Delphi - Database Application Developers Book.pdf - delphi - JoePapa

Database Application

Delphi for Windows

Chapter 1

Introduction

Agreement

Delphi enables you to create robust database applications quickly and easily. Delphi

database applications can work directly with desktop databases like Paradox, dBASE,

the Local InterBase Server, and ODBC data sources. The Delphi Client/Server edition

also works with remote database servers such as Oracle, Sybase, Microsoft SQL Server,

Informix, InterBase, and ODBC data sources. Delphi client applications can be scaled

easily between mission critical network-based client/server databases, and local

databases on a single machine.

This chapter introduces Delphi’s database tools, including the Data Access and Data

Controls component pages, the Fields Editor, the Database Desktop, and the Database

Forms Expert.

What you should know first

Building a database application is similar to building any other Delphi application. This

book assumes you understand the basic application development techniques covered in

the Delphi User’s Guide , including:

• Creating and managing projects

• Creating forms and managing units

• Working with components , properties, and events

• Writing simple Object Pascal source code

You also need to have a working knowledge of the Database Management System

(DBMS) your Delphi database applications access, whether it is a desktop database such

as dBASE or Paradox, or an SQL server. For information specific to building

client/server applications with Delphi, see Chapter 6, “Building a client/server

application.”

This book assumes you have a basic understanding of relational databases, database

design, and data management. There are many third-party books covering these topics

if you need to learn more about them.

Introduction 1

Developer’s Guide

Overview of Delphi’s database features and capabilities

A Delphi database application is built using Delphi database development tools, Delphi

data-access components, and data-aware GUI components. A database application uses

Delphi components to communicate with the Borland Database Engine (BDE), which in

turn communicates with databases. The following figure illustrates the relationship of

Delphi tools and Delphi database applications to the BDE and data sources:

Figure 1.1 Delphi database architecture

Delphi IDE

ReportSmith

Delphi Appli cation

Database

Desktop (DBD)

BDE

Configuration

Utility

Report

Borland Database Engine (BDE)/IDAPI

SQL Links

ODBC Drivers

ReportSmith Drivers

dBASE

Paradox

ASCII

TCP/IP, SPX/IPX, etc.

InterBase

for Windows

Remote Data Sources

Oracle

Sybase

Informix

InterBase

Local Data Sources

. . .

The following table summarizes Delphi’s database features.

Table 1.1

Database features summary

Tool

Purpose

Data Access components

Access databases, tables, stored procedures, and custom component

editors.

Data Control components

Provide user interface to database tables.

Database Desktop (DBD)

Create, index, and query Paradox and dBASE tables, and SQL

databases. Access and edit data from all sources.

2 Database Application Developer’s Guide

Table 1.1

Database features summary (continued)

Tool

Purpose

ReportSmith

Create, view, and print reports.

Borland Database Engine (BDE)

Access data from file-based Paradox and dBASE tables, and from

local InterBase server databases.

BDE Configuration Utility

Create and manage database connection Aliases used by the BDE.

Local InterBase Server

Provides a single-user, multi-instance desktop SQL server for

building and testing Delphi applications, before scaling them up to a

production database, such as Oracle, Sybase, Informix, or InterBase

on a remote server.

InterBase SQL Link

Native driver that connect Delphi applications to the Local InterBase

Server.

These features enable you to build database applications with live connections to

Paradox and dBASE tables, and the Local InterBase Server through the BDE. In many

cases, you can create simple data access applications with these components and their

properties without writing a line of code.

The BDE is built into Delphi components so you can create database applications

without needing to know anything about the BDE. The Delphi installation program

installs drivers and sets up configuration for Paradox, dBASE, and the Local InterBase

Server, so you can begin working with tables native to these systems immediately. The

BDE Configuration Utility enables you to tailor database connections and manage

database aliases.

Advanced BDE features are available to programmers who need more functionality.

These features include local SQL, which is a subset of the industry-standard SQL that

enables you to issue SQL statements against Paradox and dBASE tables; low-level API

function calls for direct engine access; and ODBC support for communication with other

ODBC-compliant databases, such as Access and Btrieve.

Delphi includes Borland ReportSmith, so you can embed database report creation,

viewing, and printing capabilities in Delphi database applications. Delphi also includes

the Database Desktop (DBD), a tool that enables you to create, index, and query desktop

and SQL databases, and to copy data from one source to another. For more information

about ReportSmith, see Creating Reports . For more information about the DBD, see

Appendix A, “Using Database Desktop.”

The Local InterBase Server is a single-user, multi-instance, 16-bit, ANSI SQL-compliant,

Windows-based version of Borland’s 32-bit InterBase SQL server that is available for

Novell NetWare, Windows NT, and Unix. For more information, see the Local InterBase

Server User’s Guide .

