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Slide 33 -
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Developing Win32 Database Applications with Delphi Cary 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 Delphi C++
Builder Data
Gateway Visual
dBASE Borland Database Engine (BDE) Local Tables
Paradox, dBASE,
Access, FoxPro Remote Tables
Oracle, Sybase,
MS SQL Server, ... ODBC-ready
databases 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.DLL
if MidasLib unit not used Local File XML 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 Connection
Component Remote Data Module
with 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
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