Sharing information

The ShareData method allows you to share a result set among
two different DataStores or DataWindow controls. When you share
information, you remove the need to retrieve the same data multiple
times.

The ShareData method shares data retrieved by one DataWindow
control or DataStore (called the primary DataWindow) with another
DataWindow control or DataStore (the secondary DataWindow).

Result set descriptions must match

When you share data, the result set descriptions for the DataWindow
objects must be the same. However, the SELECT statements can be
different. For example, you could use the ShareData method to share
data between DataWindow objects that have the following SELECT statements
(because the result set descriptions are the same):

You can also share data between two DataWindow objects where
the source of one is a database and the source of the other is external.
As long as the lists of columns and their datatypes match, you can
share the data.

What is shared?

When you use the ShareData method, the following information
is shared:

• Primary buffer
• Delete buffer
• Filter buffer
• Sort order

ShareData does not share the formatting characteristics of
the DataWindow objects. That means you can use ShareData to apply
different presentations to the same result set.

When you alter the result set

If you perform an operation that affects the result set for
either the primary or the secondary DataWindow, the change affects
both of the objects sharing the data. Operations that alter the
buffers or the sort order of the secondary DataWindows are rerouted
to the primary DataWindow. For example, if you call the Update method
for the secondary DataWindow, the update operation is applied to
the primary DataWindow also.

Turning off sharing data

To turn off the sharing of data, you use the ShareDataOff
method. When you call ShareDataOff for a primary DataWindow, any
secondary DataWindows are disassociated and no longer contain data.
When you call ShareDataOff for a secondary DataWindow, that DataWindow
no longer contains data, but the primary DataWindow and other secondary
DataWindows are not affected.

In most cases you do not need to turn off sharing, because
the sharing of data is turned off automatically when a window is
closed and any DataWindow controls (or DataStores) associated with
the window are destroyed.

Crosstabs

You cannot share data with a DataWindow object that has the
Crosstab presentation style.

Example: printing data from a DataStore

Suppose you have a window called w_employees that
allows users to retrieve, update, and print employee data retrieved
from the database:

The DataWindow object displayed in the DataWindow control
is suitable for online display but not for printing. In this case,
you could define a second DataWindow object for printing that has
the same result set description as the object used for display and
assign the second object to a DataStore. You could then share data
between the DataStore and the DataWindow control. Whenever the user
asked to print the data in the window, you could print the contents
of the DataStore.

When the window or form opens

The code you write begins by establishing the hand pointer
as the current row indicator for the dw_employees DataWindow
control. Then the script sets the transaction object for dw_employees
and issues a Retrieve method to retrieve some data. After retrieving
data, the script creates a DataStore using the instance variable
or data member ids_datastore, and assigns the DataWindow object
d_employees to the DataStore. The final statement of the
script shares the result set for the dw_employees DataWindow
control with the DataStore.

This code is for the window’s Open event:

Code for the Update button

Code for the cb_update button applies the update
operation to the dw_employees DataWindow control.

This code is for the Update button’s Clicked event:

Code for the Print button

The Clicked event of the cb_print button prints the
contents of ids_datastore. Because the DataWindow object
for the DataStore is d_employees, the printed output uses
the presentation specified for this object.

This code is for the Print button’s Clicked event:

When the window or form closes

When the window closes, the DataStore gets destroyed.

This code is for the window’s Close event:

Example: using two DataStores to process data

Suppose you have a window called w_multi_view
that shows multiple views of the same result set. When the Employee
List radio button is selected, the window shows a list of employees
retrieved from the database:

When the Employee Salary Information radio button is selected,
the window displays a graph that shows employee salary information
by department:

This window has one DataWindow control called dw_display.
It uses two DataStores to process data retrieved from the database.
The first DataStore (ids_emp_list) shares its
result set with the second DataStore (ids_emp_graph). The
DataWindow objects associated with the two DataStores have the same result
set description.

When the window or form opens

When the window or form opens, the application sets the mouse
pointer to the hourglass shape. Then the code creates the two DataStores
and sets the DataWindow objects for the DataStores. Next the code
sets the transaction object for ids_emp_list and
issues a Retrieve method to retrieve some data.

After retrieving data, the code shares the result set for
ids_emp_list with ids_emp_graph.
The final statement triggers the Clicked event for the Employee
List radio button.

This code is for the window’s Open event:

Code for the Employee List radio button

The code for the Employee List radio button (called rb_emp_list)
sets the DataWindow object for the DataWindow control to be the
same as the DataWindow object for ids_emp_list.
Then the script displays the data by sharing the result set for
the ids_emp_list DataStore with the DataWindow control.

This code is for the Employee List radio button’s
Clicked event:

Code for the Employee Salary Information radio button

The code for the Employee Salary Information radio button
(called rb_graph) is similar to the code for the List radio
button. It sets the DataWindow object for the DataWindow control
to be the same as the DataWindow object for ids_emp_graph.
Then it displays the data by sharing the result set for the ids_emp_graph
DataStore with the DataWindow control.

This code is for the Employee Salary Information radio button’s
Clicked event:

When the window or form closes

When the window closes, the DataStores get destroyed.

This code is for the window’s Close event:

Use garbage collection Do not destroy the objects if they might still be in use by
another process—rely on garbage collection instead.

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