Elements

Elements are WinCC OA data point elements with an archiving config (_archive) and an assigned archive group or alert config (alert_hdl_).

Elements have the following properties:

• id - Data point ID from WinCC OA.
• name - Full DPE name.
• dpTypeName - Name of the data point type of the DP of which the DPE belongs.
• unit - Unit of measurement defined in the _common config of the DPE.
• alias - Alias for DPE, defined in the _common config of the DPE.
• comment - The description of the DPE specified in the _common config of the DPE.
• variableType - Data type of the DPE according to the WinCC OA types.
• eventStorageGroupNames - Assigned event archive groups.
• alertGroupMap - Assigned alert archive group.

When you start the backend, you must synchronize the information about the archived data point elements. To do this, call the requestMetadataDeltaSynchronously function of the ConfigChannelHandler class. The first argument of the function is a list of archived DPEs (type MetadataRequest) for which the metadata is requested. An empty list requests the metadata for all DPEs that are archived in this backend. The result of this call is stored in the second argument of the function, which is of type MetadataDeltaResponse. It lists the metadata for the requested DPEs, which are divided into updates, deletions and new archived DPEs. The request should only be made in non-direct read mode.

// synchronizing metadata
  // skip metadata synchronization in case of directReadMode
  if (!directReadMode)
  {
      MetadataDeltaResponse metadataResponse;

      // send an empty request to get all metadata from the NGA Manager
      // also, you can send metadata from the database to get the only diff between metadata in the database and the NGA Manager
      MetadataRequest metadataRequest;
      configChannelHandler.requestMetadataDeltaSynchronously(metadataRequest, metadataResponse);
      logDebug("Backend received metadata changes: \n" + metadataResponse.DebugString());

      // proccess metadata from the NGA Manager
      MetadataHandler::processMetadata(metadataResponse);
}