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Day 7
Using the Visdata
Program
Today you will learn everything you need to know about using one of the most valuable
sample programs that is shipped with Visual Basic 5--the Visdata sample application.
You'll learn how to use the Visdata sample application to maintain your database
files, including creating and modifying database tables, performing simple data entry
on existing tables, and using Visdata to make backup copies of existing databases.
NOTE: This lesson does not cover the source code
for Visdata or talk about how Visdata works. You can, however, learn a great deal
by bringing the Visdata project up within Visual Basic 5 and studying the modules
and forms. Studying Visdata in this manner is an excellent way to learn how to create
dynamic data entry forms, handle SQL processing, and link your Visual Basic 5 programs
to back-end database servers using ODBC drivers.
Using Visdata to
Maintain Databases and Tables
Visdata is an excellent tool for constructing and managing databases for your
Visual Basic 5 applications. You can use it to create new databases, add or modify
tables and indexes, establish relationships, set user and group access rights, test
and store SQL query statements, and perform data entry on existing tables.
Visdata can present dynamic data entry forms in page format or grid layout format.
You can add, edit, or delete records in any table using Visdata. You can connect
to Microsoft Jet versions 1.1, 2.0, or 3.0 databases, as well as versions of dBASE,
FoxPro, and Paradox. You can even access data from Excel spreadsheets, delimited
text files and ODBC-connected databases. Visdata is a great tool for building sample
tables and entering test data for your Visual Basic 5 applications. It is also a
good tool for compacting, repairing, and managing user and group access rights for
Microsoft Jet databases.
Visdata allows you to test SQL queries and save them in your Microsoft Jet database
as stored queries that you can access from your Visual Basic 5 programs. You can
also use Visdata to copy records from one table to another--even to copy whole data
tables from one database to another. This capability gives you the power to create
backups of selected information from your existing databases.
Finally, you can use Visdata to inspect the properties of Microsoft Jet data objects
such as fields, relationships, tables, and indexes. You can learn a great deal about
how the Microsoft Jet database engine operates by using Visdata to peek under the
hood to see the heart of the Visual Basic 5 data access engine.
The Visdata Opening
Screen
If you don't already have Visdata running, start it now. You can start Visdata
by selecting Visual Data Manager... from the Add-Ins menu. Once started, select File
| Open Database... | Microsoft Access..., and then open the BOOKS5.MDB database
that shipped with the CD included with this book. Your screen should look like Figure
7.1.
Figure
7.1. The Visdata main screen.
This MDI form is "Data Central" for the Visdata application. All database
activity starts from this screen. Four major components of this screen deserve attention:
- The Main Menu: This menu gives you access to all the features of Visdata. This
menu also expands once you open a database.
- The Database Window: This window shows all the properties and table objects present
in the database you currently have open.
- The SQL Statement Window: This window allows you to write and execute standard
SQL statements against the database you currently have open.
- The Toolbar: You use this to determine the type of data objects you want to work
with.
Now let's go through each of the four components of the Visdata main screen in
a bit more depth.
The Main Menu
The Visdata Main Menu contains four menu items: File, Utility, Window, and Help.
The Utility menu item is enabled once a database is opened.
The Visdata Main Menu gives you access to all the features and options of the
program. You'll learn each menu option in depth later, but first, let's explore the
File menu options just a bit.
The File | Open Database... option, which we used in the preceding section, allows
you to open an existing database. This database can be any one of several formats.
The most common database format you'll probably deal with is the Microsoft Jet format
(also known as the Microsoft Access database format). For practice, let's use Visdata
to open an existing Microsoft Jet database.
Select File | Open Database... | Microsoft Access. The Visdata program presents
you with an Open Microsoft Access Database dialog box (see Figure 7.2).
Figure
7.2. Opening a Microsoft Access database.
Locate and select the BOOKS5.MDB database that can be found in the \TYSDBVB5\SOURCE\DATA
directory on the CD that ships with this book. Click the Open button to load the
database. Once the database is loaded, Visdata updates the Database window to show
all the primary data access objects in the currently opened database. Your screen
should now look something like Figure 7.3.
You can close the database by selecting File | Close from the Visdata main menu.
The Database Window
The Database window shows all the major data access objects in the currently opened
database. The Database window is where you go to add new tables to the database and
modify the design of one of the current tables. You can also open existing data tables
to add records to them. If you click the alternate mouse button within the Database
window while you have a table highlighted, you see several other table management
options.
Figure
7.3. Visdata with an open database.
NOTE: We use the term "alternate mouse button"
to avoid any confusion between left-handed and right-handed users. If you have your
mouse set for left-handed use, the alternate button is the left button; if you have
your mouse set for right-handed use, the alternate button is the right button.
Properties The Properties object shows the various properties of the opened database.
With the BOOKS5.MDB database open, click the + sign next to the Properties
object. Your screen should look like Figure 7.4.
NOTE: Many of the properties listed on this screen
are available only in the Version 3.0 Microsoft Jet MDB format. Don't be alarmed
if your screen has several empty fields. You learn more about the difference between
the various MDB formats later.
Figure
7.4. Viewing the database properties.
Open The Open alternate mouse option loads the selected table. It performs the same
function as double-clicking the table name. Design The dDesign option brings up the
table Structure design dialog. You can view, edit, and add fields and indexes from
this screen. Try this with a few tables so you can get a feel for the information
available in the Design dialog. Rename The Rename option allows you to rename the
highlighted table without deleting the data. Highlight the Authors table by clicking
it once with the primary mouse button. Now click the alternate mouse button to bring
up the context menu. Select Rename from the menu and enter MoreAuthors as the new
name, and then press Enter. Your screen should look like Figure 7.5 as you rename
the Authors table.
