Connecting to Databases - Overview

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Most dataset components can connect directly to a database server. Once connected, the dataset communicates with the server automatically. When you open the dataset, it populates itself with data from the server, and when you post records, they are sent back to the server and applied. A single connection component can be shared by multiple datasets, or each dataset can use its own connection.

Each type of dataset connects to the database server using its own type of connection component, which is designed to work with a single data access mechanism. The following table lists these data access mechanisms and the associated connection components:

Database connection components :

Data Access Mechanism	Connection Component
FireDAC	FireDAC.Comp.Client.TFDConnection
dbExpress	Data.SqlExpr.TSQLConnection
ActiveX Data Objects (ADO)	Data.Win.ADODB.TADOConnection
InterBase Express	IBX.IBDatabase.TIBDatabase
Borland Database Engine (BDE)	Bde.DBTables.TDatabase

Warning: The Borland Database Engine (BDE) has been deprecated, so BDE will not be enhanced. For instance, BDE will never have Unicode support. You should not undertake new development with BDE. Consider migrating your existing database applications from BDE to FireDAC. We provide a migration tool called reFind to help you in the migration process.

Note: For a discussion of some pros and cons of each of these mechanisms, see Using Databases.

The connection component provides all the information necessary to establish a database connection. This information is different for each type of connection component:

• For information about describing a FireDAC connection, see Setting up FireDAC Connection
• For information about describing a dbExpress connection, see Setting Up TSQLConnection.
• For information about describing an ADO-based connection, see Connecting to a Data Store Using TADOConnection.
• For information about describing an InterBase Express connection, see IBX.IBDatabase.TIBDatabase.
• For information about describing a BDE-based connection, see Identifying the Database.

Although each type of dataset uses a different connection component, they are all descendants of Data.DB.TCustomConnection. They all perform many of the same tasks and surface many of the same properties, methods, and events.

The following topics discuss many of these common tasks:

• Using Implicit Connections
• Controlling Connections
• Controlling Server Login
• Managing Transactions
• Working with Associated Datasets
• Sending Commands to the Server
• Obtaining Metadata

See Also

• Designing Database Applications - Overview
• Understanding Datasets - Overview
• Using Data Controls
• Working with Field Components - Overview
• Creating and Using a Client Dataset
• Working with ADO Components
• Using dbExpress Datasets
• Using the Borland Database Engine
• Using Provider Components
• Creating Multi-tiered Applications - Overview
• Using XML in Database Applications