Codeless
Database
Programming
I
n this c hapter, I’m go ing to sho w yo u ho w to c reate a wo rk-ing Visual Basic database pro gram witho ut writrk-ing a srk-ingle line o f c o de. I’ll use the ADO Data Co ntro l and so me c o mmo n c o ntro ls fo und in nearly every Visual Basic Pro gram.Data Binding
One o f the mo st po werful c o nc epts in Visual Basic is the c o n-c ept o f data binding. By using data binding, yo u n-c an delegate many o f the details o f mo ving data between yo ur database and yo ur pro gram.
What is data binding?
Data bindingis a tec hnique that allo ws a data so urc e to be tied to a data c o nsumer. Then when the data values asso c i-ated with the data so urc e c hange, the updi-ated info rmatio n is reflec ted in the data c o nsumer. Likewise, data values that are updated in the data c o nsumer are passed bac k to the data so urc e fo r updating.
One data control doesn’t fit all:There are three different data controls, one for each object m odel (DAO, RDO, and ADO). The DAO control is sim ply know n as the Data Control, w hile the RDO data control is also know n as the Rem oteData con-trol. The ADO Data Control is also called the ADODC. You should pick the data control corresponding to the object m odel you w ish to use and if you don’t have a specific need to use the DAO or RDO object m odels, you should use the ADO Data Control to take advantage of the enhancem ents and features in the ADO object m odel.
The binding info rmatio n is handled by setting vario us pro perty values in the bo und c o ntro ls. Two pro perties in partic ular are very impo rtant when binding a c o ntro l to a data so urc e. The DataSourcepro perty identifies the name o f the data so urc e c o ntro l, while the DataFieldpro perty identifies whic h database field will supply the data fo r the bo und c o ntro l.
Then, when yo ur applic atio n begins, the data c o ntro l establishes a c o nnec tio n with the database server and eac h o f the bo und c o ntro ls establishes a c o nnec tio n with the data c o ntro l. Whenever the data c o ntro l mo ves to a new rec o rd, the info rmatio n in eac h o f the bo und c o ntro ls c an be updated auto matic ally. Likewise, whenever the user c hanges a value in a bo und c o ntro l, the info rmatio n is passed bac k to the data c o ntro l, whic h in turn will auto matic ally update the database when the user mo ves to a different rec o rd.
Connecting to the database
After binding the c o ntro ls the user will interac t with the data c o ntro l, whic h needs to be c o nnec ted to the database. Again, this is handled via a set o f pro perties. The key pro perty is the ConnectionStringpro perty, whic h ho lds the info rmatio n needed to c o nnec t to the database server. This is a Stringvalue that c o ntains fo ur main piec es o f info rmatio n. The name o f the database server and the name o f the data pro vider are used to c reate a vehic le that c an be used to link the pro gram to the database server. Then the user name and passwo rd are used to authentic ate the user and determine the user’s privileges in the database.
in the table available to the user. Also , by spec ifying a table name, yo u wo n’t run into any c o mplic atio ns with adding rec o rds to yo ur database.
See Chapter 4 for details about Selectstatem ents.
Intrinsic bound controls
Visual Basic inc ludes two main types o f c o ntro ls: intrinsicand Active X. Intrinsic c o n-tro ls are inc luded with the Visual Basic runtime library and are always available to the Visual Basic pro grammer. While these c o ntro ls are no t true COM o bjec ts, they are muc h mo re effic ient and the mo st frequently used. Many o f these c o ntro ls c an might think that the ComboBoxc o ntro l might also be heavily used, there is a mo re database-friendly Ac tiveX c o ntro l c alled the DataComboc o ntro l that yo u will find yo urself using in plac e o f the ComboBoxc o ntro l in mo st applic atio ns.
ActiveX bound controls
Unlike the intrinsic bo und c o ntro l, the Ac tiveX bo und c o ntro ls are true COM o bjec ts and are external to the Visual Basic runtime libraries. Also , unlike the intrinsic bo und c o ntro ls, the Ac tiveX c o ntro ls are mo re c o mplex and have the ability to wo rk with mo re than o ne database field at a time.
✦DataList ✦MaskEdit
✦DataCombo ✦MonthVie w
✦DataGrid ✦MSFle xGrid
✦Date Time Picke r ✦MSChart
✦Image Combo ✦RichTe xtBox
Of these c o ntro ls, pro bably the mo st useful are the DataCombo, the DateTimePicker, the MaskEdit,and the MonthViewc o ntro l. All o f these c o ntro ls have o ne c o mmo n feature: they make it harder fo r a user to enter an inc o rrec t value into the pro gram.
