mysql The transaction associated with this command is not the connection’s active transaction

Code Fix: Set MySqlCommand.Transaction

ADO.NET example

using (var connection = new MySqlConnection(...))
{
    connection.Open();
    using (var transaction = connection.BeginTransaction())
    using (var command = connection.CreateCommand())
    {
        command.CommandText = "SELECT ...";

        // *** ADD THIS LINE ***
        command.Transaction = transaction;

        // otherwise, this will throw System.InvalidOperationException: The transaction associated with this command is not the connection's active transaction.
        command.ExecuteScalar();
    }
}

Dapper Example

using (var connection = new MySqlConnection(...))
{
    connection.Open();
    using (var transaction = connection.BeginTransaction())
    {
        // this will throw System.InvalidOperationException: The transaction associated with this command is not the connection's active transaction.
        connection.Query("SELECT ...");

        // use this instead:
        connection.Query("SELECT ...", transaction: transaction);
    }
}