12. Understanding .NET Data Provider Connectivity : .NET Data Provider Classes : IngresConnection Class : SendIngresDates Connection Keyword
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SendIngresDates Connection Keyword
The .NET Data Provider sends .NET DateTime parameter data to the Data Access Server (DAS) and the DBMS. The format of this DateTime parameter data sent by the provider depends on the level of support of the ANSI Date/Time data types.
In releases prior to Ingres 9.1 (also known as 2006 Release 2), the data is sent as a data type of INGRESDATE with a GMT timezone. Beginning with Ingres 9.1, the date/time data is sent with a data type of ANSI TIMESTAMP_WITH_TIMEZONE (TS_W_TZ) with a local datetime, local timezone, and microsecond data. This flexibility and adaptability to the capabilities of the DBMS is useful, but can have a side-effect when upgrading to new releases of Ingres.
When upgrading from a release of Ingres prior to 9.1, the behavior of the program can change under certain circumstances when datetime formerly sent as an INGRESDATE type is now sent as a TS_W_TZ type. Typically, no problem occurs because the TS_W_TZ data is converted as needed and any components of the data such as microseconds are discarded, depending on the target data type. In some cases, however, the change in data type can change the semantics of processing enough to become an issue.
For example, if datetime parameter data is sent to a query containing the the IFNULL( ? , ' ') function, the function may succeed or fail depending on the data type sent by the provider. If the provider sends the data as INGRESDATE type, then IFNULL(<ingresdate>, ' ' ) will execute correctly (returning the date or the empty string date if the parameter is null). Upon upgrade to Ingres 9.1 and later, the datetime parameter data is sent by the drivers as TIMESTAMP_WITH_TIMEZONE data type, and the IFNULL(<ts_w_tz>, ' ' ) will fail because the empty string date is not permitted in combination with ANSI TIMESTAMP_WITH_TIMEZONE.
The work-around for this problem is to wrap the INGRESDATE function around the parameter: IFNULL( INGRESDATE(?) , ' '). Changing every source reference in an application, however, may not be feasible.
Using the SendIngresDates=TRUE connection keyword tells the .NET Data Provider to send the date/time parameter data as INGRESDATE type and value (as if the server was pre-Ingres 9.1) to force the old behavior.
Caution! SendIngresDates=TRUE is intended to allow older applications to run with newer versions of Ingres. It should be used only in applications that access INGRESDATE columns only. Applications accessing ANSI Date/Time columns may experience other side effects of this feature due to loss of fractional second information and timezone format differences when the datetime parameter data is sent as INGRESDATE to an ANSI date/time column. Rather than using the SendIngresDates option, which is general in scope, we recommend using the IngresType.IngresDate parameter data type when sending .NET DateTime data that requires an INGRESDATE semantic context for the parameter.