Before you continue with the project, change the MoreAuthors table back to Authors
using the same technique previously described. Delete The Delete option lets you
delete the highlighted table and all its contents. To delete a table and all its
contents, select the table you want to delete and click the alternate mouse button.
Select the MoreAuthors table and click the alternate mouse button to bring up
the context menu. Select Delete from the list. Click Yes at the confirmation dialog
message to delete the MoreAuthors table. Your window list refreshes automatically.
Figure
7.5. Renaming a data table.
Copy Structure The Copy Structure... option lets you copy the highlighted table's
field layout and design, with or without existing data, to a different database.
Select the Authors table and click the alternate mouse button to bring up the context
menu. Select Copy Structure... from the menu list, and you see a dialog box like
the one in Figure 7.6.
Figure
7.6. Copying a table.
Notice that you can enter a new database name and connect string in the dialog box.
This capability means you can copy the structure to an entirely different database.
Leave the database name and connect string alone for now. Check the Copy Indexes
and Copy Data checkboxes, click on the Authors table in the Table list box, and click
OK. You are then prompted for a table name. Enter MoreAuthors and click OK. A message
from Visdata appears, telling you that the new table has been created. When you exit
the dialog by clicking Close, Visdata refreshes the Window List automatically. You
should now see a new table in the list--MoreAuthors. Refresh List The Refresh List
option updates the window to reflect changes in the data access objects that are
part of the database. Usually, Visdata refreshes the Database window each time you
take an action that affects the contents of the list. Some actions, however, do not
automatically update the window. For example, if you use the SQL window to enter
SQL statements to create a new data table in the database, Visdata does not automatically
refresh the Database window.
To refresh the Database window, simply click anywhere in the Database window,
and then click once with the alternate mouse button to bring up the context menu.
Select Refresh List from the list. Visdata refreshes the Database window to reflect
the current state of the data access objects in the opened database. New Table This
option displays the Table Structure dialog, which can be used to construct a new
table or index. We work on building new tables in the section entitled "Adding
Tables and Indexes to the Database" later in this chapter. New Query This option
displays the Visdata Query Builder, which can be used to help build SQL statements.
We discuss the Query Builder when describing the Utility menu later in this chapter.
The SQL Statement
Window
The SQL Statement window enables you to enter and execute standard SQL statements
against the opened database. You can save the SQL query for later use in your Visual
Basic 5 programs.
Select the SQL Statement window by clicking the top border of the window one time.
Now enter the following SQL query into the text window:
SELECT * FROM Authors
Now, make sure that the Use DBGrid Control on New Form icon, located at the top
of the Visdata window, is selected, and then select the Execute button in the SQL
Statement window to run the query. This is not an SQL Passthrough query, so answer
No when prompted with this question.
This statement selects all the data in the Authors table and presents it to the
screen. Your screen should look like the one in Figure 7.7.
Figure
7.7. Results of an SQL query.
NOTE: We will cover SQL SELECT queries in depth
in the lesson on Day 8, "Selecting Data with SQL." For now, just remember
that you can write, test, and save your SQL queries using the Visdata SQL window.
You can save this query for later use within your Visual Basic 5 programs by first
closing the screen that contains the result of your Select query and then clicking
on the Save button in the SQL Statement window. Next, supply the query object name
qryTest, and click OK in the dialog box that appears (see Figure 7.8). Again, this
is not an SQL Passthrough query, so answer No when the SQL Passthrough dialog appears.
Each time you load Visdata, the program remembers the last SQL query you entered
in the SQL window. You can click the Clear button to clear out the text in the SQL
Statement window.
The Toolbar Buttons
Icons appear on a toolbar near the top of the Visdata main screen. You use these
icons to establish the type of data object Visdata uses to access the data and the
type of data entry form Visdata uses to present the selected data on the screen.
You can also use these icons to assist in making changes to your database, with the
option of committing the changes once made or rolling back (undoing) the change.
Figure 7.8. Saving a query.
Selecting the Default Data Access Object The first set of icons controls the type
of data access object that Visdata uses to open the data table. The default data
access object is the Visual Basic 5 Dynaset, the most flexible Visual Basic 5 data
access object. You can use the Dynaset object to create updatable views of more than
one table or open an existing table for read/write access.
You can also use the Snapshot data access object to open a read-only view of one
or more data tables. Snapshot objects are faster than Dynasets, but require more
workstation memory.
Finally, if you only need access to the physical base table in the database, you
can select the Table radio button. Tables are fast and require little workstation
memory. The disadvantage of the Table data access object is that you cannot use it
to combine two or more tables into a single view.
Even though most of the work you do from Visdata is with base tables, you should
set this radio button to use the Dynaset data access object. Dynasets are fast enough
for almost all Visdata work and they provide the most flexibility when dealing with
multitable views. Selecting the Default Data Form The second set of icons enables
you to select the type of data form you see when you load your data access object.
Visual Basic 5 now ships with a very nice data-bound grid tool. This grid automatically
loads all the fields in the selected data access object and scrolls data records
into the table as needed. This grid object may be the most useful selection of the
three. Click the Use DBGrid Control on New Form icon to make this your default data
form.
