PostgreSQLDatabase

Description

Used to open a PostgreSQL database.

Super Class

Database

Events

Name	Parameters	Description
ReceivedNotification	Name as String, ID as Integer, Extra as String	A notification named Name has been received. The process ID of the sender is passed in the ID parameter. At the current time, the Extra parameter will always be empty although it may be implemented in the future.

Properties

Name	Type	Description
Port	Integer	The port of the PostgreSQL database to connect to. PostgreSQL's default port is 5432.

Methods

Name	Parameters	Return Type	Description
CheckForNotifications			Checks to see if there are any waiting notifications. You will receive notifications as a ReceivedNotification event. If you would like to receive notifications automatically, create a Timer and use it to call CheckForNotification repeatedly.
CreateLargeObject		Integer	Creates a PostgreSQLLargeObject and returns its ID. Legal IDs are positive integers. Therefore, if CreateLargeObject returns 0 or less, then there was an error creating the large object. Use ErrorMessage to determine what the error was.
DeleteLargeObject	ID as Integer		Deletes the large object denoted by the process ID, ID.
Listen	Name as String		Listens for notifications named "Name".
Notify	Name as String		Sends a notification named "Name".
OpenLargeObject	ID as Integer, [ReadOnly as Boolean]	PostgreSQLLargeObject	Opens the large object specified by the passed ID. The ReadOnly parameter is optional and defaults to False. If you pass True, then the large object will be opened in read-only mode. If OpenLargeObject is successful, it returns an instance of PostgreSQLLargeObject.
Unlisten	Name as String		Stops listening for notifications named "Name".

Notes

The PostgreSQLDatabase class requires the PostgreSQL Database plug-in. Place this plug-in in the REALbasic Plugins folder. The PostgreSQL Database plug-in ships with REALbasic and you can find the most current version on REAL Software's web site, http://www.realsoftware.com.

The PostgreSQL plug-in supports MD5 password authentication.

A field specified as type Float is actually implemented by postgreSQL as a double (8 bytes).

The IsPrimary column of the FieldSchema for a postgreSQL database always returns False.

PostgreSQL dates: field types Date, Time, and TimeStamp are now properly supported; use the DateColumn and DateValue methods for a date representation of this data, or use StringValue to get a human-readable date and/or time.

Large Objects

PostgreSQLDatabase implements PostgreSQL's large objects. PostgreSQL requires that all large object operations be performed inside of a transaction. Therefore, you must start a transaction before you perform your first large object operation, like this:

db.SQLExecute "BEGIN TRANSACTION"

After you have performed your last large object operation, you should close the transaction, like this:

db.SQLExecute "END TRANSACTION"

Please see the PostgreSQLLargeObject class for information on how to work with large objects.

Listen and Notify Protocol

The PostgreSQLDatabase class implements the listen and notify protocol of PostgreSQL databases.

To send a notification, call the PostgreSQLDatabase.Notify method with the name of the notification you want to send. For example, if you wanted to send a notification called "Hello World", you would call Notify like this:

Dim db as New PostgreSQLDatabase //connection code here db.Notify "Hello World"

To check for notifications, call the PostgreSQLDatabase.CheckForNotifications method. You will receive notifications as a PostgreSQLDatabase.ReceivedNotification event. The ReceivedNotification event is called with three arguments: the name of the notification as a String, the ID of the process sending the notification as an Integer, and an extra argument that the PostgreSQL documentation says is not used at this time. The name parameter is the same name that you used with the Notify method.

If you would like to check for notifications automatically, at some set interval, then use a Timer and call CheckForNotifications in the Timer's Action event.

In order to implement the ReceivedNotification event, you will need to either instantiate a PostgreSQLDatabase object on a Window, or you will need to subclass PostgreSQLDatabase.

Accompanying the PostgreSQL plug-in are two simple projects, Notify and Listen, that demonstrate how to send notifications and how to listen for them. Listen implements ReceivedNotification by instantiating a PostgreSQLDatabase object on Window1.

Examples

This example opens an existing PostgreSQL database.

Dim db as PostgreSQLDatabase db=New PostgreSQLDatabase db.host="192.168.1.172" db.port=5432 db.DatabaseName="myDatabase" db.Username="Charlie" db.Password="mashie" If db.connect then  //proceed with database operations else MsgBox "The connection failed." end if

See Also

Database, DatabaseRecord, PostgreSQLLargeObject, RecordSet classes.