Identify the properties of an object and put values into it - vb.net

Question

I want to identify the properties of specific object that it receives when the method is called and put values in it from the db result that I got. I've searched about it but I'm currently stucked in how I should proceed from here. Here is my code..
Public Class DBModel
Public Sub getFromDB(ByRef lists As List(Of Object), ByVal classType As Type, ByVal tblName as String)
Dim strSql As String = "SELECT * FROM " & tblName
Dim props = classType.GetProperties()
Try
Using cnn As New SqlConnection("Data Source = .\; Initial Catalog = DBName;" & "Integrated Security = True;")
Using cmd As New SqlCommand(strSql, cnn)
cnn.Open()
Using dr As SqlDataReader = cmd.ExecuteReader()
While dr.Read
For Each prop In props
For i As Integer = 0 To dr.VisibleFieldCount - 1
prop = dr.GetValue(i)
Next
Next
lists.Add(props)
End While
End Using
End Using
End Using
Catch e As Exception
MessageBox.Show(e.ToString())
End Try
End Sub
End Class
I'm calling here the getFromDB method to populate the list of customers in this class, but I'll also call the getFromDB method from other classes with another different set of properties..
Public Class CustomerCtrler
private _CustomerList As New List(Of Customer)
Public Sub New()
Dim dbModel As New DBModel
Dim cust As New Customer
dbModel.getFromDB(_CustomerList, cust.GetType, "CustTbl")
End sub
End Class
Public Class Customer
Public Property custID As Integer
Public Property FirstName As String
Public Property LastName As String
Public Property DateRegistered As DateTime
End Class
But I got a InvalidCastException, so I've searched about converting the data types but I got: "Value type of Integer cannot be converted into PropertyInfo" at the 'prop = dr.GetValue(i)' line..
I'm quite new to object oriented programming so I'm sorry if there's a lot of mistakes there but your help will be really appreciated..

Answer 1

I would tend to go with something like this:
Public Function GetListFromDatabase(Of T As New)(tableName As String) As List(Of T)
Dim itemType = GetType(T)
Dim allProperties = itemType.GetProperties()
Dim items As New List(Of T)
Using connection As New SqlConnection("connection string here"),
command As New SqlCommand($"SELECT * FROM [{tableName}]", connection)
connection.Open()
Using reader = command.ExecuteReader()
Dim columnNames = reader.GetColumnSchema().
Select(Function(column) column.ColumnName).
ToArray()
'Ignore properties that don't have a corresponding column.
Dim properties = allProperties.Where(Function(prop) columnNames.Contains(prop.Name)).
ToArray()
Do While reader.Read()
'We can do this because we have specified that T must have a
'parameterless constructor by using "As New" in the method declaration.
Dim item As New T
For Each prop In properties
prop.SetValue(item, reader(prop.Name))
Next
items.Add(item)
Loop
End Using
End Using
Return items
End Function
You can then do this:
_CustomerList = dbModel.GetListFromDatabase(Of Customer)("CustTbl")
You can obviously create a variation on that if you really want to pass in an existing list but I don't see the point in that unless the list might already contain items.
EDIT: Here is an alternative method to get the data reader column names. I haven't tested it so it may be that "COLUMN_NAME" isn't quite right but it will be something very close to this:
Dim schemaTable = reader.GetSchemaTable()
Dim columnNames = schemaTable.Rows.
Cast(Of DataRow).
Select(Function(row) CStr(row("COLUMN_NAME"))).
ToArray()