This method computes aggregate values, qualities, and timestamps from data in the history database for the specified time domain for one or more items. The time domain is divided into subintervals of duration resampleInterval. The specified aggregate is calculated for each subinterval beginning with startTime by using the data within the next resampleInterval. This method is intended to provide values calculated with respect to the resample interval. For example, This method can provide hourly statistics such as Maximum, Minimum, Average, et. al. for each item during the specified time domain when resampleInterval is 1 hour.
The results are returned via the client's IOPCHDA_DataCallback::OnReadComplete method.
Syntax
| Visual Basic (Declaration) | |
|---|---|
Overloads Function ReadProcessed( _ ByVal transactionID As Integer, _ ByVal startTime As Date, _ ByVal endTime As Date, _ ByVal interval As TimeSpan, _ ByVal serverHandles() As Integer, _ ByVal aggregates() As Integer, _ ByRef cancelID As Integer, _ ByRef errors As Integer() _ ) As Integer | |
| C# | |
|---|---|
int ReadProcessed( int transactionID, DateTime startTime, DateTime endTime, TimeSpan interval, int[] serverHandles, int[] aggregates, 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.
- interval
- Interval between returned values.
- serverHandles
- The list item handles for the items to be read from the server.
- aggregates
- The list of aggregate values to be returned.
- 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
on 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