The other two icons select two versions of a standard data entry form. The first
icon, Use Data Control on New Form, loads the records from the data access object
one at a time, using the Visual Basic 5 data control tool. The second icon, Don't
Use Data Control on New Form, presents a similar form, but without using the Visual
Basic 5 data control tool. The advantage of the Data Control form is that it handles
BIT and BINARY data type fields better than the No Data Control form. The No Data
Control form, however, allows users to press F4 to display the entire contents of
a data field whose contents overflow the control's display area. This zooming feature
is handy when dealing with large text fields or memo fields.
You can switch the Form Type radio button after each table is opened and displayed,
which enables you to open one or more tables using different data forms. Let's open
three tables, each using a different data form.
First, select the Use DBGrid Control on New Form icon from the toolbar. Now double-click
the Authors table. This action brings up the Authors table in a grid display. Your
screen should look like Figure 7.9.
Figure
7.9. Authors table using the grid data
form.
NOTE: Please note that the columns in this view
can be resized. Simply select a column divider with your mouse and drag to the desired
width.
Next, select the Use Data Control on New Form button and double-click the Authors
table again. Now you see the same data presented in a standard data entry from. Your
screen should now look like Figure 7.10.
Figure
7.10. Authors table using the Data Control
form.
Next, select the Don't Use Data Control on New Form icon and double-click the Authors
table a third time. Now, you see the Authors data presented in a slightly different
data entry form. Notice the differences in the way the Contracted field appears on
the Don't Use Data Control on New Form (as text) form and the Data Control form (checkbox).
Figure 7.11 shows a tiled view of the three data forms side by side.
Figure
7.11. Three data forms side by side.
Beginning, Rolling Back, and Committing Transactions A basic principle in database
management is the concept of begin, rollback, and commit transactions. This refers
to the theory that changes are temporarily made to the database and reviewed before
they are made permanent. If an error occurs as a result of the temporary change,
the transaction can be undone, or rolled back without causing permanent damage to
the underlying data. This is a particularly handy concept when making large changes
to multiple data tables. We address this issue in detail in Day 17, "Multiuser
Considerations."
To use this concept in Visdata, simply select the Begin a Transaction icon before
you make a change to your database. If you like the change, select the Commit current
Transaction icon and the change becomes permanent. If you don't like the change,
press the Rollback current Transaction icon to undo the changes.
Please note the use of the word "current" in the Commit and Rollback
operations. This refers to all changes made since the last time the Begin icon was
selected. Transactions cannot be rolled back once they are committed.
Now that you have seen the major components of the Visdata main screen, let's
review each of the menu items in greater detail.
The Visdata File
Menu
The Visdata File menu contains nine items. You can open, create, and close databases
from the file menu, import and export data from and to the open database, log into
a designated workspace, and review any errors that have been logged since you started
Visdata. You can compact or repair Microsoft Jet databases from the File menu. You
also exit the program from the File menu.
If you have used Visdata before, you'll also see a list of the most recently used
databases in this menu. You can reload one of those databases by clicking its name
in the File menu.
Open Database
Before you can begin working on an existing database, you must first load it using
the Open Database... menu option. This menu option enables you to load one of several
database formats. Each format has a slightly different set of options in the menu
tree. You can load Microsoft Access, dBASE, FoxPro, Paradox, Excel, text files, and
ODBC data sources.
NOTE: You can load only one database at a time
into Visdata. If you need to work on tables from more than one database, you need
to use the Utility | Attachments... menu option to attach the foreign data tables
(the tables that are contained within a database other than the one on which you
are working) to the database you currently have open. We cover the Attach option
later in this lesson.
When you select Open Database..., you see several other menu choices. You select
one of the secondary items depending on the database format you want to access. The
following sections cover each of the secondary menu choices and how you use them
to open existing databases. Microsoft Access When you select the Microsoft Access...
option, Visdata brings up a File Open dialog box and prompts you to select the Microsoft
Access database you wish to load (see Figure 7.12).
Figure
7.12. Loading a Microsoft Access database.
dBASE (III, IV, and 5.0) You can also use Visdata to load dBASE-format databases.
When you select the dBASE menu option, you see an additional menu that asks you to
select version III, IV, or 5.0 database format.
WARNING: You must tell Visdata what dBASE format
you are loading so that it knows what index files and memo field formats to expect.
If you load an incorrect format into Visdata, you do not see an error message right
away. You may receive error messages, however, when you attempt to read or write
data to the database. These errors may permanently corrupt your database. Be sure
you load the FoxPro and dBASE databases using the correct menu option to avoid problems.
When you select the correct format, you see the File Open dialog box prompting
you to locate and load a database. After the database is loaded, you see the list
of available tables. You also see a message at the bottom of the screen suggesting
that you use the Attach option to access the dBASE format data tables (see Figure
7.13).
Figure
7.13. Viewing a loaded dBASE database.
TIP: When you deal with non-Microsoft Jet data
formats, you get better performance speed if you access them through the Utility
| Attachments... menu option. We cover the Utility | Attachments... menu option later
in today's lesson.
FoxPro (2.0, 2.5, 2.6, and 3.0) Loading the FoxPro format databases works the
same as loading the dBASE format databases. When you select FoxPro from the menu,
you see an additional menu list that asks you to select the proper database format.
