Thread: Global Error Class

In order to catch errors etc. I thought I'd create a global error class that I could drop any errors (mainly db errors) into.

So in a globalBLL I have:-

Code:

Namespace MyApp.App.BLL.Globals
    Public Class MyAppError
#Region "Private Variables"
        Private _err As String = String.Empty
#End Region
#Region "Properties"
        Public Property err() As String
            Get
                Return _err
            End Get
            Set(ByVal value As String)
                _err = value
            End Set
        End Property
#End Region
#Region "Constructors"
        Public Sub New()
        End Sub
        Public Sub New(ByVal _Err As String)
            Me.err = _Err
        End Sub
#End Region
    End Class
 
End Namespace

Then I have an AddUser function in my DAL

Code:

        Public Shared Function AddUser(ByVal user As MyAppUser, ByVal ref As Integer) As Boolean
 
            Dim myErr as New MyAppError
            Dim conn As New MySqlConnection(ConnDAL.connString)
            Dim mycomm As New MySqlCommand("AddUser", conn)
            mycomm.CommandType = Data.CommandType.StoredProcedure
            Using conn
                Using mycomm
                    Try
                        Dim salt As String = CreateSalt(8)
                        mycomm.Parameters.Add(New MySqlParameter("username", user.username))
                        mycomm.Parameters.Add(New MySqlParameter("pwdHash", CreatePasswordHash(user.pwdHash, salt)))
                        mycomm.Parameters.Add(New MySqlParameter("pwdSalt", salt))
                        mycomm.Parameters.Add(New MySqlParameter("access", user.accessI))
                        mycomm.Parameters.Add(New MySqlParameter("forename", user.forename))
                        mycomm.Parameters.Add(New MySqlParameter("surname", user.surname))
                        Dim pAdd1 As MySqlParameter = mycomm.Parameters.Add("add1", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.add1) Then
                            pAdd1.Value = DBNull.Value
                        Else
                            pAdd1.Value = user.add1
                        End If
                        Dim pAdd2 As MySqlParameter = mycomm.Parameters.Add("add2", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.add2) Then
                            pAdd2.Value = DBNull.Value
                        Else
                            pAdd2.Value = user.add2
                        End If
                        Dim pAdd3 As MySqlParameter = mycomm.Parameters.Add("add3", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.add3) Then
                            pAdd3.Value = DBNull.Value
                        Else
                            pAdd3.Value = user.add3
                        End If
                        Dim pCity As MySqlParameter = mycomm.Parameters.Add("city", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.city) Then
                            pCity.Value = DBNull.Value
                        Else
                            pCity.Value = user.city
                        End If
                        Dim pCounty As MySqlParameter = mycomm.Parameters.Add("county", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.county) Then
                            pCounty.Value = DBNull.Value
                        Else
                            pCounty.Value = user.county
                        End If
                        Dim pPostcode As MySqlParameter = mycomm.Parameters.Add("postcode", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.postcode) Then
                            pPostcode.Value = DBNull.Value
                        Else
                            pPostcode.Value = user.postcode
                        End If
                        Dim pTelno1 As MySqlParameter = mycomm.Parameters.Add("telno1", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.telno1) Then
                            pTelno1.Value = DBNull.Value
                        Else
                            pTelno1.Value = user.telno1
                        End If
                        Dim pTelno2 As MySqlParameter = mycomm.Parameters.Add("telno2", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.telno2) Then
                            pTelno2.Value = DBNull.Value
                        Else
                            pTelno2.Value = user.telno2
                        End If
                        Dim pFaxno1 As MySqlParameter = mycomm.Parameters.Add("faxno1", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.faxno1) Then
                            pFaxno1.Value = DBNull.Value
                        Else
                            pFaxno1.Value = user.faxno1
                        End If
                        Dim pEmail As MySqlParameter = mycomm.Parameters.Add("email", MySqlDbType.VarChar)
                        If String.IsNullOrEmpty(user.email) Then
                            pEmail.Value = DBNull.Value
                        Else
                            pEmail.Value = user.email
                        End If
                        Dim pAddedby As MySqlParameter = mycomm.Parameters.Add("addedby", MySqlDbType.Int16)
                        pAddedby.Value = ref
                        Dim pUserref As MySqlParameter = mycomm.Parameters.Add("ref", MySqlDbType.Int16)
                        pUserref.Direction = Data.ParameterDirection.Output
                        conn.Open()
                        mycomm.ExecuteNonQuery()
                        user.ref = pUserref.Value
                    Catch ex As Exception
                        myErr.err = ex.ToString
                    Finally
                        mycomm.Dispose()
                        conn.Close()
                        conn.Dispose()
                    End Try
                End Using
            End Using
 
            If String.IsNullOrEmpty(myErr.err) Then
                Return True
            Else
                Return False
            End If
 
        End Function

But I can't then obviously get the error instance in the page that called the function. Previously I had an err property in each class I created. Just wondered if there was a global way of handling this?

Ideally, you would have a base class that all of your other BLL classes would inherit. The base class would have all the methods and properties that should be available to all of these classes via inheritence.

So something like?

Code:

Public Class MyAppUser
Inherits MyAppError

Right, but I'd make 'MyAppError' more generic so it would look like it contains methods other than error handling. For example, I name my base class "BizObject".

Originally Posted by jmurrayhead

Right, but I'd make 'MyAppError' more generic so it would look like it contains methods other than error handling. For example, I name my base class "BizObject".

I see...Gotcha...

Take a look here, for more information: http://www.developerbarn.com/blogs/j...ase-class.html

How do you deal with List(Of ) methods?

For example, if I have in a page:-

Code:

Dim UserList as List(Of MyAppUser) = MyAppUser.GetUserList()

As your GetUserList is not a class, it doesn't inherit the global err class, so you can't set this value in the GetUserList DAL function.

How do you deal with errors in a List(Of ) method?

Code:

Try
    Dim UserList as List(Of MyAppUser) = MyAppUser.GetUserList()
Catch ex As Exception
    DisplayError(ex.Message.ToString)
End Try

Not sure why you would go through the effort of creating a completely new error class, when you could use either of the following:

1) The pages Page_Error event as seen below:

Code:

Private Sub Page_Error(ByVal sender As Object, ByVal e As System.EventArgs) 
Handles MyBase.Error
  Handle Your Errors Here    
End Sub

2) The Applications Application_Error event in the Global.asax file, as seen below:

Code:

Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
    Handle Your Errors Here 
End Sub

Hmm..I've not read anything about using Page_Error before. Sounds like it might work. I could also use it to email me any errors, which is what my Classic ASP site did...

Would that also pick up errors from application layers? ie a Data Access Layer and a Business Logic Layer...

If I had this, for example:-
In a Data Access Layer

Code:

Public Shared Function GetSomething(ByVal ref as integer) as Something
  try
      conn.open
      rs = mycomm.executereader
 
  Catch ex As Exception
     'Would it pick up this error
  End Try

Also, could you just have it in a Master Page and it pick up errors from all .aspx pages, or would one in the master page only pick up errors in the master page?

If there is an error does it process the rest of the page or stop processing?

The thing I like about the way I've done it above is being able to pass an error message back to the page like, "An error occurred whilst building the Client List", for example. Can you do something like that with this method?

Sorry for all the questions. I've not used this before so before I start changing from something I'm used to, I'd just like more of an insight with how it works and what you can and can't do with it.