See e.g. https://groups.google.com/d/topic/liftweb/1WizPeI8C4o/discussion -- if you load a OneToMany from the database and call delete_!, the MappedOneToMany's children won't be deleted (even if you mixed in Cascade) because objects are lazily initialized. Initialize MappedOneToMany and MappedManyToMany when running reflection to discover MappedFields.