PostgresException: 42883: operator does not exist: @ character varying

Question

im trying to make a reservation page in razor pages c#. If i make a reservation it will also appear on the page for the user. I made a button next to every reservation so you can delete the reservation. The reservation shows on the page only the date and the location. When I try to delete it from the page i get this error: PostgresException: 42883: operator does not exist: @ character varying And have no idea why. Here is the c# side:

public void OnPostRemove(ReservationModel reservation)
{
    DateTime convdayid = Convert.ToDateTime(reservation.Dayid);
    DeleteReservation(convdayid, reservation.Locationid);
}

public void DeleteReservation(DateTime convdayid, string Locationid)
{
    
    var cs = Database.Database.Connector();
    using var con = new NpgsqlConnection(cs);
    con.Open();

    var sql = "DELETE FROM reservation WHERE locationid = @Locationid AND dayid = @convdayid;";
    using var cmd = new NpgsqlCommand(sql, con);
    cmd.Parameters.AddWithValue("locationnid", Locationid);
    cmd.Parameters.AddWithValue("dayid", convdayid);
    cmd.Prepare();
    cmd.ExecuteNonQuery();

}

And this is the html side if necessary

@foreach(var reservations in @Model.ShowReservation())
{
    <form method="post">
        <fieldset>
            <div class="form-group">
                <tr>
                    <img class="img-fluid" src="/Images/Reservation.png"/>
                    <td>
                        @Html.DisplayFor(m => reservations.Dayid)
                        <input type="hidden" name="Dayid" value="@Html.DisplayFor(m => reservations.Dayid)"/>
                    </td>
                    <td>
                        @Html.DisplayFor(m => reservations.Locationid)
                        <input type="hidden" name="Locationid" value="@Html.DisplayFor(m => reservations.Locationid)"/>
                    </td>
                </tr>
                <button type="submit" value="Submit" asp-page-handler="Remove" class="btn btn-dark btn-sm">X</button>
            </div>
        </fieldset>
    </form>
    <hr>
}
<hr>

---

Edit :

The error got solved, but for some reason the specific row doesnt get deleted from the database. Nothing happens. This is what I changed about my code.

public void OnPostRemove(ReservationModel reservation)
        {
            DateTime convdayid = Convert.ToDateTime(reservation.Dayid);
            DeleteReservation(convdayid, reservation.Locationid);
        }

        public void DeleteReservation(DateTime convdayid, string Locationid)
        {
            
            var cs = Database.Database.Connector();
            using var con = new NpgsqlConnection(cs);
            con.Open();

            var sql = "DELETE FROM reservation WHERE locationid = @locationid AND dayid = @dayid;";
            using var cmd = new NpgsqlCommand(sql, con);
            cmd.Parameters.AddWithValue("locationid", Locationid);
            cmd.Parameters.AddWithValue("dayid", convdayid);
            cmd.Prepare();
            cmd.ExecuteNonQuery();

        }

Answer 1

Its trying to parse the '@' as '=@'

DELETE FROM reservation WHERE locationid = @Locationid AND dayid = @convdayid;

Is literally being passed to the Db. You need to build that string so @LocationID and @convdaid are populated accordingly. Something like:

DELETE FROM reservation WHERE locationid = 34 AND dayid = 55;