Populate class from query on VB Net - vb.net

Question

Help translate C# code from this link Simplest way to populate class from query in C# to VB Net.
Option Infer On
Imports System.Reflection
Private Sub Main()
Dim connectionString = "..."
Dim records = (New Query(connectionString)).SqlQuery(Of TVChannel)("select top 10 * from TVChannel")
End Sub
Private Class TVChannel
Public Property number() As String
Public Property title() As String
Public Property favoriteChannel() As String
Public Property description() As String
Public Property packageid() As String
Public Property format() As String
End Class
Public Class Query
Private ReadOnly _connectionString As String
Public Sub New(ByVal connectionString As String)
_connectionString = connectionString
End Sub
Public Function SqlQuery(Of T)(ByVal query As String) As List(Of T)
Dim result = New List(Of T)()
Using connection = New SqlConnection(_connectionString)
connection.Open()
Using command = connection.CreateCommand()
command.CommandText = query
Using reader = command.ExecuteReader()
Dim columns = Enumerable.Range(0, reader.FieldCount).Select(Function(f) reader.GetName(f)).ToArray()
Dim properties = GetType(T).GetProperties()
Do While reader.Read()
Dim data = New Object(reader.FieldCount - 1){}
reader.GetValues(data)
Dim instance = DirectCast(Activator.CreateInstance(GetType(T)), T)
For i = 0 To data.Length - 1
If data(i) Is DBNull.Value Then
data(i) = Nothing
End If
Dim [property] = properties.SingleOrDefault(Function(x) x.Name.Equals(columns(i), StringComparison.InvariantCultureIgnoreCase))
If [property] IsNot Nothing Then
[property].SetValue(instance, Convert.ChangeType(data(i), [property].PropertyType))
End If
Next i
result.Add(instance)
Loop
End Using
End Using
End Using
Return result
End Function
End Class
but, I got error on this line
Dim instance = DirectCast(Activator.CreateInstance(GetType(T)), T)
System.MissingMethodException: 'No parameterless constructor defined for this object.'

Answer 1

This is a much better pattern to follow. It addresses at least four issues in the original code (sql injection, Nothing vs null, constructor access, unnecessary allocations):
Public Module SQL
Private ReadOnly _connectionString As String = "..."
Public Iterator Function Query(Of T)(ByVal query As String, translate As Func(IDataRecord, T), ParamArray data() As SqlParameter) As IEnumerable(Of T)
Using connection As New SqlConnection(_connectionString), _
command As New SqlCommand(query, connection)
If data IsNot Nothing Then command.Parameters.AddRange(data)
connection.Open()
Using reader As SqlDataReader = command.ExecuteReader()
While reader.Read()
Yield translate(reader)
End While
reader.Close()
End Using
End Using
End Function
End Module
Call it like this:
Private Sub Main()
Dim records = SQL.Query("select top 10 * from TVChannel",
Function(r)
'Yes, you're doing the mapping manually now for each query.
'But this lets you properly account for things NULL, column name mismatches, computed properties, etc.
Return New TVChannel With {
.number = r["number"],
.title = r["title"],
.favoriteChannel = r["favoriteChannel"],
.description = r["description"],
.packageid = r["packageid"],
.format = r["format"]
}
End Function,
Nothing)
For Each channel As TVChannel In records
Console.WriteLine($"Channel {channel.number}, {channel.title}")
Next
End Sub