Chapter 9: Data Access

The previous chapter showed you how the new Windows GUI Application Wizard can provide you with an easy route for accessing and querying any installed database. This chapter describes how you can manipulate this data.

Note: The programs and files that are output as a result of using the Windows GUI Applications Wizard are meant as a starting point for developing your own data access applications. They are not intended to be universally applicable to all situations, but are provided so that you can learn to use the basics. You can then adapt the code provided to suit your own, possibly more complex, needs.

The chapter Creating a Windows GUI Application in the Getting Started on-line book is a tutorial which includes practical details on how to use the wizard.

9.1 The Windows GUI Application Wizard

The Wizard process created a new screenset and automatically generated an associated COBOL program configured to the functionality you requested. Both the screenset and associated COBOL program were automatically added to your project.

If you want to access an installed database, you must have selected the OpenESQL Data Access option in Step 3: Select Screenset Features.

9.2 Accessing Installed Databases

There are two possible ways of viewing the results of your query after building your application, depending on the option you chose in Step 4 of the Windows GUI Applications Wizard:

List box view.

- or -
Grid view.

These views provide the same functionality but use different interfaces. The grid view has a more direct feel in use; the list view is more familiar to experienced Windows users.

When you run a query in grid view, all of the data is read into memory. This means that you can scroll the data up and down very quickly. In list box view, not all of the data is read into memory. In fact only one list box screen full is read in. It may therefore, be more practical to use a list box view when very large amounts of data are being used. For ways of improving performance with very large applications, see the topic Performance Programming in the Help.

The grid view of your database query might look like that in Figure 9-1.

Figure 9-1: Grid View of Database Query

The list box view of your database query might look like that in Figure 9-2.

Figure 9-2: List Box View of Database Query

The status bar is at the foot of the screen and gives information about the object that the mouse is over. When the mouse is over the general part of the screen, this text, which is actually a message box, tells you which type of function you have selected. Message boxes also give you information about immediate errors, for example, trying to edit a key field.

9.3 Manipulating the Data

You can perform the following functions:

Edit data in the database.
Insert a new row.
Delete a row.
Search for data by defining a new query.
Sort the data by column.

9.3.1 Edit Data

	Grid View	List View
Change data in a field	Select the field and specify the necessary changes, remembering that you cannot change key fields. If the edited field is in a column which has been sorted, your change may result in the whole row being moved to another part of the display.	Select the row to change and specify the necessary changes in the dialog box which opens. If the edited field is in a column which has been sorted, your change may result in the whole row being moved to another part of the display.
Move to the next column	Use either the mouse or the left and right arrow keys.
Delete data in a field	Select the field and press the Delete key.	Select the row to change and specify the necessary changes in the dialog box which opens. If the edited field is in a column which has been sorted, your change may result in the whole row being moved to another part of the display.
Refresh the screen	Click Run Query.	Click Run Query.

Note: Because concurrent versions of the same query can be open, Dialog System refreshes your query from disk before echoing any edits that you make to the data. This ensures that you see the most up-to-date version of the data.

9.3.2 Insert a New Row

	Grid View	List View
Insert a new row	Highlight the row below the insertion point. When you click New Row, you see an empty grid and you enter the new data in the top row.	Highlight the row below the insertion point. When you click New Row, you see a dialog box with entry fields for each column except for key fields. There is no validation for any of the entry fields.
Activate the insert	Press F7. Status Bar reports the result of your update.	Press Enter. The Status Bar reports the result of your update.
View the new line in your query	Click Run Query.

Note: Your new line may not be immediately visible. This could be a result of either of the following:

This data may be excluded by the current query. To see the new line you need to select a new query.
The new line is outside of the current view and you need to scroll to the new row's position.

9.3.3 Delete a Row

For both grid and list views, to delete a row of data, click the row number next to the data to be deleted and click Delete Row.

9.3.4 Search for Data

	Grid View	List View
Search for data	Click New Query. Highlight the field to search on. Enter your search criteria. Right-click in the field to see a pop-up menu. Select the logical operator (=, >, < and !=). The default is 'equal to'. Click Run Query to see the results of your search.	Click New Query. A dialog box is shown with entry fields for each field in your application. Enter your search criteria. Right-click in the field to see a pop-up menu. Select the logical operator (=, >, < and !=). The default is 'equal to'. Click Run Query to see the results of your search.

9.3.5 Sort Data

	Grid View	List View
Sort data in a column	Click on the column heading bar. You see: An up-arrow on the heading bar to indicate that the data is sorted in ascending order. A down arrow on the heading bar to indicate that the data is sorted in descending order.	Right-click in the list box. You see a pop-up menu from which you select the column to sort.