Upload to database in asp.net - asp.net

Question

I am trying to upload files to database but it is giving me an null exception error
Here is the error:
System.NullReferenceException: Object reference not set to an instance of an object.
Can anybody help me finding the error:
Here is aspx code
<div>
<asp:FileUpload ID="FileUpload1" runat="server" />
<asp:Button ID="btnUpload" runat="server" Text="Upload" OnClick="Upload" />
<hr />
<asp:GridView ID="GridView1" runat="server" HeaderStyle-BackColor="#3AC0F2" HeaderStyle-ForeColor="White"
RowStyle-BackColor="#A1DCF2" AlternatingRowStyle-BackColor="White" AlternatingRowStyle-ForeColor="#000"
AutoGenerateColumns="false">
<Columns>
<asp:BoundField DataField="Name" HeaderText="File Name"/>
<asp:TemplateField ItemStyle-HorizontalAlign = "Center">
</asp:TemplateField>
</Columns>
</asp:GridView>
</div>
Here is the code behind:
using System;
using System.IO;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
public partial class DatabaseDownload : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
}
protected void Upload(object sender, EventArgs e)
{
string filename = Path.GetFileName(FileUpload1.PostedFile.FileName);
string contentType = FileUpload1.PostedFile.ContentType;
using (Stream fs = FileUpload1.PostedFile.InputStream)
{
using (BinaryReader br = new BinaryReader(fs))
{
byte[] bytes = br.ReadBytes((Int32)fs.Length);
string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
using (SqlConnection con = new SqlConnection(constr))
{
string query = "insert into tblFiles values (#Name, #ContentType, #Data)";
using (SqlCommand cmd = new SqlCommand(query))
{
cmd.Connection = con;
cmd.Parameters.AddWithValue("#Name", filename);
cmd.Parameters.AddWithValue("#ContentType", contentType);
cmd.Parameters.AddWithValue("#Data", bytes);
con.Open();
cmd.ExecuteNonQuery();
con.Close();
}
}
}
}
Response.Redirect(Request.Url.AbsoluteUri);
}
}

Answer 1

If your connection named as
<add name="DefaultConnection" ...
then you can obtain its value using same key (DefaultConnection)
string constr = ConfigurationManager.ConnectionStrings["DefaultConnection"].ConnectionString;
Now if for some reasons that db does not work (perhaps you delete the DB file, etc) you can try to fixe it by deleting DB. Do this from the command line. Open the "Developer Command Propmpt for VisualStudio" under your "Start/Programs menu->All Programs->Visual Studio 2012->Visual Studio Tools"
Run the following commands:
sqllocaldb.exe stop v11.0
sqllocaldb.exe delete v11.0
Now execute "update-database" command from package manager console and it will create database for you without any obstacles.