How can I read from a DataRow or a DataReader using the same code?

问题

Currently, I am using a SqlDataReader loaded up with a simple database 'Select' query. Each row represents a domain object, so I inflate each object like this:

Dim loadedItems As New List(Of Item)
Dim dr As SqlDataReader = GetItemsDataReader()
While dr.Read()
  Dim item As Item = GetItemFromData(dr)
  loadedItems.Add(item)
End While

The GetItemFromData method I wrote looks something like this:

Private Function GetItemFromData(dr As SqlDataReader) As Item
  Dim loadedItem As New Item()
  loadedItem.ID = dr("ID")
  loadedItem.Name = dr("Name")
  'etc., etc.'
  Return loadedItem
End Function

In some cases, I have to read data from a DataRow instead of a SqlDataReader. But the code would be the exact same! As I look at my GetItemFromData method, I want to accept a more generic type of object in the dr parameter so that I can treat a DataReader the same as a DataRow, since I would be writing the exact same code inside the method if I wrote one that was meant to use a DataRow. Is there a way to do that?

回答1:

Only way I can think of off the top of my head would be to wrap a few classes and implement an inferface - something like:

Interface IIndexer
    Default ReadOnly Property Item(ByVal index As String)
End Interface

Class DataReaderWrapper
    Implements IIndexer

    Private ReadOnly _reader As IDataReader

    Public Sub New(reader As IDataReader)
        _reader = reader
    End Sub

    Public ReadOnly Property Item(index As String) As Object Implements IIndexer.Item
        Get
            Return _reader(index)
        End Get
    End Property
End Class

Class DataRowWrapper
    Implements IIndexer

    Private ReadOnly _row As DataRow

    Public Sub New(row As DataRow)
        _row = row
    End Sub

    Public ReadOnly Property Item(index As String) As Object Implements IIndexer.Item
        Get
            Return _row(index)
        End Get
    End Property
End Class

You would then have to wrap your row or reader before passing it to your method:

Private Function GetItemFromData(indexer As IIndexer) As Item
    Dim loadedItem As New Item()
    loadedItem.ID = indexer("ID")
    loadedItem.Name = indexer("Name")
    'etc., etc.'
    Return loadedItem
End Function

Dim i As Item = GetItemFromData(New DataRowWrapper(dr))

回答2:

How about using a DataTable instead:

Dim DataTable table AS new DataTable()
table.Load(GetItemsDataReader())
foreach (DataRow row in table.Rows) {
   Dim item As Item = GetItemFromData(row)
   loadedItems.Add(item)
}

Change your GetItemFromData() method to take a DataRow instead of a DataReader (sorry about the VB.NET/C# hybrid pseudo code).

来源：https://stackoverflow.com/questions/7666943/how-can-i-read-from-a-datarow-or-a-datareader-using-the-same-code

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