Invalid attempt to call FieldCount when reader is closed

Question

The error above occurs when I try to do a dataReader.Read on the data recieved from the database. I know there are two rows in there so it isnt because no data actually exists.

Could it be the CommandBehavior.CloseConnection, causing the problem? I was told you had to do this right after a ExecuteReader? Is this correct?

        try
        {
            _connection.Open();
            using (_connection)
            {
                SqlCommand command = new SqlCommand("SELECT * FROM Structure", _connection);
                SqlDataReader dataReader = command.ExecuteReader(CommandBehavior.CloseConnection);

                if (dataReader == null) return null;

                var newData = new List<Structure>();
                while (dataReader.Read())
                {
                    var entity = new Structure
                    {
                        Id = (int)dataReader["StructureID"],
                        Path = (string)dataReader["Path"],
                        PathLevel = (string)dataReader["PathLevel"],
                        Description = (string)dataReader["Description"]
                    };

                    newData.Add(entity);
                }
                dataReader.Close();

                return newData;
            }
        }
        catch (SqlException ex)
        {
            AddError(new ErrorModel("An SqlException error has occured whilst trying to return descendants", ErrorHelper.ErrorTypes.Critical, ex));
            return null;
        }
        catch (Exception ex)
        {
            AddError(new ErrorModel("An error has occured whilst trying to return descendants", ErrorHelper.ErrorTypes.Critical, ex));
            return null;
        }
        finally
        {
            _connection.Close();
        }
    }

Thanks in advance for any help.

Clare

score 3 · Answer 1 · answered Apr 15 '14 at 14:04

3

When you use the Using in C#, after the last } from the using, the Connection automatically close, thats why you get the fieldcount to be closed when u try to read him, as that is impossible, because u want those datas, read then before close the using, or u can open and close manually the connection, by not using the (using)

answered Apr 15 '14 at 14:04

user2442328

31
1

Agreed. The " using (_connection) {" is what is closing the datareader before you "consume" the datareader. Take out the "using" and keep the " CommandBehavior.CloseConnection "...and after you consume the datareader, make sure you call .Close() on it. – granadaCoder Apr 25 '14 at 14:58

score 2 · Accepted Answer · answered Aug 12 '10 at 15:41

Your code, as displayed is fine. I've taken it into a test project, and it works. It's not immediately clear why you get this message with the code shown above. Here are some debugging tips/suggestions. I hope they're valuable for you.

Create a breakpoint on the while (dataReader.Read()). Before it enters its codeblock, enter this in your Immediate or Watch Window: dataReader.HasRows. That should evaluate to true.
While stopped on that Read(), open your Locals window to inspect all the properties of dataReader. Ensure that the FieldCount is what you expect from your SELECT statement.
When stepping into this Read() iteration, does a student object get created at all? What's the value of dataReader["StructureID"] and all others in the Immediate Window?

It's not the CommandBehavior.CloseConnection causing the problem. That simply tells the connection to also close itself when you close the datareader.

You were right it wasn't the CommandBehavior.CloseConnection causing the issue. This masked the real issue - trying to convert a a datatype to thewrong thing. 'Invalid attempt to call FieldCount when reader is closed' only occurred when I stepped through my code (maybe because I took to long?) — ClareBear, Aug 13 '10 at 09:18
Yes..this was the datatype issue..The datatype in the database were datetime2 and in the source code i was referring this field as string.. So i had to type cast the datetime2 field in the database to varchar(11) before getting. — Krishna, Jun 21 '19 at 19:14

score 1 · Answer 3 · answered Jun 12 '14 at 09:35

When I got that error, it happened to be a command timeout problem (I was reading some large binary data). As a first attempt, I increased the command timeout (not the connection timeout!) and the problem was solved. Note: while attempting to find out the problem, I tried to listen to the (Sql)connection's StateChanged event, but it turned out that the connection never fall in a "broken" state.

score 1 · Answer 4 · answered Feb 23 '19 at 21:26

Same problem here. Tested all the above solutions

increase command timeout
close the connection after read

Here's the code

    1 objCmd.Connection.Open()
    2 objCmd.CommandTimeout = 3000
    3 Dim objReader As OleDbDataReader = objCmd.ExecuteReader()
    4 repeater.DataSource = objReader
    5 CType(repeater, Control).DataBind()
    6 objReader.Close()
    7 objCmd.Connection.Dispose()

Moreover, at line 4 objReader has Closed = False

score 0 · Answer 5 · answered Feb 14 '20 at 18:00

I got this exception while using the VS.NET debugger and trying to examine some IQueryable results. Bad decision because the IQueryable resulted in a large table scan. Stopping and restarting the debugger and NOT trying to preview this particular IQueryable was the workaround.

Invalid attempt to call FieldCount when reader is closed

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