+Columns and relationships which are excluded from the updates hashref aren't
+touched at all.
+
+=head2 Treatment of belongs_to relations
+
+In case the relationship is included but undefined in the updates hashref,
+all columns forming the relationship will be set to null.
+If not all of them are nullable, DBIx::Class will throw an error.
+
+Updating the relationship:
+
+ my $dvd = $dvd_rs->recursive_update( {
+ id => 1,
+ owner => $user->id,
+ });
+
+Clearing the relationship (only works if cols are nullable!):
+
+ my $dvd = $dvd_rs->recursive_update( {
+ id => 1,
+ owner => undef,
+ });
+
+=head2 Treatment of might_have relationships
+
+In case the relationship is included but undefined in the updates hashref,
+all columns forming the relationship will be set to null.
+
+Updating the relationship:
+
+ my $user = $user_rs->recursive_update( {
+ id => 1,
+ address => {
+ street => "101 Main Street",
+ city => "Podunk",
+ state => "New York",
+ }
+ });
+
+Clearing the relationship:
+
+ my $user = $user_rs->recursive_update( {
+ id => 1,
+ address => undef,
+ });
+
+=head2 Treatment of has_many relations
+
+If a relationship key is included in the data structure with a value of undef
+or an empty array, all existing related rows will be deleted, or their foreign
+key columns will be set to null.