Question

I’m using the following function to map columns from a DataTable (passed from the data tier) to object properties. The function exists within the class I’m populating. The class has two methods: Load() which loads the object with values and LoadAll() which returns a collection of populated objects. I wanted to be able to use the same code to populate the current object or a new object. However I’m less than happy with the result, largely because of the duplication which is a bit of a maintenance nightmare.

Private Function MapDataRowToProperties(ByVal dr As DataRow, ByVal target As Incident) As Incident             If target.Equals(Me) Then                Me.ID = Convert.ToInt32(dr.Item('pkIncidentID'))                Me.Description = dr.Item('IncidentDetail').ToString                Me.Created = Convert.ToDateTime(dr.Item('CreatedOn'))                ...                Return Me            Else               Dim NewIncident As New Incident               NewIncident.ID = Convert.ToInt32(dr.Item('pkIncidentID'))               NewIncident.Description = dr.Item('IncidentDetail').ToString               NewIncident.Created = Convert.ToDateTime(dr.Item('CreatedOn'))               ...               Return NewIncident            End If      End Function 

Note: I’m well aware of ORM tools which will do this for me and I normally use EntitySpaces, but for this project I am unable to do so.

Answer 1

It appears to me that your If and Else blocks only differ in the fact that one assumes an existing object(the current instance) has been passed and the other overwrites any passed reference by creating it anew.

This would seem like an ideal case for a ByRef parameter, in other words, let the calling code pass different variables and let this function work in the same way in each case :

Private Sub MapDataRowToProperties(ByVal dr As DataRow, ByRef target As Incident)   If target Is Nothing Then     target = New Incident()   End If   'Set properties    '... End Sub 

Sample invocation :

'Usage 1: MapDataRowToProperties(dr, Me)  'Usage 2: Dim inc as New Incident() MapDataRowToProperties(dr, inc)