When you select the format, you see the File Open dialog prompting you to locate
and load the proper database. The same warnings mentioned in the preceding dBASE
section apply here. Do not attempt to load a FoxPro 2.6 format database using the
FoxPro 2.5 format menu option. Even if the file loads initially without errors, you
will probably get unpredictable results and may even corrupt your database. Paradox
(3.x, 4.x, and 5.0) Opening Paradox files with Visdata works much like opening FoxPro
or dBASE format databases. You select the database version you wish to access, and
then fill out the File Open dialog box to locate and load the database. The CD that
ships with this book contains a Paradox 4.x format database called PDSAMPLE.DB.
You can locate and load this file from the \TYSDBVB5\SOURCE\DATA\PARADOX
directory. Excel Visdata can also directly load Microsoft Excel spreadsheet files
and enable you to manipulate their contents. When you select Excel... from the Open
Database menu, you see the File Open dialog box that prompts you to locate and load
the Excel spreadsheet.
Visdata locates all sheets and named ranges defined in the Excel file and presents
them as table objects in the Database window (see Figure 7.14).
Figure
7.14. Using Visdata to directly load an
Excel spreadsheet.
Figure 7.15 shows the sample Excel spreadsheet \TYSDBVB5\SOURCE\DATA\XLDATA\EXSAMPLE.XLS
as it appears in Excel. The range name box is opened in the illustration so that
you can see how the range names in Excel compare to the table names in Visdata.
Figure 7.16 shows the same Excel file opened using Visdata. In Figure 7.16, the
table object Sheet1$ has been opened as a Dynaset object.
WARNING: Visdata opens Excel data files for exclusive
use only. If you have an Excel spreadsheet open with Visdata, no other program on
your workstation, or any other program on the network, can open the same spreadsheet.
If some other program has an Excel spreadsheet open, you cannot open it using Visdata
until the other program closes that file.
After you open the Excel file, you can perform all data entry operations on that
file including creating new tables and editing data in existing tables in the spreadsheet.
Figure
7.15. Viewing CH0702.XLS with
Excel.
Figure
7.16. Viewing CH0702.XLS with
Visdata.
Text Files Visdata can load various standard formats of ASCII text files for read-only
access. When you select a file to load (using the File Open dialog box), you actually
open the entire directory as a database. Visdata permits you to select any file with
a .TXT extension from the Database window and open it as a read-only data table.
Figure 7.17 shows the file \TYSDBVB\SOURCE\DATA\TEXT\TXSAMPLE.TXT opened
as a read-only data file.
Figure
7.17. Opening a text file with Visdata.
Visdata recognizes several types and formats of ASCII text files. The default format
is comma-delimited fields with character fields surrounded by quotes. ODBC The ODBC...
menu option is slightly different from the previously discussed Open commands. This
option enables you to use Visdata to open predefined ODBC data sources. When you
select the ODBC... menu option, you see a screen that asks you for the data source
type, data source name, user ID, and password for that data source (see Figure 7.18).
After you fill out the ODBC dialog box, Visdata locates and opens the data source
and updates the Database window.
Figure
7.18. Using Visdata to open an ODBC data
source.
Before you can open an ODBC data source, you must first define that data source using
the ODBC program from the Control Panel. You learn about defining and accessing ODBC
data sources in depth in Week 3. If you want more information on defining ODBC data
sources, you can refer to the help available when you load the ODBC programs from
the Control Panel.
New...
The New menu option enables you to use Visdata to create entirely new databases
in several formats. This section concentrates on the Microsoft Access database format.
Most of the rules for creating Microsoft Jet databases apply equally to non-Microsoft
Jet formats. Although the Visdata application can create a non-Microsoft Jet database,
you should not use Visdata to create non-Microsoft Jet databases very often. If you
need to work in non-Microsoft Jet formats, use the native database engine to create
the data files. You can then use Visdata to access and manipulate the non-Microsoft
Jet databases. Access (Version 2.0 and 7.0) When you select the Microsoft Access
menu item, Visdata asks you to select one of two versions of Microsoft Access data
format: 2.0 or 7.0. The 2.0 format can be read by all versions of Microsoft Access
and by Microsoft Visual Basic versions 4.0 and later. Version 7.0 format databases
can only be read by the 32-bit version of Visual Basic 4 and by the 32-bit version
of Microsoft Access. The advantage of the older formats is that the data can be read
by most versions of the software. The advantage of the version 7.0 format is that
it allows for additional database properties that are not available in the older
formats.
WARNING: Attempting to read a version 7.0 Microsoft
Access database with Access version 2.0 or Visual Basic version 3.0 results in an
error that tells you your database is invalid or corrupt. If you know that you will
be
working only with software that can read version 7.0 files, you should select
the version 7.0 format because it provides additional features. If, however, you
plan to deploy your database in an environment that contains both 16- and 32-bit
versions of the software (you use Visual Basic 3, or 16-bit Visual Basic 4), you
should stick with the version 2.0 data format.
After you select a database format from the submenu, Visdata presents you with
a dialog box that prompts you to enter a filename for the new database (refer to
Figure 7.19).
Figure
7.19. Creating a new Microsoft Access
database.
Creating a new database does not automatically create data tables; you must use the
New command button in the Database window to create a new table. dBASE, FoxPro, and
Paradox Creating dBASE, FoxPro, and Paradox format databases is similar to creating
Microsoft Access databases. When you select one of these formats, you are prompted
to indicate the exact version of the database you want to create. After you select
a version, Visdata presents you with a simple dialog box that prompts you to enter
a name for the database. This name is not a data file; it is a file directory (called
a folder in Windows 95). You can include any valid drive designator and directory
path you want when you create the database. See Figure 7.20 for an example of creating
a FoxPro database directory.
