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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).
Component
Component Name
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USMAIL
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Component Prog ID
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UsMail.Class1
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Method Name
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CHECK_ADDRESS_EXE
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Physical Method Name
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checkAddress
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Parameters of RESOLVE_ADDRESS
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In - String
Return - Long Integer
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Query protocol assocation
Component Name
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USMAIL
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Protocol Name
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CHECK_ADDRESS
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Exe Method Name
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CHECK_ADDRESS_EXE
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Constraint
Constraint Name
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CHECK_EMAIL
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Message
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Email address is not correct.
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Transition Table
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(null)
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Fire on Insert
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(null)
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Fire on Delete
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(null)
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Fire on Update
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(null)
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Set the SQL statement to:
INVOKE usmail.check_address WITH
SELECT email
FROM person
WHERE email is not null
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Code of invoked subprogram
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
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See also
Using RDMI
Rules-Driven Method Invocation (RDMI)
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