ASP.NET Web Pages (Razor) Exit Code Block - asp.net

Question

Does anybody know how to exit a code block without interrupting page load in ASP.NET Web Page (Razor) in VB language? Let's say I have a login mechanism that execute in the following order:
Before page load:
Check if user id exist.
Check if password match.
if the user id does not exist, display error message then skip password validation and let the rest of the html page (body, footer) load. My current solution is to use VB specific GoTo.. statement which I think is ugly. Does anybody has a more elegant solution? Below is a simple sample code:
#Code
dim login As New clsLogin 'assume this class handles login validation
dim inputUserID As String 'this variable hold user id entered by user
dim inputPwd As String 'this is password entered by user
'First, check if that ID exist in database
if login.userExist(inputUserID) = false then
#<p>User does not exist !</p>
GoTo skip
End If
'If ID exist, check if password match
if login.checkPwd(inputUserID, inputPwd) = false then
#<p>Password Mismatch !</p>
GoTo skip
End If
'Passes all validation, display success message
#<p>Login Successful !</p>
skip:
End Code
I tried to replace the GoTo statement with return statement. However, it also stopped the page loading. I put the validation server code before any HTML is displayed and if I use return statement it wont show the HTML page. Any idea? Thanks in advance.

Answer 1

Short answer could use a function:
#Functions
function Check(byval inputUserID as integer, byval inputPwd as string) as string
dim login As New clsLogin 'assume this class handles login validation
dim result as string = string.Empty
'First, check if that ID exist in database
if login.userExist(inputUserID) = false then
return "User does not exist !"
End If
'If ID exist, check if password match
if login.checkPwd(inputUserID, inputPwd) = false then
return "Password Mismatch !"
End If
return result
end function
End functions
#Code
dim inputUserID As String 'this variable hold user id entered by user
dim inputPwd As String 'this is password entered by user
dim msg = #Check(inputUserID,inputPwd)
'Passes all validation, display success message
if string.isnullorempty(msg) then
msg = "<p>Login Successful !</p>"
end if
#msg
End Code
Hoever reading your comment seems you are looking for an elegant and sustainable solution, so I think you could approach your problem with a loosely coupled ValidationManager:
VB (translated with Telerik code converted)
Public Interface ILoginProvider
Function UserExist(inputUserID As Integer) As Boolean
Function CheckPwd(inputUserID As Integer, inputPwd As String) As Boolean
End Interface
Public Class LoginProvider
Implements ILoginProvider
Public Function UserExist(inputUserID As Integer) As Boolean
Return True
End Function
Public Function CheckPwd(inputUserID As Integer, inputPwd As String) As Boolean
Return True
End Function
End Class
Public Class ValidationResult
Public Property Result() As Boolean
Get
Return m_Result
End Get
Set
m_Result = Value
End Set
End Property
Private m_Result As Boolean
Public Property ResultMessage() As String
Get
Return m_ResultMessage
End Get
Set
m_ResultMessage = Value
End Set
End Property
Private m_ResultMessage As String
End Class
Public MustInherit Class Validator
Protected _provider As ILoginProvider
Protected _inputUserID As Integer
Protected _inputPwd As String
Public Sub New(provider As ILoginProvider, inputUserID As Integer, inputPwd As String)
_provider = provider
_inputPwd = inputPwd
_inputUserID = inputUserID
End Sub
Public MustOverride Function Validate() As ValidationResult
End Class
Public Class UserExistenceValidator
Inherits Validator
Public Sub New(provider As LoginProvider, inputUserID As Integer, inputPwd As String)
MyBase.New(provider, inputUserID, inputPwd)
End Sub
Public Overrides Function Validate() As ValidationResult
Dim result = New ValidationResult()
Dim check = _provider.UserExist(_inputUserID)
result.Result = check
If Not check Then
result.ResultMessage = "User Doesn't exist"
End If
Return result
End Function
End Class
Public Class UserPasswordValidator
Inherits Validator
Public Sub New(provider As LoginProvider, inputUserID As Integer, inputPwd As String)
MyBase.New(provider, inputUserID, inputPwd)
End Sub