WARNING: Remember that Visdata creates directories
(or folders), not data files, when you create dBASE, FoxPro, or Paradox databases.
Be sure to use names that make sense as directories or folders.
Figure
7.20. Creating a FoxPro database directory.
Text You can use Visdata to create text data files. These files are comma-delimited
ASCII text files that you can open for read-only access from Visdata. Even though
you can create the database files and tables, you cannot add any data to the tables
or create indexes on the data tables. This might be useful if you want to create
ASCII text data files for use by other applications.
When you select the text menu option, Visdata prompts you to enter a name for
the database. This name is used to create a directory (Windows 95 folder) on the
designated drive. You can use any valid device designator and directory path you
want when you create the database.
Close Database
The Close Database menu option simply closes the open database. All tables are
closed at the same time.
Import/Export...
The Import/Export... function allows you to move data into and out of the currently
open database. To bring data in from another database, simply select Import/Export...
from the File menu. When this option is selected, you are presented with the dialog
shown in Fig- ure 7.21.
Figure
7.21. The Import/Export dialog.
Next, select the Import command button. You are requested to select the database
format from which to extract data. See Figure 7.22 for details.
Figure
7.22. The Import Data Format selection.
Select your database format and select OK. You are then presented with a dialog that
allows you to select a data table to import from the database you selected in the
preceding step. (See Figure 7.23.)
Figure
7.23. Selecting a table to import.
Select the desired table and select the Import button to move the data into the currently
open database.
To export data, select Import/Export... from the File menu. Then, select the table
from the dialog that appears and press the Export Table(s) button. You are then prompted
to select a format and a file to hold the exported data.
Workspace
The Workspace menu item displays a login dialog that allows you to log in to the
currently open database as a different user. This is handy if you want to test user
IDs and passwords. When you select Workspace from the menu, you see a dialog box
that requests a login ID and password (see Figure 7.24).
Figure
7.24. Viewing the Login dialog.
Workspace data objects are covered in detail on Day 10, "Creating Database Programs
with Visual Basic Code."
Errors
The Errors menu option shows the last error or set of errors reported to Visdata
(see Fig- ure 7.25).
Figure
7.25. Viewing the errors collection.
Some data sources return more than one error message per transaction (usually ODBC
data sources), which is referred to as the errors collection. This menu option lets
you review the errors collection in a grid listing. If no errors have been returned,
this grid is empty.
TIP: Even if you have had several successful
database transactions since your last error, the most recent error remains in this
grid display.
Compact MDB...
You can use Visdata to compact existing Jet databases (MDB files). Compacting
a database removes empty space in the data file once occupied by records that were
deleted. Running the Compact menu option also reorganizes any defined indexes stored
in the database.
When you select Compact MDB..., you have to select a database format. If you select
3.0 MDB... from this menu, the database you selected is compacted and stored as a
Microsoft Jet version 3.0 database. If you select 2.0 from this menu, the database
you select is compacted and stored as a Microsoft Jet version 2.0 database.
NOTE: Although not recommended, you can use the
Compact Database menu option to convert older database formats to newer ones, but
you cannot use the Compact Database menu option to convert newer formats to older
ones. For example, you cannot convert a 3.0 Microsoft Jet database to a 2.0 Microsoft
Jet database.
When you select the target format, you see a File Open dialog box asking you to
select the database you want to compact. The database you select cannot be opened
by any other program while it is being compacted. After you select the source database,
you have to enter the name of the destination database file. If you select the same
name as the source, your current data file is overwritten with the new format. If
you select a new database filename, all information is copied from the source database
to the target database.
WARNING: Even though Visdata allows you to compact
a database file onto itself, this practice is not recommended. If anything happens
midway through the compacting process, you could lose some or all of your data. Always
compact a database to a new database filename.
Before Visdata compacts your database, you will be asked if you want to encrypt
the data. If you say Yes, Visdata copies all data and encrypts the file so that only
those who have access to the security files can read the data. We talk more about
data encryption on Day 21 "Securing Your Database Applications."
Repair MDB...
If you get a "database corrupt" error when you attempt to open a Microsoft
Jet database file, you may need to repair your database. Database files can become
damaged due to power surges during read/write operations or due to physical device
errors (damaged disk drive plates, and so on). You can repair an existing database
by selecting Repair MDB... from the File menu. You then see a File Open dialog box
that asks you for the database filename. Once you select the filename, Visdata loads
and repairs the database to the best of its capabilities. Unfortunately, you may
receive a message saying some of the data could not be recovered.
TIP: Remember to make copies of your database
on a regular basis. You should not depend on the Repair routine to recover all your
data. If you experience a program crash due to corrupted data, you can always restore
the file from the most recent backup. You should also use the Windows 95 or DOS defragment
utility on your hard drive after performing a Compact or Repair function to improve
the overall performance of your application.
Exiting Visdata
The Exit item does just what you expect. When you exit Visdata, your current database
closes, along with all open database objects. If you have text in the SQL window,
it is saved and restored the next time you load Visdata. Visdata also remembers the
windows you had open, as well as their sizes and their locations for the next time
you load Visdata.
Adding Tables and
Indexes to the Database
When you have created a new database, you can add new tables and indexes to the
database. You can also add new tables and indexes to existing databases. To illustrate
the process of managing database tables using Visdata, let's create a new Microsoft
Access (Jet) database, add a new table, add a new index, and then modify the table
structure.