Keep the Garbage Out
You’re probably fam iliar w ith the old expression “Garbage in, garbage out”. One of the m ost im portant goals of a database program m er is to prevent bad data from getting into the database. When you get bad data in your database, you m ay find it hard to isolate and cor-rect. I rem em ber a situation w here one slightly corrupted field in a database prevented a financial application from closing the books at the end of a fiscal year. It took nearly a w eek to track dow n and correct the bad piece of data. In the m eantim e, none of the other pro-gram s in the application w ould run correctly, and other processing involving the general ledger cam e to a com plete halt. In a sm all business this m ay not be a big problem , but in a billion dollar a year organization, you can believe the top-level m anagem ent w asn’t very happy. So think about it this w ay, keeping bad data out of your database is a good w ay of keeping yourself happily em ployed.
Building the Codeless Program
Building a c o deless pro gram is an interesting exerc ise and o ne that is pro bably wo rth yo ur time, espec ially if yo u are relatively new to Visual Basic . Bo und c o ntro ls will make yo ur life muc h easier, espec ially in mo re c o mplex applic atio ns. They defi-nitely reduc e the amo unt o f c o de yo u have to write in yo ur applic atio n and anything that reduc es the amo unt o f c o de yo u have to write appeals to the lazy pro grammer in everyo ne. Fo r the rest o f this c hapter, I’m go ing to sho w yo u ho w to build a c o de-less pro gram that allo ws yo u to ac c ess the Custo mers table in the database I designed in Chapter 3.
It’s your turn: This program is available on the CD-ROM as \VB6DB\ Chapter07\NoCode\Project1.vbp. To run this program , sim ply create a Data Link File as described in Configuring the ADO Data Control below for your
ADODC1control that reflects your database server, database nam e, user nam e, and passw ord inform ation. Then run the program .
Preparing your project
When yo u start Visual Basic , yo u have a number o f different pro jec t templates yo u c an c ho o se fro m. These templates allo w yo u to build many different types o f Visual Basic pro grams. Fo r this pro gram, I’m go ing to take the Standard EXE pro jec t and add everything I need to build the pro gram ( see Figure 7-1) .
The next step is to add the ADO Data Co ntro l to the pro jec t. This is do ne using the Co mpo nents dialo g bo x. To o pen this dialo g bo x, c ho o se Pro jec t➪Co mpo nents fro m the main menu. Then selec t the Co ntro ls tab if it isn’t already selec ted and sc ro ll do wn the list o f c o ntro ls until yo u find the Mic ro so ft ADO Data Co ntro l ( see Figure 7-2) . Clic k o n the c hec kbo x and press OK to add the c o ntro l to yo ur To o lbo x. On the
Figure 7-1: Selecting a Standard EXE project
The service pack game: Figure 7-2 reflects the nam es of the controls that w ere updated using Visual Studio Service Pack 3. This is identified by (SP3) in the nam e of the control.
Figure 7-2: Adding the ADO Data Control to the project
Configuring the ADO Data Control
Onc e yo u add the ADO Data Co ntro l to yo ur pro jec t, yo u need to plac e a c o py o f the data c o ntro l o n yo ur fo rm and set the pro perties so that it will ac c ess yo ur database. Yo u c an either set the pro perties tho ugh the Visual Basic Pro perties Windo w, o r yo u c an right c lic k o n the c o ntro l and selec t ADODC Pro perties fro m the po pup menu. This will display a set o f Pro perty Pages fo r the c o ntro l ( see Figure 7-3) .
Figure 7-3: Setting the data control’s properties
On the General tab , yo u’ll see that there are three different ways to c o nnec t to a datab ase server. Yo u c an use a Data Link File, an ODBC Data So urc e Name, o r a Co nnec tio n string. I’m go ing to sho w yo u ho w to b uild a Data Link File in this c hapter and yo u c an see ho w to c reate a Co nnec tio n String in Chapter 9.
OLE DB, not ODBC:The ADO Data Control is based on the OLE DB architecture, w hich is m ore efficient and offers a m ore flexible architecture. While you can cre-ate an ODBC Data Source, you w ould be m uch better off using a Data Link File or creating a Connection string.
Selecting a Data Link File
After selec ting Use Data Link File as the So urc e o f Co nnec tio n, press the Bro wse but-to n but-to either selec t an existing Data Link File o r c reate a new o ne. The Selec t Data Link File dialo g bo x (see Figure 7-4) will be displayed with the default direc to ry fo r data link files (\Program Files\Common Files\System\OLE DB\Data Links\). If yo u have an existing Data Link File, simply selec t it and press Open. If no t, yo u c an c reate o ne by right c lic king in the file area o f the dialo g bo x and c ho o sing New➪ Mic ro so ft Data Link. A new file c alled New Mic ro so ft Data Link will be c reated.
Figure 7-4: Choosing a Data Link File
Name of the game: I like to include the database server and the default database nam e in the nam e of m y Data Link files. This m akes it easy to identify the connec-tion inform aconnec-tion.
