RAD Studio |  |

Connecting to databases
Collapse All
Topics

Name | Description
Controlling Connections | Before you can establish a connection to a database server, your application must provide certain key pieces of information that describe the desired server. Each type of connection component surfaces a different set of properties to let you identify the server. In general, however, they all provide a way for you to name the server you want and supply a set of connection parameters that control how the connection is formed. Connection parameters vary from server to server. They can include information such as user name and password, the maximum size of BLOB fields, SQL roles, and so on. Once... more
Disconnecting from a Database Server | There are two ways to disconnect a server using a connection component: Set the Connected property to False. Call the Close method. Calling Close sets Connected to False. When Connected is set to False, the connection component generates a BeforeDisconnect event, where you can perform any cleanup before the connection closes. For example, you can use this event to cache information about all open datasets before they are closed. After the BeforeConnect event, the connection component closes all open datasets and disconnects from the server. Finally, the connection component generates an AfterDisconnect event, where you can respond... more
Managing Transactions | A transaction is a group of actions that must all be carried out successfully on one or more tables in a database before they are committed (made permanent). If one of the actions in the group fails, then all actions are rolled back (undone). By using transactions, you ensure that the database is not left in an inconsistent state when a problem occurs completing one of the actions that make up the transaction. For example, in a banking application, transferring funds from one account to another is an operation you would want to protect with a transaction. If, after decrementing... more
Obtaining Metadata | All database connection components can retrieve lists of metadata on the database server, although they vary in the types of metadata they retrieve. The methods that retrieve metadata fill a string list with the names of various entities available on the server. You can then use this information, for example, to let your users dynamically select a table at runtime. You can use a TADOConnection component to retrieve metadata about the tables and stored procedures available on the ADO data store. You can then use this information, for example, to let your users dynamically select a table or stored procedure... more
Sending Commands to the Server | All database connection components except TIBDatabase let you execute SQL statements on the associated server by calling the Execute method. Although Execute can return a cursor when the statement is a SELECT statement, this use is not recommended. The preferred method for executing statements that return data is to use a dataset. The Execute method is very convenient for executing simple SQL statements that do not return any records. Such statements include Data Definition Language (DDL) statements, which operate on or create a database's metadata, such as CREATE INDEX, ALTER TABLE, and DROP DOMAIN. Some Data Manipulation Language (DML) SQL... more
Specifying the Transaction Isolation Level | Transaction isolation level determines how a transaction interacts with other simultaneous transactions when they work with the same tables. In particular, it affects how much a transaction "sees" of other transactions' changes to a table. Each server type supports a different set of possible transaction isolation levels. There are three possible transaction isolation levels: DirtyRead: When the isolation level is DirtyRead, your transaction sees all changes made by other transactions, even if they have not been committed. Uncommitted changes are not permanent, and might be rolled back at any time. This value provides the least isolation, and is... more
Using Implicit Connections | No matter what data access mechanism you are using, you can always create the connection component explicitly and use it to manage the connection to and communication with a database server. For BDE-enabled and ADO-based datasets, you also have the option of describing the database connection through properties of the dataset and letting the dataset generate an implicit connection. For BDE-enabled datasets, you specify an implicit connection using the DatabaseName property. For ADO-based datasets, you use the ConnectionString property. When using an implicit connection, you do not need to explicitly create a connection component. This can simplify your application development,... more
Working with Associated Datasets | All database connection components maintain a list of all datasets that use them to connect to a database. A connection component uses this list, for example, to close all of the datasets when it closes the database connection. You can use this list as well, to perform actions on all the datasets that use a specific connection component to connect to a particular database.
Connecting to Databases: Overview | 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 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... more
Controlling Server Login | Most remote database servers include security features to prohibit unauthorized access. Usually, the server requires a user name and password login before permitting database access. At design time, if a server requires a login, a standard login dialog box prompts for a user name and password when you first attempt to connect to the database. At runtime, there are three ways you can handle a server's request for a login: The first way is to let the default login dialog and processes handle the login. This is the default approach. Set the LoginPrompt property of the connection component to True... more
Connecting to a Database Server | There are two ways to connect to a database server using a connection component: Call the Open method. Set the Connected property to True. Calling the Open method sets Connected to True. Note: When a connection component is not connected to a server and an application attempts to open one of its associated datasets, the dataset automatically calls the connection component's Open method. When you set Connected to True, the connection component first generates a BeforeConnect event, where you can perform any initialization. For example, you can use this event to alter connection parameters. After the BeforeConnect... more

Copyright(C) 2009 Embarcadero Technologies, Inc. All Rights Reserved.
What do you think about this topic? Send feedback!