Creating the New
CH07NEW.MDB Database
If you haven't already done so, load and start Visdata. Select File | New... |
Microsoft Access... | Version 7.0 MDB... from the main menu and enter CH07NEW.MDB
in the Select Microsoft Access Database to Create dialog box (see Figure 7.26). Click
the Save button to create the new database.
Figure
7.26. Creating CH07NEW.MDB.
Adding a New Table to the Database
To add a new table to the database, click the alternate mouse button in an open
space of the Database window and select New Table to bring up the Table Definition
dialog box. Your screen should look like Figure 7.27.
Figure
7.27. Defining a new table.
Enter NewTable in the Table Name field at the top of the dialog box. Now you can
add fields to the data table. Click the Add Field command button to bring up the
Add Field dialog box. Your screen should look like Figure 7.28.
Figure
7.28. Adding a new field to the table.
Enter the field name Field1. Set the type to Text and the Size to 10. Notice that
you can set default values and validation rules here, as well. We'll cover these
properties on Day 9, "Visual Basic and the Microsoft Jet Engine."
After you have entered the information you need to define the field, click the
OK button to save the field properties to the database.
WARNING:: Be sure you click the OK button after
each field you define. If you just fill out the dialog box and then click the Close
button, the information you entered on the form won't be saved to the database.
Now that you have defined Field1, let's define one more field. Enter Field2 as
the name, and select Currency as the Field Type. Notice that you cannot set the field
size. Only Text type fields allow you to set a field size. Now click the OK button
to save this field definition; then exit the field definition dialog by clicking
the Close button. The Table Structure dialog box should now show two fields defined.
Refer to Figure 7.29 as a guide.
Figure
7.29. Table Structure with two fields
defined.
Editing an Existing Field
When you return to the Table Structure screen, notice that the same set of properties
you saw in the Add Field dialog box appears to the right of the Fields list. You
can edit some of these values for the field by highlighting the field in the list
on the left and editing the dialog values on the right. Make Field2 required by selecting
the Required checkbox at the right side of the dialog box.
Building the Table
Before you leave this screen, you must first click the Build Table button to actually
create the table in your database. Up to this point, Visdata has stored the data
table and index definitions in memory. Clicking the Build the Table button is the
step that actually creates the data table.
WARNING: If you click the Close button before
you click the Build the Table button, you lose all your table definition information.
You have to enter all the table definition data again before you can build the new
table.
When you add data to an existing data table, you cannot use Visdata to modify
the table structure. You must first remove all records from the data table before
you can make any modification to the structure. You can, however, add new fields
to a table after data has been entered.
Adding a New Index
to the Database Using the Design Button
You can add indexes to existing tables by selecting the table, clicking the alternate
mouse button, and selecting Design... from the menu that appears. This option brings
up the same input form you used to add fields to the database. Now let's add a Primary
Key index for the NewTable you just created.
WARNING: Even though Visdata allows you to enter
New Index information during the New Tables process, you cannot build a new table
and a new index for the same table at one time. Visdata must see the data table that
already exists before it can create an index for that table. Use the Design mode
of the Table Structure dialog box to add indexes to existing tables.
Click the Add Index command button to bring up the Add Index dialog box. Enter
PKNewTable as the index name. Click Field1 in the field list to make that field the
source of the Primary Key index. Your screen should look like Figure 7.30.
Be sure to click the OK button to add the index definition to the database. When
you have added the index definition, click Close to exit the dialog. Your screen
should now look like Figure 7.31.
Figure
7.30. Adding a new index to the database.
Figure
7.31. The Table Structure dialog after
adding a new index.
Printing the Table Structure
While you are in the Design mode of the Table Structure dialog, you can click
the Print Structure button to get a hard-copy printout of the selected table and
index objects you have defined. Visdata sends the information directly to the default
printer defined for Windows and does not prompt you for any options. Please note
that the Print Structure button does not appear when creating a New table; it appears
only when you select Design after the table has been created.
TIP: If you want to save the structure to a file,
you can use the printer applet in the Control Panel to define a printer as a file,
and then set that print device as the default printer before you click the Print
Structure button in Visdata. Be sure to reset your default printer after you send
your table structures to a disk file.
The Visdata Utility
Menu
The Visdata Utility menu contains several options to help you manage your data
tables. You can create, test, and save query objects using the Query Builder; build
data entry forms with the Data Form Designer; perform global replace routines on
existing data tables; define attachments; define security; and define system preferences.
Query Builder...
The Query Builder serves as a good tool for testing queries and then saving them
to the database as query objects. You can later access these objects from your Visual
Basic 5 programs. The Query Builder enables you to perform complex queries without
having to know all the details of SQL syntax.
NOTE: We cover SQL SELECT queries in
detail on Day 8, "Selecting Data with SQL." For now, if you are not familiar
with SQL statements, just follow along with the example. The important thing to remember
is that you can use the Visdata Query Builder to create, test, and store SQL queries.
Let's build a query, test it, and save it in a database. First, make sure you
have BOOKS5.MDB open (found in the TYSDBVB5\SOURCE\DATA directory
on the CD included with this book), and then select Utility | Query Builder... from
the main menu. You see a data entry form ready for your input (see Figure 7.32).