Choosing an OLE DB provider
Yo u c an edit the pro perties in a Data Link File by right c lic king o n its ic o n and selec ting Pro perties fro m the po pup menu. This will display the Pro perties dialo g bo x fo r the data link file. Selec t the Pro vider tab o f the Pro perties dialo g bo x to begin c o nfiguring yo ur data link ( see Figure 7-5) .
Figure 7-5: View ing the properties of a Data Link File
Define me before you use me: If you just created this file, you m ust edit the properties before it can be used.
There are a number o f c ho ic es fo r the data pro vider. Fo r best perfo rmanc e, yo u sho uld always c ho o se the OLE DB pro vider fo r yo ur database system. If yo u c an’t lo c ate o ne fo r yo ur spec ific database management system, then c ho o se Mic ro so ft OLE DB Pro vider fo r ODBC Drivers. Onc e yo u’ve c ho sen yo ur pro vider, press the Next butto n.
It isn’t there: Microsoft only supplies OLE DB providers for SQL Server and Oracle. If you are using a different database system , contact your database vendor to get their OLE DB provider.
Entering provider-specific information
Eac h OLE DB pro vider has a list o f info rmatio n it needs in o rder to c o nnec t to a database server. Figure 7-6 sho ws the info rmatio n required fo r the Mic ro so ft OLE DB Pro vider fo r SQL Server.
Figure 7-6: Selecting the database server and default database
There are three basic piec es o f info rmatio n needed in this fo rm: the name o f the database server, lo gin info rmatio n, and the name o f the default database. In this example, I’m using Athenaas my database server, Windo ws NT Authentic atio n fo r my lo gin info rmatio n and VB6DBas the default database.
Testing the connection
Onc e yo u’ve finished entering the pro perties, press the Test Co nnec tio n butto n to verify that yo u c an c o nnec t to the database server. If the info rmatio n yo u spec ify is c o rrec t, yo u sho uld see a message bo x saying, “Test c o nnec tio n suc c eeded”. If there is a pro blem, yo u will see an erro r message desc ribing the pro blem. Yo u sho uld then c o rrec t the info rmatio n yo u pro vided and try it again.
Choosing a RecordSource
The last step o f c o nfiguring the data c o ntro l is to c ho o se a so urc e o f data. This info rmatio n is sto red in the RecordSourcepro perty. Yo u c an edit this pro perty o n the Rec o rdSo urc e tab o f the Pro perties windo w. In this c ase, sinc e yo u want to make the Custo mers available via this pro gram, yo u sho uld c ho o se a CommandType
o f adCmdTableand then selec t the Custo mers table fro m the dro p-do wn list fo und immediately belo w that field ( see Figure 7-7) . This will auto matic ally be entered into the RecordSourcepro perty. Then I c an press OK to c lo se the Pro perty Pages dia-lo g bo x and save these values in the data c o ntro l.
Figure 7-7: Selecting the Custom ers table as the RecordSource
Adding bound controls
After adding and c o nfiguring the ADO Data Co ntro l, it’s time to add so me bo und c o ntro ls. I’m go ing to start by adding a text bo x fo r the Name field and binding it to the data c o ntro l ( see Figure 7-8) .
Drag a text bo x o nto yo ur fo rm, and size it to ho ld a perso n’s full name. Then view the Pro perties windo w and sc ro ll it so that the DataSourceand DataFieldpro perties are bo th visible. Selec t the DataSourcepro perty. A dro p-do wn arro w will appear at the end o f the pro perty’s value field. Press it and selec t the data c o ntro l fro m the dro p-do wn list. It sho uld be the o nly item o n the list.
Figure 7-8: Adding the text box for the Nam e field to your form
The Database Connection: You m ay not have given this m uch thought at this point, but the Visual Basic developm ent environm ent autom atically uses the con-nection inform ation you specified in the ADO Data Control to gather inform ation about your database at developm ent tim e. It then uses this inform ation to help you avoid m istakes w hen you enter values into the various properties. Of course, you can enter all of the inform ation for the bound controls m anually and then con-figure the data control, but that isn’t the lazy program m er’s w ay of doing things.
Testing your program
Even tho ugh this pro gram c an o nly display the perso n’s name fro m the Custo mers table, it is wo rth running it to verify that the pro gram ac tually wo rks. After c ho o s-ing Run➪Start fro m the main menu, the pro gram will lo ad, establish a c o nnec tio n to the database, retrieve the first ro w fro m the Custo mers table, and display the value fro m the Name field in the text bo x ( see Figure 7-9) .
Yo u c an press the Next Ro w butto n o n the data c o ntro l to display the name fro m the sec o nd ro w in the table and yo u c an return to the first ro w by pressing the Previo us Ro w butto n. Pressing the Last Ro w butto n will take yo u to the last ro w o f the table, while pressing the First Ro w butto n will return yo u to the first ro w in the table.
