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

<iframe width="560" height="315" src="https://www.youtube.com/embed/MXkmCTywFFM?rel=0&showinfo=0" frameborder="0" allowfullscreen></iframe>

Note: cd into the lecture_kit directory before running any commands like bundle, bin/rake`, etc.

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 bin/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