How to fix "There is already an open DataReader ..."

Question

I am having problems trying to fix this error:

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

I know what this error means and how I should fix it, but I create a new NpgsqlCommand on an existing NpgsqlConnection each time and when the previous command is not finished yet, this error occurs.

The command is run as follows:

private object RunSelectScalar(NpgsqlCommand cmd) {
    cmd.Connection = connection;     // connection is a connected NpgsqlConnection
    object result = cmd.ExecuteScalar();

    return result;
}

object o = RunSelectScalar(new NpgsqlCommand("SELECT foo FROM bar LIMIT 1"));

so, I don't know how I could close it, or use using, as I do not assign a DataReader.

Answer 1

Add

Preload Reader = true;

with your connection string. Worked for me.

For example:

 <add name="dbTestConnectionString" connectionString="Server=localhost;Database=dbNew3;User Id=postgres;Password=your_pass;Preload Reader = true;" providerName="Npgsql" />