=head1 NAME
DBIx::Class::Manual::SQLHackers::DELETE - DBIx::Class for SQL Hackers - DELETE
=over
=item L<Introduction|DBIx::Class::Manual::SQLHackers::Introduction>
=item L<CREATE|DBIx::Class::Manual::SQLHackers::CREATE>
=item L<INSERT|DBIx::Class::Manual::SQLHackers::INSERT>
=item L<SELECT|DBIx::Class::Manual::SQLHackers::SELECT>
=item L<UPDATE|DBIx::Class::Manual::SQLHackers::UPDATE>
=item DELETE
=item L<BEGIN, COMMIT|DBIx::Class::Manual::SQLHackers::Transactions>
=back
=head1 DELETEing data
=head2 Delete a single row based on the primary key
DELETE FROM users
WHERE id = 1;
The simplest form of delete removes a single row from a table using
the primary key value. We B<find> the row, then call the B<delete>
method on it. B<delete> can be called on any result row object.
=over
=item 1. Create a Schema object representing the database you are working with:
my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db');
=item 2. Call the B<find> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to delete:
my $fred_user = $schema->resultset('User')->find({ id => 1 });
=item 3. Call B<delete> on the row object:
$fred_user->delete;
=back
This can also be done as one statement, skipping the extra temporary
variable, if it is not needed later:
$schema->resultset('User')->find({ id => 1 })->delete;
In the first variant, the $fred_user row object will still contain the
last known contents of Fred's data. A call to $fred_user->L<in_storage|DBIx::Class::Row/in_storage> will return
false (0), showing that the row object is no longer connected to a actual
database row.
=head2 Delete one or more rows based on a WHERE clause
DELETE FROM posts
WHERE created_date <= '2000-01-01';
Use a ResultSet to define the WHERE clause using B<search>, then call
the B<delete> method on it directly.
=over
=item 1. Create a Schema object representing the database you are working with:
my $schema = MyDatabase::Schema->connect('dbi:SQLite:my.db');
=item 2. Call the B<search> method on the resultset for the L<ResultSource|DBIx::Class::ResultSource> you wish to delete:
my $old_posts = $schema->resultset('Post')->search({
created_date => { '<=' => '2000-01-01' },
});
=item 3. Call B<delete> on the row object:
$old_posts->delete;
=back
Unlike the single row deletion above, the contents of the rows to be
deleted are never fetched from the database, so no record of them now
remains.
NOTE: Calling B<delete> on a ResultSet object will not run any
overridden B<delete> methods in your Result Classes or any loaded
Components. To force these to run, call B<delete_all> instead:
$old_posts->delete_all();
This will also issue a separate delete statement for each row to be removed.
=head2 Cascading deletes
DELETE FROM users
WHERE id = 1;
DELETE FROM comments
WHERE user_id = 1;
Cascading deletes ensure the integrity of your data, if a User row is
removed, then any items belonging to that user (for example comments
created by the user), should also be removed.
NOTE: This is a rather drastic action, to prevent problems in your
application, consider de-activating accounts instead of removing them!
For the time being DBIx::Class defaults to cascade deletion for the
following types of relationships: B<has_many>, B<has_one>,
B<might_have>. That is, it will automatically issue the above
statements. It is recommended not to rely on this implicit behavior,
as it will be deprecated in a later version of DBIC. Instead declare
proper cascading constraints in your RDBMS as described in
L<DBIx::Class::Manual::SQLHackers::CREATE/Table creation with
references>.
If your database is already properly set up to cascade deletes for you,
you can noop DBIx::Class' extra cascading statements:
__PACKAGE__->has_many('posts',
'MyDatabase::Schema::Result::Post',
'user_id',
{ cascade_delete => 0 });