SQLException The parameterized query ### which was not supplied

Question

I've searched this site, and other sites to understand and get rid of this exception. Many answers, but I can't find where "I'm wrong". This i the exception:

The parameterized query '(@listenr int,@stregko nvarchar(4000))SELECT * FROM Indkøbsliste' expects the parameter '@stregko', which was not supplied.

And here i my code.

    public Indkøbsliste findIndkøbslisteStregkode(string stregko, int listenr)
    {
        Indkøbsliste inl = new Indkøbsliste();



        SqlConnection myCon = DBcon.getInstance().conn();
        myCon.Open();

        string query = "SELECT * FROM Indkøbsliste WHERE Stregkode = @stregko AND ListeNr = @listenr";
        SqlCommand com = new SqlCommand(query, myCon);
        com.Parameters.Add("@stregko", System.Data.SqlDbType.VarChar).Value = stregko; 
        com.Parameters.Add("@listenr", System.Data.SqlDbType.Int).Value = listenr; 
        SqlDataReader dr = com.ExecuteReader();
        if (dr.Read())
        {

            inl.ListeNr = dr.GetInt32(1);
            inl.Stregkode = dr.GetString(2);
            inl.Navn = dr.GetString(3);
            inl.Antal = dr.GetInt32(4);
            inl.Pris = dr.GetDecimal(5);

        }
        myCon.Close();
        return inl;
    }

Answer 1

Make use of AddWithValue method

com.Parameters.AddWithValue("@stregko", stregko);
or 
com.Parameters.Add("@stregko", SqlDbType.NVarChar, 50).Value = stregko;
or 
SqlParameter parameter = new SqlParameter("@stregko", SqlDbType.NVarChar, 50);
parameter.Value = stregko;
com.Parameters.Add(parameter);

rather than

com.Parameters.Add("@stregko", System.Data.SqlDbType.VarChar).Value = stregko;

Answer 2

The SQL query expects a unicode string for stregko but you provide a non-unicode string.

Try to change your c# code for assigning the parameter as follows:

com.Parameters.Add("@stregko", System.Data.SqlDbType.NVarChar).Value = stregko; 

Note the "N" in NVarChar!

Answer 3

您的SQL参数是nvarchar尝试在C＃代码中使用System.Data.SqlDbType.NVarChar 。

Answer 4

as from your error message, try to change:

com.Parameters.Add("@stregko", System.Data.SqlDbType.VarChar)

with

com.Parameters.Add("@stregko", System.Data.SqlDbType.NVarChar)

Answer 5

您需要指定大小。

com.Parameters.Add("@stregko", System.Data.SqlDbType.NVarChar,50).Value = stregko;