Convert a DataReader to DataTable in ASP.NET

A DataReader is a read-only forward-only way of reading data. It is quiet fast when compared to fetching data using a DataSet. Infact internally, a DataSet uses a DataReader to populate itself. However at times, we need the best of both worlds.

A dataset/datatable is extremely handy when it comes to binding it to a control like a GridView. So to make use of both the DataReader and DataTable in the same solution, we can fetch the data using a DataReader and then convert it to a DataTable and bind it to the control. In this article, we will explore how to do the conversion using two approaches; the first one, a direct method by using the DataTable.Load() and the second one, by manually converting a DataReader to a DataTable.

Step 1: Create a new ASP.NET application. Drag and drop two GridView controls to the page. We will fetch data from a DataReader into a DataTable and bind the DataTable to the GridView’s. Before moving ahead, add a web.config file to the project and add the following element.

<connectionStrings> 
    <addname="NorthwindConn"connectionString="Data Source=(local); Initial Catalog=Northwind; Integrated Security=true;"/> 
</connectionStrings> 

 Step 2: Let us first see how to convert a DataReader to a DataTable using the easy way out. DataTable in ADO.NET 2.0 contains a Load() method which enables the DataTable to be filled using a IDataReader. This method is quiet handy when you need to quickly create a DataTable, without using a DataAdapter!! Let us see how.

C#

private void ConvertDateReadertoTableUsingLoad()
{
    SqlConnection conn = null;
    try
    {
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConn"].ConnectionString;
        conn = new SqlConnection(connString);
        string query = "SELECT * FROM Customers";
        SqlCommand cmd = new SqlCommand(query, conn);
        conn.Open();

        SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
        DataTable dt = new DataTable();
        dt.Load(dr);

        GridView1.DataSource = dt;
        GridView1.DataBind();

    }

    catch (SqlException ex)
    {
        // handle error 
    }

    catch (Exception ex)
    {
        // handle error 
    }

    finally
    {
        conn.Close();
    }
}

VB.NET

Private Sub ConvertDateReadertoTableUsingLoad()
    Dim conn As SqlConnection = Nothing
    Try
        Dim connString As String = ConfigurationManager.ConnectionStrings("NorthwindConn").ConnectionString
        conn = New SqlConnection(connString)
        Dim query As String = "SELECT * FROM Customers"
        Dim cmd As SqlCommand = New SqlCommand(query, conn)
        conn.Open()

        Dim dr As SqlDataReader = cmd.ExecuteReader(CommandBehavior.CloseConnection)
        Dim dt As DataTable = New DataTable()
        dt.Load(dr)
        GridView1.DataSource = dt
        GridView1.DataBind()

    Catch ex As SqlException
        ' handle error 
    Catch ex As Exception
        ' handle error 
    Finally
        conn.Close()
    End Try
End Sub

Note 1: If there is some existing data in the DataTable, the data coming from the DataReader is merged with the existing rows.

Note 2: If you need a DataReader back from a DataTable, use the DataTable.CreateDataReader() method.

Step 3: The method shown in the Step 2 was the easy way out. However, if for some reason(if you are not using ADO.NET 2.0), you would want to convert a DataReader to a DataTable ‘manually’, here’s the code. In the code below, a DataTable schema is created first using the GetSchemaTable() method of DataReader. The GetSchemaTable() returns a DataTable describing the column metadata of the IDataReader. Once done, we loop through the rows of the schema table and create a DataColumn object and set its properties. This DataColumn is also added to the List<> collection. We then read rows from the DataReader and populate the DataTable.

C#

private void ConvertDataReaderToTableManually()
{
    SqlConnection conn = null;
    try
    {
        string connString = ConfigurationManager.ConnectionStrings["NorthwindConn"].ConnectionString;
        conn = new SqlConnection(connString);
        string query = "SELECT * FROM Customers";
        SqlCommand cmd = new SqlCommand(query, conn);
        conn.Open();

        SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
        DataTable dtSchema = dr.GetSchemaTable();
        DataTable dt = new DataTable();
        // You can also use an ArrayList instead of List<> 
        List<DataColumn> listCols = new List<DataColumn>();
        if (dtSchema != null)
        {
            foreach (DataRow drow in dtSchema.Rows)
            {
                string columnName = System.Convert.ToString(drow["ColumnName"]);
                DataColumn column = new DataColumn(columnName, (Type)(drow["DataType"]));
                column.Unique = (bool)drow["IsUnique"];
                column.AllowDBNull = (bool)drow["AllowDBNull"];
                column.AutoIncrement = (bool)drow["IsAutoIncrement"];
                listCols.Add(column);
                dt.Columns.Add(column);
            }

        }

        // Read rows from DataReader and populate the DataTable 

        while (dr.Read())
        {
            DataRow dataRow = dt.NewRow();
            for (int i = 0; i < listCols.Count; i++)
            {
                dataRow[((DataColumn)listCols[i])] = dr[i];
            }

            dt.Rows.Add(dataRow);
        }

        GridView2.DataSource = dt;
        GridView2.DataBind();
    }

    catch (SqlException ex)
    {
        // handle error 
    }

    catch (Exception ex)
    {
        // handle error 
    }

    finally
    {
        conn.Close();
    }
}

VB.NET

    Private Sub ConvertDataReaderToTableManually()
        Dim conn As SqlConnection = Nothing
        Try
            Dim connString As String = ConfigurationManager.ConnectionStrings("NorthwindConn").ConnectionString
            conn = New SqlConnection(connString)
            Dim query As String = "SELECT * FROM Customers"
            Dim cmd As SqlCommand = New SqlCommand(query, conn)
            conn.Open()

            Dim dr As SqlDataReader = cmd.ExecuteReader(CommandBehavior.CloseConnection)
            Dim dtSchema As DataTable = dr.GetSchemaTable()
            Dim dt As DataTable = New DataTable()
            ' You can also use an ArrayList instead of List<> 
            Dim listCols As List(Of DataColumn) = New List(Of DataColumn)()
            If Not dtSchema Is Nothing Then
                For Each drow As DataRow In dtSchema.Rows
                    Dim columnName As String = System.Convert.ToString(drow("ColumnName"))
                    Dim column As DataColumn = New DataColumn(columnName, CType(drow("DataType"), Type))
                    column.Unique = CBool(drow("IsUnique"))
                    column.AllowDBNull = CBool(drow("AllowDBNull"))
                    column.AutoIncrement = CBool(drow("IsAutoIncrement"))
                    listCols.Add(column)
                    dt.Columns.Add(column)
                Next drow
            End If

            ' Read rows from DataReader and populate the DataTable 

            Do While dr.Read()
                Dim dataRow As DataRow = dt.NewRow()
                For i As Integer = 0 To listCols.Count - 1
                    dataRow((CType(listCols(i), DataColumn))) = dr(i)
                Next i
                dt.Rows.Add(dataRow)
            Loop

            GridView2.DataSource = dt
            GridView2.DataBind()
        Catch ex As SqlException
            ' handle error 
        Catch ex As Exception
            ' handle error 
        Finally
            conn.Close()
        End Try


    End Sub

Step 4: Call the two methods on the PageLoad()

C#

protected void Page_Load(object sender, EventArgs e)
{
    ConvertDateReadertoTableUsingLoad();
    ConvertDataReaderToTableManually();
} 

VB.NET

Protected Sub Page_Load(ByVal sender As Object, ByVal e As EventArgs) 
    ConvertDateReadertoTableUsingLoad() 
    ConvertDataReaderToTableManually() 
End Sub 

The DataTable.Load(IDataReader) is extremely handy when you want to quickly bind the data coming from a DataReader to a control like the GridView. The DataTable.Load() method has three overloads. We have explored one of them. I would encourage you to explore the other two over here.

I hope this article was useful and I thank you for viewing it.

This article has been editorially reviewed by Suprotim Agarwal.

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Suprotim Agarwal, MCSD, MCAD, MCDBA, MCSE, is the founder of DotNetCurry, DNC Magazine for Developers, SQLServerCurry and DevCurry. He has also authored a couple of books 51 Recipes using jQuery with ASP.NET Controls and The Absolutely Awesome jQuery CookBook.

Suprotim has received the prestigious Microsoft MVP award for Fifteen consecutive years. In a professional capacity, he is the CEO of A2Z Knowledge Visuals Pvt Ltd, a digital group that offers Digital Marketing and Branding services to businesses, both in a start-up and enterprise environment.

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