Developing Win32 Database Applications with DelphiCary Jensen

Jensen Data Systems, Inc.

Overview

General Comments About Delphi’s Data Access Technologies

Overview of Data Access Technologies The Borland Database Engine dbExpress dbGo (ADO) MyBase InterBase Express DataSnap Third-Party Data Access Options

Data Modules Data Aware Controls Programming with Data Providers

TDataSet

The Origins Paradox, the Paradox Engine, ODAPI, IDAPI, IDAPI, BDE

The Legacy A navigational interface in a largely set-based world

Things changed with Delphi 3

DelphiC++

BuilderData

GatewayVisualdBASE

Borland Database Engine (BDE)

Local TablesParadox, dBASE,

Access, FoxPro

Remote TablesOracle, Sybase,

MS SQL Server, ...

ODBC-readydatabases

SQL Links

TCP/IP, SPX/IPX, NetBEUI ODBC Driver

ODBC Socket

Session (default)

Database (default)

DataSets (Table,Query, StoredProc)

DataSource

Data Controls (DBGRid, etc.)

BDE

BDE Advantages

If you already have it installed and working for existing applications, new applications require little or no configuration to use it

Many legacy applications exist which use it Two or more applications written in Delphi can easily

share global aliases It has relatively good performance across a large

number of data types It provides access to installed ODBC drivers

BDE Limitations

In the typically deployment of BDE-based applications, a copy of the BDE must be installed and configured on each workstation (a network installation is possible, but requires manual registry configuration)

The BDE is somewhat inefficient, in that it stores as many as three copies of table metadata

When used with local tables such as Paradox tables, failure to correctly configure the BDE can produce periodic index corruption

If a new BDE application is incorrectly installed, existing BDE applications may fail to initialize properly

The BDE is available only for the Windows platform

Vendor Library

Database

Delphi’s dbExpress

Components

dbExpress Driver

dbExpress

SQLConnection

DataSource

ClientDataSet

DataSetProvider

SQLClientDataSet

Unidirectional DataSets

Data Aware Controls

dbExpress

dbExpress Advantages

Data-related operations in dbExpress tend to be faster than using other technologies

dbExpress-based applications can be deployed under both Windows and Linux environments

Applications designed to use dbExpress can more easily be ported to using DataSnap

dbExpress applications require fewer support files and can require far less configuration than BDE applications

dbExpress Limitations

dbExpress applications are generally more complicated than other types of Delphi database applications to program. In addition to requiring more components to access and edit data, dbExpress applications often require more lines of code than non-dbExpress applications

There are relatively few dbExpress drivers available

ActiveX

OLE DB Provider

Data

Delphi ADO Datasets

Microsoft Universal Data Access (MDAC)

Data Access Components

Plugable Layer

Data (database,spreadsheet, document, etc.)

TDataSet Descendants

DataSource

Data Aware Controls

TADOCommand

TADOConnection

ActiveX Data Objects

ADO Advantages

All Windows-based computers shipped in the past few years already have MDAC installed. As a result, most ADO-based applications require only the installation of the specific OLE DB provider, at most

ADO can be used from a wide range of development environments, including MS Access, VisualBasic, Delphi, Visual C++, to name of few

A wide range of OLE DB providers are available Applications that have been deployed as COM+ applications (formerly

referred to Microsoft Transaction Server components), can pool ADO connections, producing improved performance in environments that require large numbers of independent requests for data, such as Web server extensions

ADO Limitations

ADO is available only for the 32-bit Windows operating system Having MDAC installed and configured is not enough. In some cases, you

must also install and register an appropriate OLE DB provider Performance using ADO is largely reliant on the quality of the OLE DB

provider that you are using If you are using the OLE DB provider for ODBC, an appropriate ODBC

driver must also be installed and configured

MIDAS.DLLif MidasLib unit not used

Local FileXML or CDS

ClientDataSet

MyBase - ClientDataSet

DataSource

ClientDataSet

Data Aware Controls

MyBase

MyBase Advantages

MyBase applications have minimal installation requirements

The data can be stored in XML format, making it easy to access this data from outside of the application

Data can be loaded and saved without code. Simply point the client dataset's FileName property to a file that contains the proper XML or binary client dataset data, and it will take care of the rest. (It is better to explicity load and save using SaveToFile and LoadFromFile)

MyBase Limitations

Because the records in a client dataset are stored in-memory, the number of records that you can load is limited by the amount of real and virtual memory available on your machine

Large files may take a significant amount of time to load from a file into a client dataset. For example, 100,000 records may take 5 seconds or so to load into memory

MyBase applications are limited to single user applications. If you want to create a multiuser application, you must use one of the other available technologies

gds32.dll

InterBase

IBDatabase

InterBase Express

IBTransaction

IBDatabase

IBTransaction

IBSQL

IBTable, IBQuery, IBStoredProc, IBDataSet

DataSource

Data Aware Controls

InterBase Express

InterBase Express Advantages

InterBase Express provides access to InterBase without the BDE

Because InterBase Express components are designed specifically for InterBase, they include a number of specialized components that access and leverage InterBase features

Interbase Express components are available for both Delphi and Kylix, meaning that you can build applications that employ InterBase Express for machines running Linux

InterBase Express Limitations

InterBase Express works only with the InterBase database server

Database Server

DataSnap Server

DataSnap Clients DataSnap

Data Access Components

Database

Remote ConnectionComponent

Remote Data Modulewith DataSetProviders

DataSource

ClientDataSet

Data Aware Controls

Connection Components

SharedConnection

DataSetProvider

LocalConnection

ConnectionBroker

DataSnap

DataSnap Advantages

DataSnap client applications have few installation requirements

Business rules can be implemented on a server, permitting these rules to be updated independent of the individual client applications

They permit load balancing They can implement fail-over for high reliability They provide a reliable, distributed upgrade path to

dbExpress and MyBase applications The connection components support a variety of

internetworking protocols

DataSnap Limitations

While DataSnap offers additional flexibility over traditional client/server solutions, it requires more development. Specifically, in addition to writing the client application, you also need to write the application server

DataSnap applications require an additional license before they can be deployed. However, since Delphi 6, this license comes with the Enterprise and Architect editions of Delphi

DataSnap servers must also employ one of the other data access mechanisms. For example, the application server may use the BDE or ADO. As a result, DataSnap application developers must be familiar with at least two data access mechanisms (DataSnap plus at least one more)

Third-Party Data Access Components

Third-Party Data Controls Advantages

May support specialized features of the vendor’s database If designed with the TDataSet interface in mind, it may be easy to convert

from some other data access mechanism to the vendor’s data access mechanism

Third-party vendors are generally highly motivated to provide nearly bug-free components

Third-Party Data Controls Limitations

Typically support only one database Ties you to that vendors database

Data Modules

Non-visual container for non-visual components Permit sharing of objects Excellent classes for implementing custom components Are not always appropriate for data controls, especially

in the following situations Multi-instance forms Forms used for reports Unique data views

Data Aware Controls

Convenient and effective Permit you to build interfaces quickly Automatically respond to changes in the data Some developers have a bias against data aware

controls In response, they often create their own framework of

data awareness with custom controls

Using Providers in Database Applications

Independent layer for data access Decouples your user interface from the data access

mechanism Is a more generalized approach than data modules

Thank You !

Thank You !