postgres sql delete violates foreign key constraint code example

Example: PG::ForeignKeyViolation: ERROR: update or delete on table violates foreign key constraint

has_many :comments, dependent: :delete_all - just automatically delete them when the user is deleted

has_many :comments, dependent: :destroy - like above, but call #destroy on each comment instead of just deleting directly in the db

has_many :comments, dependent: :nullify - don't delete comments when the user is deleted, just null out their user_id column