Public Overrides Function Validate() As ValidationResult
Dim result = New ValidationResult()
Dim check = _provider.CheckPwd(_inputUserID, _inputPwd)
result.Result = check
If Not check Then
result.ResultMessage = "Wrong Password"
End If
Return result
End Function
End Class
Public Class ValidationManager
Private _validators As List(Of Validator)
Public Sub New()
_validators = New List(Of Validator)()
End Sub
Public Function Validate() As ValidationResult
Dim result As ValidationResult = Nothing
For Each item As var In _validators
result = item.Validate()
If Not result.Result Then
Return result
End If
Next
Return New ValidationResult() With { _
Key .Result = True, _
Key .ResultMessage = "Successfull validated" _
}
End Function
End Class
C#
public interface ILoginProvider
{
bool UserExist(int inputUserID);
bool CheckPwd(int inputUserID, string inputPwd);
}
public class LoginProvider: ILoginProvider
{
public bool UserExist(int inputUserID)
{
return true;
}
public bool CheckPwd(int inputUserID, string inputPwd)
{
return true;
}
}
public class ValidationResult
{
public bool Result { get; set; }
public string ResultMessage { get; set; }
}
public abstract class Validator
{
protected ILoginProvider _provider;
protected int _inputUserID;
protected string _inputPwd;
public Validator(ILoginProvider provider, int inputUserID, string inputPwd)
{
_provider = provider;
_inputPwd = inputPwd;
_inputUserID = inputUserID;
}
public abstract ValidationResult Validate();
}
public class UserExistenceValidator : Validator
{
public UserExistenceValidator(LoginProvider provider,int inputUserID, string inputPwd): base(provider,inputUserID, inputPwd)
{
}
public override ValidationResult Validate()
{
var result = new ValidationResult();
var check = _provider.UserExist(_inputUserID);
result.Result = check;
if(!check)
result.ResultMessage = "User Doesn't exist";
return result;
}
}
public class UserPasswordValidator : Validator
{
public UserPasswordValidator(LoginProvider provider, int inputUserID, string inputPwd)
: base(provider, inputUserID, inputPwd)
{
}
public override ValidationResult Validate()
{
var result = new ValidationResult();
var check = _provider.CheckPwd(_inputUserID, _inputPwd);
result.Result = check;
if (!check)
result.ResultMessage = "Wrong Password";
return result;
}
}
public class ValidationManager
{
List<Validator> _validators;
public ValidationManager()
{
_validators = new List<Validator>();
}
public ValidationResult Validate()
{
ValidationResult result = null;
foreach (var item in _validators)
{
result = item.Validate();
if(!result.Result)
return result;
}
return new ValidationResult(){Result = true,ResultMessage="Successfull validated" };
}
}
Use
#Function Check() As string
Dim login As New clsLogin 'assume this class handles login validation
Dim inputUserID As String 'this variable hold user id entered by user
Dim inputPwd As String 'this is password entered by user
Dim login As New LoginProvider()
Dim validators = New List(Of Validator)()
validators.Add(New UserExistenceValidator(login, 1, "test1"))
validators.Add(New UserPasswordValidator(login, 1, "test1"))
Dim manager = New ValidationManager(validators)
Dim result = manager.Validate()
return string.format("<p>{0}</p>",result.ResultMessage)
End Function
#Code
#Check()
End Code

Answer 2

Found it! Thx to InvernoMuto to show me how to define functions inside webpage.
First I created a class to hold login result that can provide reason if login fails.
Class LoginResult
Public Property LoginSuccess As Boolean
Public Property Reason As String
End Class
Then I created the following function for login validations
#Functions
Function CheckLogin(User As String, Pwd as String) As LoginResult
dim login As New clsLogin
Dim res as New LoginResult
res.LoginSuccess = True
if login.userExist(inputUserID) = false then
res.LoginSuccess = False
res.Reason = "User does not exist !"
return res
end if
if login.checkPwd(inputUserID, inputPwd) = false then
res.LoginSuccess = False
res.Reason = "Password mismatch !"
return res
end if
return res
End Function
End Functions
Then on the Login HTML page I just call the following code:
dim lr as LoginResult
lr = CheckLogin("someone", "password")
if lr.LoginSuccess = True then
#<p>Login Success !</p>
else
#<p>Error: #lr.Reason</p>
end if