You have several options on this screen. It's easy to get confused if you are
not quite sure of what to look for. Instead of going through all the possible options
for a query, this example goes step-by-step through a rather simple SELECT
query and its results. Table 7.1 shows the values to select and Figure 7.33 shows
the completed form. Refer to these items as you build your query.
Figure
7.32. Using the Query Builder.
Figure
7.33. The completed query.
Be sure to set the values in the screen in the order they appear in Table 7.1. After
you enter the Field Name, Operator, and Value settings, click the And into Criteria
button to force the settings into the Criteria box at the bottom of the window.
Table 7.1. Building a query.
| Property |
Setting |
| Tables |
BookSales |
| Field Name |
BookSales.Units |
| Operator |
> |
| Value |
14 |
| Fields to Show |
BookSales.Title |
|
BookSales.Units |
| Order by |
BookSales.Units, Desc |
After you have entered all the values, click Save and enter qryTest at the dialog
prompt. You have just saved the query for future use. Now try running it. Click Run
to get Visdata to execute the query. Click No when Visdata asks you if this is an
SQL Passthrough query. Visdata then executes the query and displays the results on
your screen, as shown in Fig- ure 7.34.
Figure
7.34. Results of the executed query.
Data Form Designer...
The Data Form Designer builds a data entry form complete with a data control and
command buttons for data administration. The form is saved to the currently active
Visual Basic project. To demonstrate, let's build a sample form with the Data Form
Designer.
First, make sure you have the BOOKS5.MDB (TYSDBVB5\SOURCE\DATA)
database open in Visdata. Next, select Data Form Designer... from the Utility Menu.
You should see the Data Form Designer dialog (see Figure 7.35).
Figure
7.35. The Data Form Designer.
Enter frmAuthors in the Form Name field. Next, select Authors as the RecordSource.
Note, when you select Authors, all of the fields within that table appear in the
Available Fields list box. Now, click the >> button to move all the fields
into the Included Fields list box. Your dialog should look like Figure 7.36.
Figure
7.36. The completed frmAuthors design.
Click the Build the Form button to save the form to the currently active Visual Basic
5 project.
Now, close the Data Form Designer and Visdata and return to your Visual Basic
5 project. Open frmAuthors. You should see a form similar to the one in Figure 7.37.
Figure
7.37. The completed frmAuthors form.
Notice how you have all the data fields, as well as a data control and command buttons.
This is a quick and easy way to build forms for data entry!
Global Replace...
The Global Replace menu option enables you to perform a mass update of existing
tables, which comes in handy when you need to zero values in test data or need to
perform mass updates on a database.
For this example, set all the fields in a data table to the same value. Load the
BOOKS5.MDB database (TYSDBVB5\SOURCE\DATA), and then select Utility
| Global Replace... from the menu. You see the Global Replace dialog box, as shown
in Figure 7.38.
Figure
7.38. Entering a Global Replace command.
Select the NewAuthors table and the Contracted field. Set the Replace With value
to zero and leave the Criteria field blank. When you click the OK button, Visdata
resets all the NewAuthors.Contracted fields to zero. You can limit the number of
records affected by the Global Replace command by entering an appropriate logical
statement in the Criteria box. For example, if you wanted to update only the records
that have an Au_ID value of 30, you could enter the following line in the Criteria
box:
Au_ID=30
We cover Criteria more in depth in the lesson on Day 8, and you'll learn more
about the global replace command in the lesson on Day 14, "Error Handling in
Visual Basic 5.0."
Attachments...
Visdata allows you to attach external database files to an existing Microsoft
Access (Jet) format database. When you create an attachment, you actually create
a link between your own Microsoft Access database and another database. You don't
actually import any data from the external database into your own MDB. By creating
attachments, you can access and manipulate external data files as if they are native
Microsoft Access tables. Attached tables appear in the Database window as local table
objects in your database, even though they are only links to external data files.
TIP: Not only is the attachment method convenient,
it provides the fastest way to access external data using Visual Basic 5 programs.
You can load, index, and display attached external tables faster than you can if
you use ODBC or directly open the external data files in their native format.
Now create an attached table in the BOOKS5.MDB database that we used
earlier today.
If you like, you can create an attachment to any other Microsoft Jet format database
you already have on hand.
First, if you don't have it loaded already, select File | Open Database... from
the main menu to load the BOOKS5.MDB (TYSDBVB5\SOURCE\DATA) database.
Then select the Utility | Attachments menu option. You will see a grid that shows
all the current attachments for this database. Because there are no attachments to
this database, this box should be empty. Click the New command button to open the
New Attached Table dialog box. Your screen should now look like Figure 7.39.
Figure
7.39. Adding an attachment to a Microsoft
Access database.
Table 7.2 shows the information you should enter into the Attachment dialog box.
Table 7.2. New Attached Table dialog box values.
| Dialog Field |
Value |
| Attachment Name |
Test Attachment |
| Database Name |
\TYSDBVB5\SOURCE\DATA\CRYSRPT.MDB |
| Connect String |
Access MDB |
| Table to Attach |
CompanyMaster |
If you are attaching to a data source that requires a password in the connect string,
you could check the AttachSavePWD checkbox to prevent a login dialog each time you
open the database. If you want to create an exclusive attachment, you could check
the AttachExclusive checkbox. Leave both of these fields blank for now.
After filling out the dialog form, click Attach to commit the attachment. After
you close the Attachment dialog box, you see that the grid is updated to show the
new attachment you just added to the database. Close the New Attached Tables dialog
and the Attachments grid. You now see a new entry in your Database window list. This
shows a new table object. Note how the icon for the attachment differs from the other
tables' icons. Your screen should look something like the one in Figure 7.40.
