DBIx::DataModel::Doc::Cookbook - Helpful recipes
This chapter is part of the DBIx::DataModel manual.
DBIx::DataModel
SYNOPSIS AND DESCRIPTION
DESIGN
QUICKSTART
REFERENCE
MISC
INTERNALS
GLOSSARY
This chapter provides some recipes for common ORM tasks.
A schema skeleton can be produced automatically from the following external sources : a DBI connection, a SQL::Translator parser, or a DBIx::Class schema. See DBIx::DataModel::Schema::Generator.
DBI
DBIx::Class
Defining methods in any Perl class does not require to have a file corresponding to that class; it suffices to define the method within the appropriate package. So the easiest way to add methods into tables is to first let DBIx::DataModel create the schema and table classes, and then switch to those packages, all in the same file :
# define schema, tables, associations (current package doesn't matter) DBIx::DataModel->Schema('Some::Schema') ->Table(qw/Foo foo foo_id/) ->Table(...) ->Association(...) ->...; # add a method into table 'Foo' package Some::Schema::Foo; sub my_added_method { my $self = shift; ... } # go back to main package package main; ...
Another way to achieve the same result is to use DBIx::DataModel's internal utility method for injecting methods into classes :
use DBIx::DataModel::Meta::Utils; DBIx::DataModel::Meta::Utils->define_method( class => 'Some::Schema::Foo', name => 'my_added_method, body => sub {my $self = shift; ...}, );
Here is an example of inflating/deflating a scalar value from the database into a Perl object :
# declare column type use Date::Simple; $schema->Type(Date_simple => from_DB => sub {Date::Simple->new($_[0]) if $_[0] }, to_DB => sub {$_[0] = $_[0]->as_str if $_[0] }, ); # apply column type to columns My::Table1->metadm->define_column_type(Date_simple => qw/d_start d_end/); My::Table2->metadm->define_column_type(Date_simple => qw/d_birth/);
Caveat: the from_DB / to_DB functions do not apply automatically within -where conditions. So the following would not work :
from_DB
to_DB
-where
use Date::Simple qw/today/; my $rows = $schema->table($name)->select( -where => {d_end => {'<' => today()}}, );
because today() returns a Date::Simple object that will not be understood by SQL::Abstract when generating the SQL query. DBIx::DataModel is not clever enough to inspect the -where conditions and decide which column types to apply, so you have to do it yourself :
today()
Date::Simple
my $today = today()->as_str; my $rows = $schema->table($name)->select( -where => {d_end => {'<' => $today}}, );
Currently DBIx::DataModel has no specific support for schema versioning. See CPAN module DBIx::VersionedSchema, or switch to the DBIx::Class ORM, that has good support for schema versioning.
Use normal SQL syntax for aggregators, and give them column aliases (with a vertical bar |) in order to retrieve the results.
|
my $row = $source->select(-columns => [qw/MAX(col1)|max_col1 AVG(col2)|foo COUNT(DISTINCT(col3))|bar/], -where => ..., -result_as => 'firstrow'); print "max is : $row->{max_col1}, average is $row->{foo}";
Or you can dispense with column aliases, and retrieve the results directly into an arrayref, using -result_as => 'flat_arrayref' :
-result_as => 'flat_arrayref'
my $array_ref = $source->select(-columns => [qw/MAX(col1) AVG(col2) COUNT(DISTINCT(col3))/], -where => ..., -result_as => 'flat_arrayref'); my ($max_col1, $avg_col2, $count_col3) = @$array_ref;
Caveat: currently, from_DB handlers do not apply to aggregator functions. So if the aggregated result needs any transformation, you have to specify a column type for it :
my $row = $source->select( -columns => [qw/MAX(d_begin)|max_d_begin MIN(d_end)|min_d_end .../], -where => ..., -column_types => {Date_simple => [qw/max_d_begin min_d_end/], -result_as => 'firstrow' );
Like above: normal SQL syntax and column aliases.
