Exception when AddWithValue parameter is NULL

Question

I have following code for specifying parameters for SQL query. I am getting following exception when I use Code 1; but works fine when I use Code 2. In Code 2 we have a check for null and hence a if..else block.

Exception:

The parameterized query '(@application_ex_id nvarchar(4000))SELECT E.application_ex_id A' expects the parameter '@application_ex_id', which was not supplied.

Code 1:

command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);

Code 2:

if (logSearch.LogID != null)
{
         command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
}
else
{
        command.Parameters.AddWithValue("@application_ex_id", DBNull.Value );
}

QUESTION

1. Can you please explain why it is unable to take NULL from logSearch.LogID value in Code 1 (but able to accept DBNull)?

2. Is there a better code to handle this?

Reference:

1. Assign null to a SqlParameter
2. Datatype returned varies based on data in table
3. Conversion error from database smallint into C# nullable int
4. What is the point of DBNull?

CODE

    public Collection<Log> GetLogs(LogSearch logSearch)
    {
        Collection<Log> logs = new Collection<Log>();

        using (SqlConnection connection = new SqlConnection(connectionString))
        {
            connection.Open();

            string commandText = @"SELECT  *
                FROM Application_Ex E 
                WHERE  (E.application_ex_id = @application_ex_id OR @application_ex_id IS NULL)";

            using (SqlCommand command = new SqlCommand(commandText, connection))
            {
                command.CommandType = System.Data.CommandType.Text;

                //Parameter value setting
                //command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
                if (logSearch.LogID != null)
                {
                    command.Parameters.AddWithValue("@application_ex_id", logSearch.LogID);
                }
                else
                {
                    command.Parameters.AddWithValue("@application_ex_id", DBNull.Value );
                }

                using (SqlDataReader reader = command.ExecuteReader())
                {
                    if (reader.HasRows)
                    {
                        Collection<Object> entityList = new Collection<Object>();
                        entityList.Add(new Log());

                        ArrayList records = EntityDataMappingHelper.SelectRecords(entityList, reader);

                        for (int i = 0; i < records.Count; i++)
                        {
                            Log log = new Log();
                            Dictionary<string, object> currentRecord = (Dictionary<string, object>)records[i];
                            EntityDataMappingHelper.FillEntityFromRecord(log, currentRecord);
                            logs.Add(log);
                        }
                    }

                    //reader.Close();
                }
            }
        }

        return logs;
    }

Answer 1

Annoying, isn't it.

You can use:

command.Parameters.AddWithValue("@application_ex_id",
       ((object)logSearch.LogID) ?? DBNull.Value);

Or alternatively, use a tool like "dapper", which will do all that messing for you.

For example:

var data = conn.Query<SomeType>(commandText,
      new { application_ex_id = logSearch.LogID }).ToList();

I'm tempted to add a method to dapper to get the IDataReader... not really sure yet whether it is a good idea.

Answer 2

I find it easier to just write an extension method for the SqlParameterCollection that handles null values:

public static SqlParameter AddWithNullableValue(
    this SqlParameterCollection collection,
    string parameterName,
    object value)
{
    if(value == null)
        return collection.AddWithValue(parameterName, DBNull.Value);
    else
        return collection.AddWithValue(parameterName, value);
}

Then you just call it like:

sqlCommand.Parameters.AddWithNullableValue(key, value);

Answer 3

Just in case you're doing this while calling a stored procedure: I think it's easier to read if you declare a default value on the parameter and add it only when necessary.

SQL:

DECLARE PROCEDURE myprocedure
    @myparameter [int] = NULL
AS BEGIN

C#:

int? myvalue = initMyValue();
if (myvalue.hasValue) cmd.Parameters.AddWithValue("myparamater", myvalue);

Answer 4

some problem, allowed with Necessarily set SQLDbType

command.Parameters.Add("@Name", SqlDbType.NVarChar);
command.Parameters.Value=DBNull.Value

where SqlDbType.NVarChar you type. Necessarily set SQL type.