Can't figure out exception message

Question

I am having the following error message and I am using petaPOCO. Why am I having this error message and What am I doing wrong to have this message:

{"There is already an open DataReader associated with this Command which must be closed first."}

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This is what I have been able to copy for the exception message.

System.InvalidOperationException was caught Message=There is already an open DataReader associated with this Command which must be closed first. Source=System.Data StackTrace: at System.Data.SqlClient.SqlInternalConnectionTds.ValidateConnectionForExecute(SqlCommand command) at System.Data.SqlClient.SqlConnection.ValidateConnectionForExecute(String method, SqlCommand command) at System.Data.SqlClient.SqlCommand.ValidateCommand(String method, Boolean async) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method, DbAsyncResult result) at System.Data.SqlClient.SqlCommand.RunExecuteReader(CommandBehavior cmdBehavior, RunBehavior runBehavior, Boolean returnStream, String method) at System.Data.SqlClient.SqlCommand.ExecuteScalar() at PetaPoco.Database.Insert(String tableName, String primaryKeyName, Boolean autoIncrement, Object poco) in C:\Dev\Code\API\Models\PetaPoco.cs:line 1243 InnerException:

Answer 1

Here is an excellent explanation why this exception is raised:

http://blogs.msdn.com/b/spike/archive/2009/08/20/there-is-already-an-open-datareader-associated-with-this-command-which-must-be-closed-first-explained.aspx

The conclusion is as following:

Because the SqlDataReader keeps the memory stream (resultset) available until you explicitly close the SqlDataReader you can get this exception if you try to create a new reader without closing the previous one.

Alter your code to have a using statement whenever you create a SqlDataReader:

SqlCommand cmd = new SqlCommand(sql, con);
using (SqlDataReader rdr = cmd.ExecuteReader())
{
  while (rdr.Read())
  {
    Console.WriteLine("cid: {0}, ctext: {1}", rdr[0].ToString(), rdr[1].ToString());
  }
}

Using will automatically call dispose() (which closes the reader) when the closure (ending } ) is reached.

If this exception is raised in petaPOCO then there is a bug in their code or you are using the code in an unspecified way.

Answer 2

I know this is old, but I wanted to add something that may help the next person searching for this. This error happens if you use the Query method. The Query method doesn't load everything in memory. If you need to have it loaded and then have the connection closed, you need to use Fetch.

This is from the website:

Query vs Fetch

The Database class has two methods for retrieving records Query and Fetch. These are pretty much identical except Fetch returns a List<> of POCO's whereas Query uses yield return to iterate over the results without loading the whole set into memory.

Hope this helps someone else.

Answer 3

Your ORM (or your usage pattern of the ORM) expects the underlying ADO.NET provider to allow for multiple open DataReaders on a single Connection. SQL Server Provider you seem to use can do that, but you must add MultipleActiveResultSets=True to the connection string you use to connect to the database.

Answer 4

This exception can also be thrown in PetaPoco if your poco doesn't have a parameterless constructor of either public or protected visibility.