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    __assert_explain($explain_sth->fetchall_arrayref( +{} ), $statement);
}

sub __assert_explain {
    my($explains, $statement) = @_;
    my $clean_statement = __clean_statement($statement);
    my @using_no_key = grep {__should_alert($_) } @$explains;
    return unless @using_no_key;

    __warn->('[explain alert] ', $clean_statement);
}

sub __should_alert {
    my ( $explain_by_table ) = @_;
    my $extra = $explain_by_table->{Extra};
    my $type  = $explain_by_table->{type};
    my $possible_key   = $explain_by_table->{possible_keys};
    # search uniq/primary key but not found any rows
    return 0 if $extra and $extra =~ m/^Impossible/;
    # not using any index
    return 0 if defined $possible_key;
    return 1 if $type and $type eq 'ALL';
    return 0;
}

sub __clean_statement {
    my $statement = shift;
    $statement =~ s/\n/ /g;
    $statement =~ s/\s+/ /g;
    return $statement;
}

sub __warn {
    my($message, $statement, $using_no_key) = @_;

    if (ref $OUTPUT eq 'CODE') {
        $OUTPUT->(
            message      => $message,
            statement    => $statement,
            using_no_key => $using_no_key,
        );
    } else {
        print {$OUTPUT} $message, ' statement:', $statement;
    }
}

1;
__END__

=head1 NAME

DBIx::AssertIndex - show error when SQL query doesn't use index.

=head1 SYNOPSIS

  use DBIx::AssertIndex;
  my $row = $dbh->selectrow_hashref(q{SELECT * FROM some_table WHERE no_indexed_column = 'foo'});

  or

  > starman -MDBIx::AssertIndex app.psgi

=head1 DESCRIPTION

DBIx::AssertIndex is run explain with SELECT SQL and detect query without any index.

Works only DBD::mysql.

=head1 AUTHOR

daichi hiroki E<lt>daichi.hiroki@mixi.co.jpE<gt>

=head1 SEE ALSO

=head1 LICENSE

This library is free software; you can redistribute it and/or modify
it under the same terms as Perl itself.

=cut