How do I cleanly extract MySQL enum values in Perl? - mysql

Question

I have some code which needs to ensure some data is in a mysql enum prior to insertion in the database. The cleanest way I've found of doing this is the following code:
sub enum_values {
my ( $self, $schema, $table, $column ) = #_;
# don't eval to let the error bubble up
my $columns = $schema->storage->dbh->selectrow_hashref(
"SHOW COLUMNS FROM `$table` like ?",
{},
$column
);
unless ($columns) {
X::Internal::Database::UnknownColumn->throw(
column => $column,
table => $table,
);
}
my $type = $columns->{Type} or X::Panic->throw(
details => "Could not determine type for $table.$column",
);
unless ( $type =~ /\Aenum\((.*)\)\z/ ) {
X::Internal::Database::IncorrectTypeForColumn->throw(
type_wanted => 'enum',
type_found => $type,
);
}
$type = $1;
require Text::CSV_XS;
my $csv = Text::CSV_XS->new;
$csv->parse($type) or X::Panic->throw(
details => "Could not parse enum CSV data: ".$csv->error_input,
);
return map { /\A'(.*)'\z/; $1 }$csv->fields;
}
We're using DBIx::Class. Surely there is a better way of accomplishing this? (Note that the $table variable is coming from our code, not from any external source. Thus, no security issue).

Answer 1

No need to be so heroic. Using a reasonably modern version of DBD::mysql, the hash returned by DBI's column info method contains a pre-split version of the valid enum values in the key mysql_values:
my $sth = $dbh->column_info(undef, undef, 'mytable', '%');
foreach my $col_info ($sth->fetchrow_hashref)
{
if($col_info->{'TYPE_NAME'} eq 'ENUM')
{
# The mysql_values key contains a reference to an array of valid enum values
print "Valid enum values for $col_info->{'COLUMN_NAME'}: ",
join(', ', #{$col_info->{'mysql_values'}}), "\n";
}
...
}

Answer 2

I'd say using Text::CSV_XS may be an overkill, unless you have weird things like commas in enums (a bad idea anyway if you ask me). I'd probably use this instead.
my #fields = $type =~ / ' ([^']+) ' (?:,|\z) /msgx;
Other than that, I don't think there are shortcuts.

Answer 3

I spent part of the day asking the #dbix-class channel over on MagNet the same question and came across this lack of answer. Since I found the answer and nobody else seems to have done so yet, I'll paste the transcript below the TL;DR here:
my $cfg = new Config::Simple( $rc_file );
my $mysql = $cfg->get_block('mysql');
my $dsn =
"DBI:mysql:database=$mysql->{database};".
"host=$mysql->{hostname};port=$mysql->{port}";
my $schema =
DTSS::CDN::Schema->connect( $dsn, $mysql->{user}, $mysql->{password} );
my $valid_enum_values =
$schema->source('Cdnurl')->column_info('scheme')->{extra}->{list};
And now the IRC log of me beating my head against a wall:
14:40 < cj> is there a cross-platform way to get the valid values of an
enum?
15:11 < cj> it looks like I could add 'InflateColumn::Object::Enum' to the
__PACKAGE__->load_components(...) list for tables with enum
columns
15:12 < cj> and then call values() on the enum column
15:13 < cj> but how do I get dbic-dump to add
'InflateColumn::Object::Enum' to
__PACKAGE__->load_components(...) for only tables with enum
columns?
15:20 < cj> I guess I could just add it for all tables, since I'm doing
the same for InflateColumn::DateTime
15:39 < cj> hurm... is there a way to get a column without making a
request to the db?
15:40 < cj> I know that we store in the DTSS::CDN::Schema::Result::Cdnurl
class all of the information that I need to know about the
scheme column before any request is issued
15:42 <#ilmari> cj: for Pg and mysql Schema::Loader will add the list of
valid values to the ->{extra}->{list} column attribute
15:43 <#ilmari> cj: if you're using some other database that has enums,
patches welcome :)
15:43 <#ilmari> or even just a link to the documentation on how to extract
the values
15:43 <#ilmari> and a willingness to test if it's not a database I have
access to
15:43 < cj> thanks, but I'm using mysql. if I were using sqlite for this
project, I'd probably oblige :-)
15:44 <#ilmari> cj: to add components to only some tables, use
result_components_map
15:44 < cj> and is there a way to get at those attributes without making a
query?
15:45 < cj> can we do $schema->resultset('Cdnurl') without having it issue
a query, for instance?
15:45 <#ilmari> $result_source->column_info('colname')->{extra}->{list}
15:45 < cj> and $result_source is $schema->resultset('Cdnurl') ?
15:45 <#ilmari> dbic never issues a query until you start retrieving the
results
15:45 < cj> oh, nice.
15:46 <#ilmari> $schema->source('Cdnurl')
15:46 <#ilmari> the result source is where the result set gets the results
from when they are needed
15:47 <#ilmari> names have meanings :)