Grid view edit - drop down list issue - asp.net

Question

I have a grid view and i'm trying to create a drop down list in the edit mode of the grid view.
The grid view show the users in my project and i want the drop down list let them change their city from the cities table in my database.
I have tried to do using a Template editing according to a video i saw on youtube(https://www.youtube.com/watch?v=YB2pe_C2Tbg&t=191s&ab_channel=MukeshChaudhary). Although, i'm getting the error:
System.Data.OleDb.OleDbException: 'You cannot add or change a record
because a related record is required in table 'cities'.'
Code behind
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using RapidTyper.App_Code;
public partial class ManagerChange : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if(!Page.IsPostBack) PopulateGrid();
}
private DataSet GetData()
{
UserService UserService = new UserService();
return UserService.GetUsers();
}
private void PopulateGrid()
{
GridView1.DataSource = GetData();
GridView1.DataBind();
}
protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
GridView1.EditIndex = e.NewEditIndex;
PopulateGrid();
}
protected void GridView1_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)
{
GridView1.EditIndex = -1;
PopulateGrid();
}
protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
User userDetaling = new User();
userDetaling.setFName(((TextBox)GridView1.Rows[e.RowIndex].Cells[0].Controls[0]).Text);
userDetaling.setLName(((TextBox)GridView1.Rows[e.RowIndex].Cells[1].Controls[0]).Text);
userDetaling.setID(GridView1.Rows[e.RowIndex].Cells[2].Text);
userDetaling.setBirthDate(((TextBox)GridView1.Rows[e.RowIndex].Cells[3].Controls[0]).Text);
userDetaling.setAddress(((TextBox)GridView1.Rows[e.RowIndex].Cells[5].Controls[0]).Text);
userDetaling.setZipCode (((TextBox)GridView1.Rows[e.RowIndex].Cells[6].Controls[0]).Text);
userDetaling.setEmail(((TextBox)GridView1.Rows[e.RowIndex].Cells[7].Controls[0]).Text);
userDetaling.setPassword(((TextBox)GridView1.Rows[e.RowIndex].Cells[8].Controls[0]).Text);
UserService UserService = new UserService();
UserService.UpdateUser(userDetaling);
GridView1.EditIndex = -1;
PopulateGrid();
}
}
Aspx
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" BackColor="#DEBA84" BorderColor="#DEBA84" BorderStyle="None" BorderWidth="1px" CellPadding="3" CellSpacing="2" OnRowCancelingEdit="GridView1_RowCancelingEdit" OnRowEditing="GridView1_RowEditing" OnRowUpdating="GridView1_RowUpdating" style="margin-top: 21px">
<Columns>
<asp:BoundField DataField="fName" HeaderText="Name" />
<asp:BoundField DataField="lName" HeaderText="Last Name" />
<asp:BoundField DataField="ID" HeaderText="ID" ReadOnly="True" />
<asp:BoundField DataField="birthDate" HeaderText="Birth Date" />
<asp:TemplateField HeaderText="city">
<EditItemTemplate>
<asp:DropDownList ID="DropDownList1" runat="server" DataSourceID="SqlDataSource1" DataTextField="cityName" DataValueField="cityNum">
</asp:DropDownList>
<asp:SqlDataSource ID="SqlDataSource1" runat="server" ConnectionString="<%$ ConnectionStrings:ConnectionString %>" ProviderName="<%$ ConnectionStrings:ConnectionString.ProviderName %>" SelectCommand="SELECT * FROM [cities]"></asp:SqlDataSource>
</EditItemTemplate>
<ItemTemplate>
<asp:Label ID="Label1" runat="server" Text='<%# Bind("cityName") %>'></asp:Label>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="address" HeaderText="address" />
<asp:BoundField DataField="zipcode" HeaderText="zip code" />
<asp:BoundField DataField="email" HeaderText="email" />
<asp:BoundField DataField="userPassword" HeaderText="password" />
<asp:CommandField ButtonType="Button" HeaderText="Edit" ShowEditButton="True" />
</Columns>
<FooterStyle BackColor="#F7DFB5" ForeColor="#8C4510" />
<HeaderStyle BackColor="#A55129" Font-Bold="True" ForeColor="White" />
<PagerStyle ForeColor="#8C4510" HorizontalAlign="Center" />
<RowStyle BackColor="#FFF7E7" ForeColor="#8C4510" />
<SelectedRowStyle BackColor="#738A9C" Font-Bold="True" ForeColor="White" />
<SortedAscendingCellStyle BackColor="#FFF1D4" />
<SortedAscendingHeaderStyle BackColor="#B95C30" />
<SortedDescendingCellStyle BackColor="#F1E5CE" />
<SortedDescendingHeaderStyle BackColor="#93451F" />
</asp:GridView>