Sometimes in your Rails app you may want to find records that have no has_many items or has at least one item. Heres how to do this:
### Find all records with at least one child
Parent.join(:children).uniq.all
# or
Parent.includes(:children).where("children.id IS NOT NULL")
# or Rails 5
Parent.left_outer_joins(:children).where.not(children: {id: nil})
### Find all records with no children
Parent.includes(:children).where(children: {id: nil})
# or Rails 5
Parent.left_outer_joins(:children).where(children: {id: nil})
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