The type 'System.Data.Objects.ObjectContext' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data.Entity, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'

You receive this error because you have not used references in your project to use System.Data.Entity namespaces.

To including the Entity Framework in your application, you must have a reference to the System.Data.Entity namespace so that you have access to the core functionality of the Entity Framework. These classes enable you to query, insert, update, and delete data.

1. In Solution Explorer, right-click References and select Add Reference from the right-click menu.
2. The Reference Manager dialog box is displayed.
3. Select System.Data.Entity from the list in the dialog box and Click OK.

How to make single radio button selection in gridview using javascript

In ASP.Net the GridView control does not support selection of a single RadioButton that works as a group across rows. Here we will see how to select only one RadioButton in a GridView using javascript.

Step - 1  In the design drag ang drop a grid view control from the toolbox.
               Change the gridview according like below.
               <asp:GridView ID="grdDisply" runat="server" AutoGenerateColumns="false">
               <Columns>
                <asp:TemplateField HeaderText="Select">
                    <ItemTemplate>
                        <asp:RadioButton runat="server" ID="rbtnSelect" OnClick="SelectSingleRbtn(this.id)">
                        </asp:RadioButton>
                    </ItemTemplate>
                </asp:TemplateField>
                <asp:BoundField DataField="Dosage" HeaderText="Dosage" />
                <asp:BoundField DataField="Drug" HeaderText="Drug" />
                <asp:BoundField DataField="Patient" HeaderText="Patient" />
                <asp:BoundField DataField="Date" HeaderText="Date" />
             </Columns>
            </asp:GridView>

Step - 2 In the cs to bind the grid view write the below code.
              protected void Page_Load(object sender, EventArgs e)
             {
                     if (!IsPostBack)
                    {
                         Bind();
                    }
             }

             private void Bind()
            {
                 grdDisply.DataSource = GetTable();
                 grdDisply.DataBind();
            }

           static DataTable GetTable()
          {      
                DataTable table = new DataTable();
                table.Columns.Add("Dosage", typeof(int));
                table.Columns.Add("Drug", typeof(string));
                table.Columns.Add("Patient", typeof(string));
                table.Columns.Add("Date", typeof(DateTime));
                table.Rows.Add(10, "A", "Rabi", DateTime.Now);
                table.Rows.Add(20, "B", "Bopara", DateTime.Now);
                table.Rows.Add(30, "C", "Johny", DateTime.Now);
                table.Rows.Add(40, "D", "Marry", DateTime.Now);
                table.Rows.Add(50, "E", "Shetty", DateTime.Now);      
                return table;
          }        

Step - 3  In the head section of the add the below javascript code.
              <script language="javascript" type="text/javascript">
              function SelectSingleRbtn(rdbtnid) {
                  var rdBtn = document.getElementById(rdbtnid);
                  var rdBtnList = document.getElementsByTagName("input");
                  for (i = 0; i < rdBtnList.length; i++) {
                        if (rdBtnList[i].type == "radio" && rdBtnList[i].id != rdBtn.id) {
                            rdBtnList[i].checked = false;
                        }
                 }
            }
           </script>

Step - 4 Then press F5 to build and run your application.