sub read_file {
  @_ == 2 or croak 'Incorrect number of parameters';

  my $dbh    = shift;
  my $source = shift;

  my $statement = sprintf(q{
      SELECT NodeId
           , Title
           , Date
           , LastReputation
           , Reputation
        FROM %s
    },
    $source,
  );

  my $sth = $dbh->prepare($statement);
  $sth->execute;

  my %nodehash;

  while(my $row = $sth->fetchrow_hashref) {
    croak "Node ID $row->{NodeId} is duplicated!"
      if exists $nodehash{ $row->{NodeId} };

    $nodehash{ $row->{NodeId} } = $row;
  }

  return \%nodehash;
}