Error converting nvarchar to int in ExecuteNonQuery - asp.net

Question

I am getting an error for the following program in asp.net.
I have checked sql and name is in nvarchar.
{
con.Open();
SqlCommand cmd = new SqlCommand("bookinsertion2", con);
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("#idnumber",txtid.Text);
cmd.Parameters.AddWithValue("#name", txtname.Text);
cmd.Parameters.AddWithValue("#year", txtyear.Text);
cmd.Parameters.AddWithValue("#department", txtdepart.Text);
cmd.Parameters.AddWithValue("#bookname", ddlbookavail.SelectedItem.ToString());
cmd.ExecuteNonQuery();
con.Close();
Response.Redirect("~/LendingForm2.aspx");
}
This is the code of the stored procedure
create Procedure [dbo].[bookinsertion2]
#idnumber int,
#name nvarchar(20),
#year int,
#department nvarchar(30),
#bookname nvarchar(25)
as
Begin
insert into tbllendinginfo values(#idnumber,#name,#year,#department,#bookname)
insert into tbllendinginfo(Dateofbooktaken) values(GETDATE())
update tblbookinfo set BooksAvailable=BooksAvailable-(select COUNT(Id) from tbllendinginfo where BookName=#bookname) where Name=#bookname
end
The error is " Conversion failed when converting the nvarchar value 'Mike' to data type int. "

Answer 1

The error message is clear, one or more of the parameters expected by the stored procedure are not of type nvarchar. Probably the #year and #idnumber parameters are an integers. If that's true then you need to call
cmd.Parameters.AddWithValue("#idnumber",Convert.ToInt32(txtid.Text));
cmd.Parameters.AddWithValue("#year", Convert.ToInt32(txtyear.Text));
Said that, please try, if possible to avoid the call to AddWithValue, in particular in case where strings or date are involved. AddWithValue determines the type of the parameter from the input value and most of the time is correct, but there are situations where it decides for a wrong datatype and the errors are difficult to find. Moreover AddWithValue with strings is a performance hurdle.
A better explanation could be found in these two articles.
Can we stop using AddWithValue() already?
How Data Access Code Affects Database Performance
You could rewrite the code above using the Object Initializer Syntax
{
con.Open();
SqlCommand cmd = new SqlCommand("bookinsertion2", con);
cmd.CommandType = System.Data.CommandType.StoredProcedure;
cmd.Parameters.Add(
new SqlParameter
{
ParameterName = "#idnumber",
SqlDbType = SqlDbType.Int,
Value = Convert.ToInt32(txtid.Text)
});
cmd.Parameters.Add(
new SqlParameter
{
ParameterName = "#name",
SqlDbType = SqlDbType.NVarChar,
Size = 50,
Value = txtname.Text
});
cmd.Parameters.Add(
new SqlParameter
{
ParameterName = "#year",
SqlDbType = SqlDbType.Int,
Value = Convert.ToInt32(txtyear.Text)
});
cmd.Parameters.Add(
new SqlParameter
{
ParameterName = "#department",
SqlDbType = SqlDbType.NVarChar,
Size = 50,
Value = txtdepart.Text
});
cmd.Parameters.Add(
new SqlParameter
{
ParameterName = "#bookname",
SqlDbType = SqlDbType.NVarChar,
Size = 50,
Value = ddlbookavail.SelectedItem.ToString()
});
cmd.ExecuteNonQuery();
con.Close();
Response.Redirect("~/LendingForm2.aspx");
}
EDIT
After your edit I think the problem is in this line of the stored procedure:
insert into tbllendinginfo values(#idnumber,#name,#year,#department,#bookname)
You haven't specified the columns' names but just the parameters. So the server inserts the parameter following the order of definition of the columns in the datatable.
Of course, if the second column in the table is not the column that should receive the #name parameter you could have serious problems.
You could fix the problem listing the name of the columns in the same order iun which you put the parameter inside the VALUES clause or changing the order of the parameters to follow the order of the column names.
For example (I don't know the column names so you should fix them)
insert into tbllendinginfo (idnumber, name, bookyear, department, bookname)
values(#idnumber,#name,#year,#department,#bookname)