Set prediction data for existing planting and crops
user
```ruby
class SetPredictionData < ActiveRecord::Migration
  def change
    say "Updating all plantings time to first harvest"
    Planting.all.each(&:update_harvest_days)
    say "Updating crop median time to first harvest, and lifespan"
    Crop.all.each do |crop|
      crop.update_lifespan_medians
      crop.update_harvest_medians
    end
  end
end
```
assistant