doctrine2/manual/docs/Mapping object relations - Composites and aggregates.php

Doctrine supports aggregates and composites. When binding composites you can use methods Doctrine_Record::ownsOne() and Doctrine_Record::ownsMany(). When binding
aggregates you can use methods Doctrine_Record::hasOne() and Doctrine_Record::hasMany(). Basically using the owns* methods is like adding a database level ON CASCADE DELETE
constraint on related component with an exception that doctrine handles the deletion in application level.
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In Doctrine if you bind an Email to a User using ownsOne or ownsMany methods, everytime User record calls delete the associated
Email record is also deleted.
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Then again if you bind an Email to a User using hasOne or hasMany methods, everytime User record calls delete the associated
Email record is NOT deleted.