Exception when AddWithValue parameter is NULL
C#.Netado.netC# Problem Overview
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
-
Can you please explain why it is unable to take NULL from logSearch.LogID value in Code 1 (but able to accept DBNull)?
-
Is there a better code to handle this?
Reference:
- https://stackoverflow.com/questions/4555935/how-to-assign-null-to-a-sqlparameter
- https://stackoverflow.com/questions/13306275/datatype-returned-varies-based-on-data-in-table
- https://stackoverflow.com/questions/13265704/conversion-error-from-database-smallint-into-c-sharp-nullable-int?lq=1
- https://stackoverflow.com/questions/4488727/what-is-the-point-of-dbnull/9632050#9632050
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;
}
C# Solutions
Solution 1 - C#
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.
Solution 2 - C#
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);
Solution 3 - C#
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);
Solution 4 - C#
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.