This method reads the values, qualities, and timestamps from the history database for the specified time domain for one or more items. When bBounds is TRUE, the bounding values for the time domain are returned. This method is intended for use by clients wanting the actual data saved within the historian. The actual data may be compressed or may be all data collected for the item depending on the historian and the storage rules invoked when the item values were saved. The optional bounding values are provided to allow clients to interpolate values for the start and end times when trending the actual data on a display.
The results are returned via the client's IOPCHDA_DataCallback::OnReadComplete method.
Syntax
| Visual Basic (Declaration) | |
|---|---|
Overloads Function ReadRaw( _ ByVal transactionID As Integer, _ ByVal startTime As Date, _ ByVal endTime As Date, _ ByVal numValues As Integer, _ ByVal bounds As Boolean, _ ByVal serverHandles() As Integer, _ ByRef cancelID As Integer, _ ByRef errors As Integer() _ ) As Integer | |
| C# | |
|---|---|
int ReadRaw( int transactionID, DateTime startTime, DateTime endTime, int numValues, bool bounds, int[] serverHandles, out int cancelID, out int[] errors ) | |
Parameters
- transactionID
- An identifier created by the client and passed to the server in this call. The server shall return this identifier along with the results of this call.
- startTime
- The beginning of the history period to be read.
- endTime
- The end of the history period to be read.
- numValues
- The maximum number of values returned for any item over the time range. If only one time is specified, the time range must extend to return this number of values.
- bounds
- True if bounding values should be returned.
- serverHandles
- The list of server item handles for the items to be read.
- cancelID
- Place to return a Server generated ID to be used in case the operation needs to be canceled.
- errors
- Array of HRESULTs indicating whether the corresponding server handle was valid.
Return Value
HRESULTS success/error code.Remarks
The requests are queued and handled by a thread. The sample implementation has
one handling thread. To improve performance it may be necessary in some servers to have
multiple handling threads.
Requirements
Target Platforms: Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows 7, Windows Server 2008 family