ WSTRcharcount( DT_ WSTR,20) casts 20 characters to the DT_ WSTR data type. DT_ BYTESbytecount( DT_ BYTES,50) casts 50 bytes to the DT_ BYTES data type. DT_ DECIMALscale( DT_ DECIMAL,2) casts a numeric value to the DT_ DECIMAL data type using a scale of 2. DT_ NUMERICprecisionscale( DT_ NUMERIC,10,3) casts a numeric value to the DT_ NUMERIC data type using a precision of 10 and a scale of 3. DT_ TEXTcodepage( DT_ TEXT,1252) casts a value to the DT_ TEXT data type using the 1252 code page. These examples return the null value of the data types: DT_ STR, DT_ DATE, and DT_ BOOL. NULL( DT_ STR,10,1252) NULL( DT_ DATE) NULL( DT_ BOOL) ISNULL ( SSIS Expression) Functions ( SSIS Expression).
Message 0 does not exist or has been deleted. Recent Topics Fog Creek Home.
A while ago, I wrote a bunch of extension methods for a Data Row to do just this sort of downcasting.because I hate writing repetitive drivel. Usage is simple: foreach( Data Row dr in some Data Table ) Date Time? dt = dr. Cast As Date Time Nullable( last Updated ) ; int id = dr. Cast As Int( transaction ID ) ; / etc. Here's the piece for Date Time values. Adding implementation for for other data types should be pretty trivial. Wouldn't be difficult to do the same sort of thing to a Data Reader if one was so inclined. I tried to come up with generic methods, but limitations in the way generics are done made it difficult or impossible to do and still get the behavior I wanted (e.g., null values rather than default( T) — getting default values for SQL NULLs that would make differentiating between 0 and null.difficult). public static class Data Row Extensions region downcast to Date Time public static Date Time Cast As Date Time( this Data Row row, int index ) return to Date Time( row[index] ) ; public static Date Time Cast As Date Time( this Data Row row, string column Name ) return to Date Time( row[column Name] ) ; public static Date Time? Cast As Date Time Nullable( this Data Row row, int index ) return to Date Time Nullable( row[index] public static Date Time? Cast As Date Time Nullable( this Data Row row, string column Name ) return to Date Time Nullable( row[column Name] ) ; region conversion helpers private static Date Time to Date Time( object o ) Date Time value = ( Date Time)o; return value; private static Date Time? to Date Time Nullable( object o ) bool has Value =!( o is DBNull Date Time? value = ( has Value? ( Date Time?) o : ( Date Time?) null ) ; return value; endregion endregion downcast to Date Time /. other implementations elided. for brevity.
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