Example 3: Checking an Email Address

This example shows how an external component checks if an email address string entered or changed by the user is known to a mail server.

This is an example of an invocative constraint implementing a restrictive business rule. The rule is that email addresses that do not exist in the address book of MS Exchange cannot be entered.

If this example is implemented in conjunction with example 2 (resolving the email address), then the constraint in example 2 will be evaluated before the constraint in example 3 since corrective constraints are evaluated before restrictive constraints. Normally if example 2 resolves the address successfully, then example 3 will not raise a violation. This is desired behavior.

The example uses the Travel Agency case (Expanded Version).

To try out this example:

•Locate the Samples/Usmail directory on your CD.

•Read the README.TXT file for information on installing, running and inspecting the sample component.

Component

USMAIL

Component Prog ID

UsMail.Class1

Method

CHECK_ADDRESS_EXE

Physical Method

checkAddress

Parameters of CHECK_ADDRESS_EXE

1, In, String

2, Return, Long Integer

Query Protocol

Component Name = USMAIL

Protocol Name = CHECK_ADDRESS

Exe Method Name = CHECK_ADDRESS_EXE

PERSON Table

Add an EMAIL column based on a regular CHAR(60) domain (On Oracle7: VARCHAR2).

Constraint

CHECK_EMAIL

Message: "Email address is not correct."

INVOKE    usmail.check_address

WITH

SELECT    email

FROM        person

WHERE        email is not null

Description of functionality:

The component establishes a connection to a Microsoft Exchange server using Microsoft's standard MAPI component. The exchange server returns a value indicating whether the address exists or not. The invoked component then returns 1 if the address is unknown (constraint violation), 0 if the address is correct, and -1 if an error occurs.

Visual Basic code of subprogram directly invoked by USoft:

Const USOFT_STATUS_VIOLATION = 1

Const USOFT_STATUS_NO_VIOLATION = 0

Const USOFT_STATUS_ERROR = -1

Public Function checkAddress(address As String, _

                                   Optional profile_name As String, _

                                   Optional password As String) _

                                   As Long

  Dim objSession As Object

  Dim objMessage As Object

  On Error GoTo on_error

  ' Initialize this function to return a violation

  checkAddress = USOFT_STATUS_VIOLATION

   If Len(address) = 0 Then

     checkAddress = USOFT_STATUS_NO_VIOLATION

     Exit Function

  End If

  Set objSession = newSession(profile_name:=profile_name, _

                                password:=password, _

                                no_mail:=True)

  ' Create a new message and check how the address will be resolved

  Set objMessage = newMessage(objSession, address)

  If Not resolveMsgAddress(objMessage) = USOFT_UNRESOLVED_ADDRESS Then

     ' Return absence of violation

     checkAddress = USOFT_STATUS_NO_VIOLATION

  End If

  cleanUp objSession, objMessage

  Exit Function

on_error:

  If Not ignoreError() Then

     showError "checkAddress"

     checkAddress = USOFT_STATUS_ERROR

  End If

  cleanUp objSession, objMessage

End Function