In a conventional client/server application, where database updates are initiated by a single application running on a client machine, PowerBuilder can manage DataWindow state information for you automatically. In a distributed application, the situation is somewhat different. Because application components are partitioned between the client and the server, you need to write logic to ensure that the data buffers and status flags for the DataWindow control on the client are synchronized with those for the DataStore on the server.
PowerBuilder provides four functions for synchronizing DataWindows and DataStores in a distributed application:
GetFullState
SetFullState
GetChanges
SetChanges
Although these functions are most useful in distributed applications, they can also be used in nondistributed applications where multiple DataWindows (or DataStores) must be synchronized.
To synchronize a DataWindow control on the client with a DataStore on the server, move the DataWindow data buffers and status flags back and forth between the client and the server whenever changes occur. The procedures for doing this are essentially the same whether the source of the changes resides on the client or the server.
To apply complete state information from one DataWindow (or DataStore) to another, you need to:
Invoke the GetFullState function to capture the current state of the source DataWindow.
Invoke the SetFullState function to apply the state of the source DataWindow to the target.
To apply changes from one DataWindow (or DataStore) to another, you need to:
Invoke the GetChanges function to capture changes from the source DataWindow.
Invoke the SetChanges function to apply changes from the source DataWindow to the target.
SetChanges can be applied to an empty DataWindow
You can call SetChanges to apply changes
to an empty DataWindow (or DataStore). The target DataWindow does
not need to contain a result set from a previous retrieval operation.
However, the DataWindow must have access to the DataWindow definition.
This means that you need to assign the DataWindow object to the
target DataWindow before calling SetChanges.
When you call GetFullState or GetChanges, PowerBuilder returns DataWindow state information in a Blob. The Blob returned from GetFullState provides everything required to recreate the DataWindow, including the data buffers, status flags, and complete DataWindow specification. The Blob returned from GetChanges provides data buffers and status flags for changed and deleted rows only.
By default, the Update function resets the update flags after a successful update. Therefore, when you call the Update function on the server, the status flags are automatically reset for the server DataStore. However, the update flags for the corresponding client DataWindow control are not reset. Therefore, if the Update function on the server DataStore succeeds, call ResetUpdate on the client DataWindow to reset the flags.
You can synchronize a single source DataWindow (or DataStore) with a single target DataWindow (or DataStore). Do not try to synchronize a single source with multiple targets, or vice versa.
