Copyright © 2001 by Wiley. All rights reserved. Chapter 9: Introduction to Working with Databases...

Introduction to Programming with Visual Basic 6.0 by McKeown and Piercy

1Copyright © 2001 by Wiley. All rights reserved.

Chapter 9: Introduction to Working with Databases in Visual Basic

Database Concepts

Relational Database

The Data Control

The Recordset Object

Finding Records





Database Concepts

Relational Database

The Data Control


Finding Records

Database Concepts• Database: the storage of different types of data in

such a way that the data can be easily manipulated and retrieved by an end user. A database is composed of fields, records, and tables.

• Field: a single fact or data. It is the smallest use of named data that has meaning in a database. Fields are given field names to identify them.

• Record: A collection of related data that is treated as a unit. A collection of fields that pertain to a single person, place or thing.

• Table: A related collection of records, all having the same fields. Composed of rows and columns.




Database Concepts

Relational Database

The Data Control


Finding Records

A Database Table




Database Concepts

Relational Database

The Data Control


Finding Records

Relational Database• A relational database is composed of multiple

related tables. It is the most common form of database in use today.

• A primary key is a field that has a unique value for each record in a table.

• A foreign key is a field that is a primary key in another table.

• Foreign keys are used to establish the relationships between the various tables in the database.




Database Concepts

Relational Database

The Data Control


Finding Records

Relational Database




Database Concepts

Relational Database

The Data Control


Finding Records

Database Operations• The primary use of a database is to enable

the user to obtain information from it by constructing queries to it.

• For a relational database, these queries are constructed using SQL (Structured Queried Language).

• Once found, records can be displayed, edited, deleted, or added.




Database Concepts

Relational Database

The Data Control


Finding Records

Advantages of Databases vs. Arrays

• Databases are superior to arrays for the following reasons:– A database table can store multiple types of

data in the same table while arrays are restricted to a single data type.

– Any changes to the database are immediately saved to disk as they occur.

– A sophisticated database engine can be used to handle processing.

– Multiple computers can be connected to the same database.




Database Concepts

Relational Database

The Data Control


Finding Records

Using VB to Work with Databases

• Visual Basic can be used to work with existing databases.

• In our case, we will assume a Microsoft Access database with an .mdb extension.

• Visual Basic can be used to create a user-friendly front-end to a database.

• The data control (with dat prefix) is essential to working with databases in VB.

• It uses an internal pointer to point to the current record.




Database Concepts

Relational Database

The Data Control


Finding Records

The Data Control• DatabaseName property must be set to the

pathname of the database.• RecordSource property must be set to the table of

the database.• Textboxes and other controls can be bound to a

data control by assigning their DataSource property to the data control.

• The bound control’s DataField property is set to a field of the DataSource table.

• The Recordset object represents the records in the database.




Database Concepts

Relational Database

The Data Control


Finding Records

RecordSet Methods

• There are numerous useful methods for the Recordset object:– MoveFirst - move to first record– MoveLast - move to last record– MoveNext - move to next record– MovePrevious - move to previous record– AddNew - add a new record (save by moving

to new record or using UpdateRecord method)– Delete - delete current record– UpdateControls - make bound controls the

same as database




Database Concepts

Relational Database

The Data Control


Finding Records

Recordset Properties• There are numerous useful properties for the

Recordset object:

– AbsolutePosition - the current position of pointer

– RecordCount - the number of records in the Recordset

– BOF (EOF) - True if at Beginning (End) of File– Bookmark - A unique identification of each

record




Database Concepts

Relational Database

The Data Control


Finding Records

Finding Records• The form of the FindFirst method to find first

occurrence of a matching record is:datName.Recordset.FindFirst Query string

where the Query string is in quotation marks and is a combination of field name, comparison operator, and a value. For example:

datMembers.Recordset.FindFirst “Late_Fees > 0”

• If the NoMatch property is true, no record matches the query.

• An Until NoMatch loop can be used with the FindNext method to find all matches.




Database Concepts

Relational Database

The Data Control


Finding Records

The Field Property and More on Query Strings

• To find the value of a field of the current record, use the RecordSet Field property, e.g., datMembers.Recordset(“Name”)

• A query string can be the combination of the field name and the comparison operator with some value--this enables variable query strings

• Strings in query strings must be enclosed in apostrophes, e.g.,

“Phone Number = “ & “’” & PhoneNum & “’”

Copyright © 2001 by Wiley. All rights reserved. Chapter 9: Introduction to Working with Databases...

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