Figure
7.40. An attached table object.
You can now access this attached table just like you would any table you created
using Visdata.
Groups/Users...
Selecting Utility | Group/Users... brings up the Groups/Users/Permissions dialog
shown in Figure 7.41.
Figure
7.41. The Groups/Users/Permissions dialog.
This dialog can be used to set all of the permission rights for users and groups.
In order to use this function, you must have a security file (SYSTEM.MD?)
to which you belong. This function allows the setting of rights and passwords on
a user and on a group level.
SYSTEM.MD?
Use the SYSTEM.MD? menu option to locate and load the SYSTEM.MD? security
file. The SYSTEM.MD? file contains information about Microsoft Access file
security, including defined users, groups, workspaces, passwords, and data object
rights. You must create this file using the Microsoft Access utility WRKGADM.EXE.
The Utility | SYSTEM.MD? menu option presents you with a File Open dialog so that
you can locate and load a SYSTEM.MD? file. Once it is loaded, Visdata adds
this information to the Registry so that you won't have to reload it in the future.
Preferences
The Preferences menu option lets you customize the way Visdata shows you information.
Two toggle settings control the way Visdata displays data, and two parameter settings
control the way Visdata performs database logins and queries. Open Last Database
on Startup When you toggle on the Open Last Database option, Visdata remembers the
last database you had open when you last exited Visdata and automatically attempts
to open that file the next time you start Visdata. Include System Files When you
toggle on the Include System Files option, you see several tables maintained by Microsoft
Jet to keep track of table, user, group, relation, and query definitions. Users cannot
access these tables, and the tables should not be altered or removed at any time.
Query Time-Out Value You can use the Query Time-Out Value menu option to adjust the
number of seconds Visdata waits before reporting a time-out error when attempting
a query. If you work with slow external data files or ODBC connections, you can adjust
this value upward to reduce the number of errors Visdata reports when you run queries.
Login Time-Out Value You can use the Login Time-Out Value menu option to adjust the
number of seconds Visdata waits before reporting a time-out error when attempting
to log into a remote data source. Adjust this value upward if you get time-out errors
when dealing with slow ODBC or external data sources.
The Visdata Windows and Help Menus
The last two items on the Visdata main menu are the Windows menu and the Help
menu. These two items contain the usual options that all good Windows programs have.
The Windows Menu
This menu helps you control how all the child windows are displayed within the
main MDI form. You can Cascade, Tile, or Arrange Icons from this menu. You can also
force the focus to one of the three default Visdata windows: Database window, SQL
window, or MDI form.
The Help Menu
The Help menu gives you access to the Visdata Help file included with your version
of Visual Basic 5. You can also view the About box from this menu.
Summary
Today you learned how to use the Visdata sample application to perform all the
basic database operations needed to create and maintain databases for your Visual
Basic 5 applications.
You learned how to do the following:
- Open existing databases.
- Create new databases.
- Add tables and indexes to existing databases.
- Attach external data sources to existing Microsoft Access databases.
- Access data using the three data access objects: Table, Dynaset, and Snapshot.
- View data on-screen using the three data forms: form view with the data control;
form view without the data control; and grid view using the data-bound grid.
- Build and store SQL queries using the Query Builder.
You learned to use Visdata to perform database utility operations, including the
following:
- Copying tables from one database to another
- Repairing corrupted Microsoft Access (Jet) databases
- Compacting and converting versions of Microsoft Jet databases
- Performing global replace operations on tables
You learned to use Visdata to adjust various system settings that affect how Visual
Basic 5 displays data tables and processes local and external database connections
and parameters that control how Visual Basic 5 locks records at update time.
Quiz
- 1. Where can you find a copy of the Visdata source code?
2. How do you copy a table in Visdata?
3. When do you need to Refresh the Tables/Queries window?
4. Can you manipulate spreadsheet data with Visdata?
5. What information can be obtained from the Properties object in the Database
window?
6. Why would you compact a database?
7. Can you compact a database onto itself with the File | Compact MDB command?
8. Can you use Visdata to modify a table's structure once data has been entered?
9. Can you save queries in Visdata?
10. In what formats can you export data using the Visdata tool?
11. How would you use Visdata to convert an existing Access 2.0 database into
an
Access 7.0 format?
Exercises
You have been asked to build a database to track entities that purchase from and
sell to your organization. Complete the following tasks using Visdata as your development
tool.
- 1. Build a new database and name it Contacts. This database should have
a format that can be read by Microsoft Access 7.0.
2. Build a table of customers (tblCustomers). Include the following fields:
| Field |
Type |
Size |
| ID |
Text |
10 |
| Name |
Text |
50 |
| Address1 |
Text |
50 |
| Address2 |
Text |
50 |
| City |
Text |
50 |
| StateProv |
Text |
25 |
| Zip |
Text |
10 |
| Phone |
Text |
14 |
| Fax |
Text |
14 |
| Contact |
Text |
50 |
| Notes |
Memo |
NA |
-
- 3. Build a primary key (PKtblCustomers) on the ID field for the tblCustomers
table.
4. Print the table structure for tblCustomers.
5. Create and enter five sample records into the tblCustomers table.
6. Because you also need to track those from whom you purchase, copy the structure
(no records) from tblCustomers to a new table, tblVendors.
7. Export the data in the tblCustomers table to a text file.
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