The parameterized query ..... expects the parameter '@units', which was not supplied

Question

I'm getting this exception:

The parameterized query '(@Name nvarchar(8),@type nvarchar(8),@units nvarchar(4000),@rang' expects the parameter '@units', which was not supplied.

My code for inserting is:

public int insertType(string name, string type, string units = "N\\A", string range = "N\\A", string scale = "N\\A", string description = "N\\A", Guid guid = new Guid())
{
    using (SqlConnection connection = new SqlConnection(connectionString))
    {
        connection.Open();
        SqlCommand command = new SqlCommand();
        command.CommandText = "INSERT INTO Type(name, type, units, range, scale, description, guid) OUTPUT INSERTED.ID VALUES (@Name, @type, @units, @range, @scale, @description, @guid) ";
        command.Connection = connection;
        command.Parameters.AddWithValue("@Name", name);
        command.Parameters.AddWithValue("@type", type);
        command.Parameters.AddWithValue("@units", units);
        command.Parameters.AddWithValue("@range", range);
        command.Parameters.AddWithValue("@scale", scale);
        command.Parameters.AddWithValue("@description", description);
        command.Parameters.AddWithValue("@guid", guid);
        return (int)command.ExecuteScalar();
    }
}

The exception was a surprise because I'm using the AddWithValue function and making sure I added a default parameters for the function.

Answer 1

Try this code:

SqlParameter unitsParam = command.Parameters.AddWithValue("@units", units);
if (units == null)
{
    unitsParam.Value = DBNull.Value;
}

And you must check all other parameters for null value. If it null you must pass DBNull.Value value.

Answer 2

Here's a way using the null-coalescing operator:

cmd.Parameters.AddWithValue("@units", units ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@range", range ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@scale", scale ?? (object)DBNull.Value);
cmd.Parameters.AddWithValue("@description", description ?? (object)DBNull.Value);

Or for more strict type checking:

cmd.Parameters.Add("@units", SqlDbType.Int).Value = units ?? (object)DBNull.Value;
cmd.Parameters.Add("@range", SqlDbType.Int).Value = range ?? (object)DBNull.Value;
cmd.Parameters.Add("@scale", SqlDbType.Int).Value = scale ?? (object)DBNull.Value;
cmd.Parameters.Add("@description", SqlDbType.VarChar).Value = description ?? (object)DBNull.Value;

The operator also be chained:

int?[] a = { null, null, 1 };
Console.WriteLine(a[0] ?? a[1] ?? a[2]);

Answer 3

This extension class was useful to me a couple of times so far, for those issues:

public static class DbValueExtensions
{
    // Used to convert values coming from the db
    public static T As<T>(this object source)
    {
        return source == null || source == DBNull.Value
            ? default(T)
            : (T)source;
    }

    // Used to convert values going to the db
    public static object AsDbValue(this object source)
    {
        return source ?? DBNull.Value;
    }
}

You would normally use it in two scenarios. First, when creating parameters for your query:

var parameters = new Dictionary<string, object>
{
    { "@username", username.AsDbValue() },
    { "@password", password.AsDbValue() },
    { "@birthDate", birthDate.AsDbValue() },
};

or when parsing the SqlReader values:

while (reader.Read())
{
    yield return new UserInfo(
        reader["username"].As<string>(),
        reader["birthDate"].As<DateTime>(),
        reader["graduationDate"].As<DateTime?>(),
        reader["nickname"].As<string>()
    );
}

Answer 4

command.Parameters.AddWithValue("@Name", (name == null ? "" : name));

Answer 5

This is a method to be reused with multiple parameters:

public void NullorEmptyParameter(QC.SqlCommand command, string at, string value)
{
    if (String.IsNullOrEmpty(value))
    {
        command.Parameters.AddWithValue(at, DBNull.Value);
    }
    else
        command.Parameters.AddWithValue(at, value);
}

And then you can reuse it for as many commands and params:

NullorEmptyParameter(command, "@Idea_ID", Idea_ID);
NullorEmptyParameter(command, "@Opportunities_or_Idea", Opportunities_or_Idea);

Answer 6

_{Migrating OP's solution from the question to an answer:}

The problem was that the some parameters were empty Strings (that override the default)

This is the working code:

public int insertType(string name, string type, string units = "N\\A", string range = "N\\A", string scale = "N\\A", string description = "N\\A", Guid guid = new Guid())
   {
       using (SqlConnection connection = new SqlConnection(connectionString))
       {
           connection.Open();
           SqlCommand command = new SqlCommand();
           command.CommandText = "INSERT INTO Type(name, type, units, range, scale, description, guid) OUTPUT INSERTED.ID VALUES (@Name, @type, @units, @range, @scale, @description, @guid) ";
           command.Connection = connection;
           command.Parameters.AddWithValue("@Name", name);
           command.Parameters.AddWithValue("@type", type);

           if (String.IsNullOrEmpty(units))
           {
               command.Parameters.AddWithValue("@units", DBNull.Value); 
           }
           else
               command.Parameters.AddWithValue("@units", units);
           if (String.IsNullOrEmpty(range))
           {
               command.Parameters.AddWithValue("@range", DBNull.Value);
           }
           else
               command.Parameters.AddWithValue("@range", range);
           if (String.IsNullOrEmpty(scale))
           {
               command.Parameters.AddWithValue("@scale", DBNull.Value);
           }
           else
               command.Parameters.AddWithValue("@scale", scale);
           if (String.IsNullOrEmpty(description))
           {
               command.Parameters.AddWithValue("@description", DBNull.Value);
           }
           else
               command.Parameters.AddWithValue("@description", description);
                    
           command.Parameters.AddWithValue("@guid", guid);

           return (int)command.ExecuteScalar();
       }
   }