DataReader already open

Question

I got a problem with an error that say that my datareader is already open.

My code looks like this

public static Users GetByID(int ID, SqlConnection connection)
    {
        SqlCommand command = new SqlCommand("Select Name, Email, LastLogin, FK_Role_ID from Users where ID=@id");
        command.Connection = connection;

        command.Parameters.Add(new SqlParameter("id", ID));

        SqlDataReader reader = command.ExecuteReader();
        if (reader.Read())
        {
            Users user = new Users();
            user.ID = ID;
            user.Name = reader.GetString(0);
            user.Email = reader.GetString(1);
            user.LastLogin = reader.GetString(2);
            user.role = Role.GetRoleByID(reader.GetInt32(3), connection);
            reader.Close();
            return user;
        }
        else
        {
            reader.Close();
            return null;
        }
    }

The error occours in the Role.GetRoleByID saying that the datareader command is alreader open. Which is true, but how do I call Role.GetRoleByID with the information from my reader.

I code in c# and ASP.NET

Answer 1

It looks like your Role.GetRoleByID will try to reuse the connection.

Options:

• Fetch the data you need from the SqlDataReader within GetByID , close that reader, and then call Role.GetRoleByID (so you've only got one active reader at a time)
• Enable Multiple Active ResultSets (MARS) - I can't say I have any experience of that
• Make each method use a separate connection to reduce the dependencies between the methods. Note that the connection pool will make the opening/closing reasonably cheap.

I'd go with the first option if I were you - or possibly the last. I'd also use a using statement to close the reader automatically:

private const string GetUserByIdSql =
    "Select Name, Email, LastLogin, FK_Role_ID from Users where ID=@id";

public static Users GetByID(int ID, SqlConnection connection)
{
    var sql = ;
    Users user;
    int roleId;
    using (var command = new SqlCommand(GetUserByIdSql, connection))
    {
        command.Parameters.Add(new SqlParameter("id", ID));
        using (var reader = command.ExecuteReader())
        {
            if (!reader.Read())
            {
                return null;
            }
            user = new Users
            {
                Name = reader.GetString(0),
                Email = reader.GetString(1),
                LastLogin = reader.GetString(2),
            };
            // Remember this so we can call GetRoleByID after closing the reader
            roleID = reader.GetInt32(3);
        }
    }
    user.Role = Role.GetRoleByID(roleID, connection);
    return user;
}

As a fourth option - why not just perform the join required by GetRoleByID in your existing query? That would mean you'd only need one trip to the database.

Answer 2

You may consider using a Select query with requisite join, to be able to receive Role from the same query.

Also, it is recommended to use (using reader = command.ExecuteReader() ) , so that the reader is closed and Disposed as soon as the scope is over.

Answer 3

您是否允许MARS您的连接字符串（ MultipleActiveResultSets=true ）？