The following table lists the additional database features available in the Client/server

edition of Delphi. These features extend Delphi’s database capabilities to access remote

Introduction 3

SQL database servers such as Sybase, Microsoft SQL Server, Oracle, Informix, and

InterBase.

Table 1.2 Additional Delphi Client/Server database features

Tool Purpose

SQL Drivers Both SQL Links and ReportSmith provide native drivers that connect Delphi

database applications to remote SQL database servers, such as Oracle, Sybase,

Microsoft SQL Server, Informix, and InterBase.

Visual Query Builder Creates SQL statements by visually manipulating tables and columns.

SQL Links provide Delphi applications with SQL access to data residing on remote

servers, including Sybase, Microsoft SQL Server, Oracle, and Informix. When an SQL

Link driver is installed, SQL statements are passed directly to the server for parsing and

execution. For more information about using passthrough SQL, see Chapter 5, “Using

SQL in applications.”

What is a database?

Delphi programmers should understand some basic concepts about databases, data,

and data access, before building database applications. A database consists of one or

more tables, where each table contains a series of columns into which records (also

called “rows”) are stored. Each record is identical in structure. For example, a database

of addresses consists of a table with name, street address, city, state, and zipcode

columns. The intersection of a single column and row is referred to as a field. Fields

contain values. The following figure illustrates these concepts:

Figure 1.2 Structure of a table

Column names

CustNo Name

Street

City

Current field

1221

1231

Kauai Dive Shoppe

Unisco

4-976 Sugarloaf Highway

PO Box Z-547

Kapaa Kauai

Freeport

Current record

1251

Sight Diver

1 Neptune Lane

Kato Paphos

Records

1254

Cayman Divers Wo

PO Box 541

The current field is one field in a single record. The current record is a single record in a

multi-record set that is the focus of attention. For example, some Delphi database

applications display multiple columns and records in a grid format for editing. As far as

Delphi controls are concerned, only one field in a single record is “current,” meaning

that editing tasks affect only the data in that field.

Different databases vary widely in structure. A database in Paradox consists of one or

more files, each of which contains a single table or index, but an SQL relational database

on a remote server generally consists of a single file that contains all tables, indices, and

4 Database Application Developer’s Guide

other database structures. Delphi’s Data Access and Data Control components

encapsulate the underlying structure of the databases your application uses, so that

your application can present the same interface to an end user whether it accesses a local

Paradox file or a database on a remote SQL server.

The information in most databases is constantly changing. When you access a

networked database from a Delphi application, many users may be accessing and

updating the database at the same time. When any database application accesses a

database, whether to process a query or generate a report, the application receives a

snapshot of the database as it was at the time the application accessed the database. An

application’s view of data may differ from the data currently in the database, so

database applications should always be robust enough to react to such data changes. For

more information about building client/server applications that access remote data, see

Chapter 6, “Building a client/server application.”

What is data?

In this book, “data” refers to information stored in a database. Data may be a single item

in a field, a record that consists of a series of fields, or a set of records. Delphi

applications can retrieve, add, modify, or delete data in a database.

What is data access?

Delphi applications can access data from desktop database tables on a file server or local

disk drive and from remote database servers. To access a data source, a Delphi

application uses Data Access components to establish a connection through the BDE.

The installation program for Delphi installs drivers and sets up configurations for

Paradox, dBASE, and the Local InterBase Server so you can begin working with tables

native to these systems immediately.

To connect to another data source requires the installation of a driver for that specific

database and subsequent configuration of the BDE to recognize the driver. Connecting

to remote database servers requires the Client/Server edition of Delphi that includes

SQL Links to access to Sybase, Microsoft SQL Server, Oracle, Informix, and InterBase on

NT, NetWare, and Unix servers. For more information about installing and configuring

the SQL Link drivers, see the SQL Links User’s Guide .

The BDE uses aliases as convenient shorthand names for often-used data sources,

whether local or remote. The BDE Configuration Utility enables you to define and

modify aliases that Delphi applications can use immediately. For more information

about defining aliases, see Appendix B, “Using the BDE configuration utility.”

Once drivers are installed and network connections established, Delphi applications can

access data from any authorized server. The examples in Chapter 2 demonstrate

techniques for accessing data from a database—specifically, sample data tables that are

shipped and installed as part of the Delphi package. Although the example project in

the next chapter deals with local desktop data, the techniques for accessing remote data

are essentially the same, as subsequent chapters demonstrate.

Note An SQL version of the example project is provided in the DEMOS directory.

Introduction 5

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