Finishing your program
Of c o urse, a pro gram that lists o ne field fro m a database table is a signific ant ac c o mplishment in terms o f all the little steps nec essary to make it wo rk, but it isn’t a terribly useful pro gram. So at this po int, yo u need to add c o ntro ls fo r the rest o f the fields in the table. Also , yo u sho uld take the time to plac e labels beside eac h field so that the user will understand the info rmatio n displayed. When yo u’ve fin-ished, yo ur fo rm might lo o k like the o ne sho wn in Figure 7-10.
Figure 7-9: Running your codeless program for the first tim e
Figure 7-10: Finishing your codeless program
Updating database information
To c hange a value in the database using this pro gram, simply c hange the value in the field and mo ve to ano ther ro w. As yo u c hange the data displayed o n the fo rm, the bo und c o ntro ls pass the c hanges bac k to the data c o ntro l, whic h will auto mati-c ally update the ro w when it mo ves to ano ther ro w. Of mati-c o urse, if there is an erro r
Previous row First row
with the update pro c ess, a message bo x will appear and yo u will remain o n the c ur-rent ro w until yo u c o rrec t the pro blem.
Using numeric fields
Yo u may rememb er that the Zip field sto res its info rmatio n using a 32-b it integer rather than a c harac ter string. While yo u might think that so me spec ial c o de might b e nec essary to handle the data c o nversio n fro m Longto Stringand b ac k again, yo u wo uld b e wro ng. The c o nversio n is handled auto matic ally b y the text b o x c o ntro l.
One limitatio n o f using text bo xes to display numeric info rmatio n is that yo u c an enter no n-numeric info rmatio n into the text bo x witho ut immediately triggering an erro r. Of c o urse, attempting to update the ro w will trigger a runtime erro r bec ause yo u c an’t put a no n-numeric value into a numeric field.
Using Boolean fields
Booleanfields are a natural fit fo r the CheckBoxc o ntro l. Yo u set the DataSource
and DataFieldpro perties just like the TextBoxc o ntro l. The c o ntro l will display a
TRUEvalue by plac ing a c hec k mark in the c hec k bo x and will c lear the c hec k bo x when the database value is FALSE.
Using Datetime fields
Like numeric values, date and time values also undergo a dynamic c o nversio n pro -c ess when info rmatio n is displayed in the -c o ntro l. As lo ng as the date and time info rmatio n is pro perly fo rmatted and legal, the c o ntro l will auto matic ally handle the c o nversio n. If there is an erro r, the o ld Operatio n c anc eled message will be dis-played, and the o riginal values will be resto red.
Adding new records
By default, the ADO Data Co ntro l do esn’t allo w yo u to add new rec o rds to the database. Ho wever, by c hanging o ne pro perty value, yo u c an easily inc lude this c apability in yo ur c o deless pro gram. The EOFActionpro perty determines what happens when the user attempts to mo ve beyo nd the last ro w in the table.
By default, the data c o ntro l will simply mo ve the user bac k to the last ro w in the table if the user attempts to mo ve beyo nd it. Ho wever, if yo u set EOFActionto
adDoAddNew( 2) , the data c o ntro l will auto matic ally add a new blank ro w anytime the user attempts to mo ve beyo nd the end o f the file.
I’ve added a record and I can’t get out: One dow nside to using a codeless pro-gram to add records to your database is that there isn’t a convenient m ethod to abort the add process. In fact, the only w ay to abort the add process is to end the program , w hich is pretty drastic. Of course, this is a situation w here a little code can go a long w ay tow ards m aking the program m uch easier to use.
Summary
In this c hapter yo u learned the fo llo wing:
✦What data binding is and ho w it wo rks.
✦Whic h c o ntro ls yo u c an bind in yo ur Visual Basic pro gram.
✦Ho w yo u c an use bo und c o ntro ls to build a meaningful pro gram witho ut any c o de.
✦Ho w to c ho o se an OLE DB pro vider and build an ADO c o nnec tio n string to c o nnec t to yo ur database.
✦
✦
✦
Caution
Thoughts on Codeless Programming
Okay, so a codeless program m ay not be perfect, but it w ill w ork and can often be useful in the early stages of building an application. If you’re w illing to add a little code to handle non-database functions, such as edit checking and m enu m anagem ent, Visual Basic offers a m uch better alternative to building a database application in Access.
Access is prim arily an easy to use database form s generator w ith som e scripting capabilities added. While it allow s you to build sim ple database applications quickly, w hen building m ore com plex applications you constantly run into situations that aren’t easy to handle because of the m any lim itations in Access. How ever, Visual Basic is a true program m ing lan-guage and doesn’t suffer from the sam e lim itations.
