Visual Basic 6 Black Book:Databases: Using DAO, RDO, And ADO
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Chapter 24Databases: Using DAO, RDO, And ADO


If you need an immediate solution to:
Creating And Managing Databases With The Visual Data Manager
Creating A Table With The Visual Data Manager
Creating A Field With The Visual Data Manager
Entering Data In A Database With The Visual Data Manager
Adding A Data Control To A Program
Opening A Database With The Data Control
Connecting A Data Control To A Bound Control
Registering An ODBC Source
Opening A Database With A Remote Data Control
Connecting A Remote Data Control To A Bound Control
Opening A Database With An ADO Data Control
Connecting An ADO Data Control To A Bound Control
The Data Form Wizard: Creating A Data Form
Using Database Control Methods: Adding, Deleting, And Modifying Records
Adding Records To Databases
Deleting Records In Databases
Refreshing A Data Control
Updating A Database With Changes
Moving To The Next Record
Moving To The Previous Record
Moving To The First Record
Moving To The Last Record
The Data-Bound Controls: From Text Boxes To Flex Grids
The ADO Data-Bound Controls

In Depth
This is our first chapter on databases. In this chapter, we’re going to see what databases are, exploring the difference between the Microsoft database programming object sets: Data Access Objects (DAO), Remote Data Objects (RDO), and ActiveX Data Objects (ADO).

You may wonder why there are three different sets of database objects in Visual Basic. As it turns out, the reason is historical. At first, Visual Basic only supported DAO, which connected to the Microsoft Jet database engine (the database engine in Microsoft Access). Then, recognizing that there are other database types available, Microsoft created the open database connectivity (ODBC) standard and supported ODBC with Remote Data Objects in Visual Basic. Finally, Microsoft saw that the Web was available too and created Active Data Objects, which make up a flexible standard that allows connections on the same computer, over networks, and through the Web, and is intended to supercede ODBC. ADO is also called OLE DB, and in fact, it’s based on COM programming techniques (which we’ll see a lot more of in Chapter 26). We’ll see how to work with all three of these object sets in this and the next chapter.
There are two ways to work with the DAO, RDO, and ADO object sets in Visual Basic. The first way is working with the special controls that support them: the data control (supports DAO), the remote data control (supports ODBC), and the ADO data control (supports ADO). You use those controls to connect to and move through databases, but they don’t actually display data—you bind them to other Visual Basic controls, and those bound controls handle the display. The second way is working with the three database object sets directly in code, without controls like the data control or the ADO data control, and that’s what we’ll do in the next chapter.
In this chapter, then, we’ll see what databases are all about and how to create and edit them with the Visual Basic Visual Data Manager tool. Next, we’ll examine the data control, the remote data control, and the ADO data control to see how to connect to databases, and we’ll use the bound controls to handle those databases in depth. In the next chapter, we’ll see how to access the data object libraries directly and put them to work in code for additional power.
What Are Databases?
We’ll begin our discussion of databases by asking just what they are. Like many other programming concepts, databases have become more complex over the years, but the fundamental concept is still a simple one. Say you were in charge of teaching a class and were supposed to hand a grade in for each student. You might make up a table much like the one in Figure 24.1 to record the grade for each student.


Figure 24.1  A table of data.
In fact, you’ve already created a database—or more specifically, a database table. The transition from a table on paper to one in a computer is natural: with a computer, you can sort, index, update, and organize large tables of data in an easy way (and without a great waste of paper). You can even connect tables together, creating relational databases.
Each individual data entry in a table, such as a student’s name, goes into a field in the table. A collection of fields together, such as the Name and Grade fields in our table, make up a record. Each record gets its own row in a table, and each column in that row represents a different field.
A collection of records—that is, rows of records where each column is a field—becomes a table. What, then, is a database? A database is just a collection of one or more tables. In fact, you can go farther than that in Visual Basic—you can have collections of databases. In DAO, those collections are called the workspace, and in RDO and ADO, they are referred to as the data environment. You can also have indices in databases, and those are pointers to specific fields, either in the current database or another one.
Now that you’ve set up a database, how do you work with the data in that database? One popular way is to use Structured Query Language (SQL), which we’ll see more about in the next chapter. You use SQL to set up a query, which when applied to a database gives you a record set. This record set is made up of the records from the database that matched your query—for example, you may have asked for all students that got a grade of B or better. We’ll see more about working with databases in code like this in the next chapter.



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