my $rows = $source->select(-columns => [qw/FUNC(col1,col2)|func (col3+99)|big_col3/], -where => ..., ); print "$_->{func} and $_->{big_col3}" foreach @$rows;
my $subquery = $source1->select(..., -result_as => 'subquery'); my $rows = $source2->select( -columns => ..., -where => {foo => 123, bar => {-not_in => $subquery}} );
There is no need for a hashref inflator: rows returned by a select() can be used directly as hashrefs. For example here is a loop that prints a hash slice from each row :
select()
my $rows = $schema->table($name)->select(...); my @print_cols = qw/col3 col6 col7/; foreach my $row (@$rows) { print @{$row}{@print_cols}; }
In fact, each row is a blessed hashref. This can be a problem with some external modules like JSON that croak when encoding a blessed reference. In that case you can use the unbless function
unbless
foreach my $row (@$rows) { $schema->unbless($row); print to_json($row); }
Create a 'Perl view' to encapsulate your SQL, i.e. a DBIx::DataModel::Source::Table, possibly with a where clause :
where
$meta_schema->define_table( name => 'MyView', db_table => 'TABLE1 EXOTIC JOIN TABLE2 ON ...', where => {col1 => $filter1, col2 => $filter2} parents => [map {meta_schema->table($_)} qw/Table1 Table2/], );
# anonymous sub containing the work to do my $to_do = sub { $table1->insert(...); $table2->delete(...); }; # so far nothing has happened in the database # now do the transaction $schema->do_transaction($to_do);
$schema->do_transaction(sub { do_something(); $schema->do_transaction(sub { some_nested_code(); }); $schema->do_transaction(sub { some_other_nested_code(); }); });
$schema->dbh($initial_dbh); $schema->do_transaction(sub { # start working in $initial_dbh do_something(); # now some work in $other_dbh $schema->do_transaction(sub { some_nested_code(); }, $other_dbh); # here, implicitly we are back in $initial_dbh $schema->do_transaction(sub { some_other_nested_code(); }); }); # commits in both $initial_dbh and $other_dbh are performed here
Override the _singleInsert() method
package MySchema::SomeTable; sub _singleInsert { my ($self) = @_; my $class = ref $self; my ($key_column) = $class->primKey; for (1..$MAX_ATTEMPTS) { my $random_key = int(rand($MAX_RANDOM)); $self->{$key_column} = $random_key; eval {$self->_rawInsert; 1} and return $random_key; # SUCCESS # if duplication error, try again; otherwise die last unless $DBI::errstr =~ $DUPLICATE_ERROR; } croak "cannot generate a random key for $class: $@"; }
First insert an arrayref of subrecords within the main record hashref; then call insert on that main record. See example in insert(). This only works if the two classes are associated through a Composition. A datastructure containing the keys of all generated records can be retrieved by using the option
insert
my $tree_of_keys = $table->insert(..., -returning => {});
# first gather information tree from the database my $author = My::DB::Author->fetch($author_id); my $distribs = $author->expand('distributions'); $_->expand('modules') foreach @$distribs; # then delete the whole tree from the database $author->delete;
This only works if the two classes are associated through a Composition. The expand operations retrieve related records and add them into a tree in memory. Then delete removes from the database all records found in the tree; therefore this is not a "true" cascaded delete, because the client code is responsible for fetching the related records.
expand
delete
True cascaded delete is best implemented directly in the database, rather than at the ORM layer.
Goal : make sure that the record was not touched between the time it was presented to the user (display form) and the time the user wants to update or delete that record.
In order to do this, we will suppose that every record in every table has a timestamp field TS_MODIF, updated automatically by a trigger within the database. Below is a callback function that checks if the timestamp is still valid :
TS_MODIF
sub _check_time_stamp { my ($record, $table, $where) = @_; if ($where) { # this is an update, not an insert my $displayed_timestamp = delete $record->{TS_MODIF}; my $db_record = $record->schema->table($table)->select( -columns => 'TS_MODIF', -where => $where, -for => 'update', # optional, depends on your RDBMS -result_as => 'firstrow', ) or croak "fetch timestamp: could not find record " . join(" / ", %$where); my $db_timestamp = $db_record->{TS_MODIF}; $db_timestamp == $displayed_timestamp or croak "record in $table was modified by somebody else; please " . "refresh your screen and try again"; } }
This callback function can then be registered as an auto_update_column when defining the schema :
DBIx::DataModel->define_schema( class => 'My::Schema', auto_update_columns => {TS_MODIF => \&_check_time_stamp}, );
To install DBIx::DataModel, copy and paste the appropriate command in to your terminal.
cpanm
cpanm DBIx::DataModel
CPAN shell
perl -MCPAN -e shell install DBIx::DataModel
For more information on module installation, please visit the detailed CPAN module installation guide.