Active Record Relationships - More Models

SWBATs

Practice deciding where the id should live in associated tables (remember that it is the joiner's responsibility to know about the other id's)
Practice adding new models and setting up associations from scratch

WATCH THIS FIRST

ERD

Currently, our ERD looks as following:

Category :name
    |
    ^
  Plant ----< PlantParenthood >---- PlantParent
   :species      :plant_id            :name
   :color        :plant_parent_id     :responsible
   :bought       :affection           :age
   :fussy
   :category_id

Currently, one plant can have only one category. This does not represent the real-world situation (some plants are indoor, some are outdoor and some are both). We also see that the only relationship between a plant and a person is "parenthood" (ownership) but what about the moment when someone else waters your plants for you when you're away? They are not owners but they do interact with the plant.

At the end of the practice, our ERD will look as following:

  Category
    |
    ^
  PlantCategory
    V
    |
  Plant ----< PlantParenthood >----   Person
    |                                   |
    |                                   |
    |                                   |
     --------< Watering >---------------

Description of the models

Category: it is a category of the plant, for example: "leafy", "succulent", "indoor", "outdoor"
Plant: self-explanatory
PlantCategory: since now Plant can have many Categories and vice-versa, we have a many-to-many relationship and need a joiner;
Person: since not everyone interacting with the plant will be a plant_parent, let's change the name of this model to the Person
PlantParenthood: describes a relationship of ownership between a person and a plant
Watering: describes every situation when a person waters the plant

Roadmap

Make Plant-Category relationship a many-to-many

video
finished code
create a new migration: delete the category_id from Plant + migrate
create a new migration: introduce a new table + migrate
create a corresponding model
add associations
test in seeds

Change the name of the `PlantParent` to `Person`

video
finished code
create a new migration: change the name of the table + migrate
change the name of the model file and model name
in all the model files, replace plant_parent and plant_parents with person and people
in seeds, change the model name everywhere
run rake db:seed and check how many people you have and whether you can check number of people associated with a plant (e.g. Plant.first.people.count) or a person (e.g. Person.first.plants) — this should error out! Debug it or watch the video.

Introduce a `Watering` model

Since it's a joiner, it will hold the ids of the other models.

video
finished code
create a new migration: introduce a new table + migrate — remember to add t.timestamps to the table, we will need that to see all the Waterings that happened!
create a corresponding model
add associations — please refer to the video, this one is tricky!
test in seeds

Add behavior

finished code
Person#water_plant: accepts an argument of a plant and creates a new instance of Watering between the person and the plant; if there is an associated PlantParenthood with both, this method also increases the value of affection by one
- video
PlantParenthood#cap_affection: introduces a cap on the affection value at 11_000
- video
Plant#number_of_days_since_the_last_watering: puts "I was watered NUMBER days ago"
- video

dexterfitch/phase-3-ar-more-models-practice