Below are the answers to our first week's quiz from Course 2 of Tealeaf Academy (regarding associations, relational database, primary vs. foreign keys, mass assignment, etc.).

c2wk1rails_quiz.md

Rails Week 1 Quiz

1. Why do they call it a relational database?
   
   We call it a relational database, because the tables within the database are associated with each other. This association can be created with primary/foreign keys and various syntax.

2. What is SQL?
   
   SQL stands for "Sequence Query Language" and it is used to manage the operations of a relational database.

3. There are two predominant views into a relational database. What are they, and how are they different?
   
   The two predominant views are the data and schema views. Data view displays like a spreadsheet, with the table columns at the top and rows of data per each object instance. A schema view shows us the column names and the value type of each column.

4. In a table, what do we call the column that serves as the main identifier for a row of data? We're looking for the general database term, not the column name.
   
   We call this the "primary key".

5. What is a foreign key, and how is it used?
   
   A foreign key is the identifier that connects an association with the models involved. The foreign key is always on the "many" side and is always in an integer type.

6. At a high level, describe the ActiveRecord pattern. This has nothing to do with Rails, but the actual pattern that ActiveRecord uses to perform its ORM duties.
   
   ActiveRecord is a way to access the database. A database table is related to a class. An object of that class is created as a row in the table. This object can have different attribute values shown as the columns in the table. We can create, retrieve, update, and delete the object instances by altering the database table.

7. If there's an ActiveRecord model called "CrazyMonkey", what should the table name be?
   
   By Rails convention, the table name should be "crazy_monkeys" by using "CrazyMonkey".tableize.

8. If I'm building a 1:M association between Project and Issue, what will the model associations and foreign key be?

   In the Project model:

   class Project < ActiveRecord::Base
       has_many :issues, foreign_key: :project_id
   end
   

   In the Issue model:

   class Issue < ActiveRecord::Base
       belongs_to :project, foreign_key: :project_id
   end
   

   The foreign key will be project_id.

9. Given this code

   class Zoo
       has_many :animals
   end
   

   What do you expect the other model to be and what does database schema look like?
   The Animal model:

   class Animal
       belongs_to :zoo
   end
   

   The database schema will have tables named:

   • zoos table with a primary key of id
   • animals table with a primary key of id and foreign key of zoo_id

   What are the methods that are now available to a zoo to call related to animals?
   zoo.animals will return all a list of all of the animals. zoo.animals.first will return the first row of data in the animals table.

   You can also iterate through the list of a zoo's animals and display certain properties of the animals.

   How do I create an animal called "jumpster" in a zoo called "San Diego Zoo"?
   In the Rails console, enter the following commands:

   $ zoo = Zoo.create(name: 'San Diego Zoo') # => Sets the primary id of 1 for San Diego Zoo
   $ animal = Animal.create(name: 'jumpster', zoo_id: 1)
   

10. What is mass assignment? What's the non-mass assignment way of setting values?
    
    Mass assignment allows us to assign multiple values to attributes with only a single assignment operator.

    Mass assignment:

    $ Post.new(title: 'My first post', topic: 'Life')
    $ Post.create(title: 'My first post', topic: 'Life')
    

    Non-mass assignment:

    post = Post.new
    post.title = 'My first post'
    post.topic = 'Life'
    

11. What does this code do? Animal.first
    
    This will return the first row of data for the first Animal instance object in the animals table.

12. If I have a table called "animals" with columns called "name", and a model called Animal, how do I instantiate an animal object with name set to "Joe". Which methods makes sure it saves to the database?

    $ animal = Animal.create(name: 'Joe') # => Using "create" will hit the database and automatically saves it.
    

    $ animal = Animal.new(name: 'Joe') # => Using "new" will require you to use the save method afterwards to save it to the database.
    $ animal.save
    

13. How does a M:M association work at the database level?
    
    On the database level of a M:M association, we use a join table to support it. Both of the primary models will each have a 1:M association with the join table. By using the has_many :through technique, we are able to create an indirect M:M association with the two primary models.

14. What are the two ways to support a M:M association at the ActiveRecord model level? Pros and cons of each approach?
    
    The two ways to support a M:M association are the has_many :through and has_and_belongs_to_many methods.

    has_many :through requires an explicit join model and a join table, but it is more flexible and we can add additional attributes to the join table. has_and_belongs_to_many doesn't require a join model or a join table, but it is less flexible and we cannot add additional attributes to the join table.

15. Suppose we have a User model and a Group model, and we have a M:M association all set up. How do we associate the two?

    We will need to use a join model(UserGroup) and table(user_groups) in this situation.

    The User model:

    class User < ActiveRecord::Base
        has_many :user_groups, foreign_key: :user_id
        has_many :groups, through: :user_groups
    end
    

    The User_Group model:

    class UserGroup < ActiveRecord::Base
        belongs_to :user, foreign_key: :user_id
        belongs_to :group, foreign_key: :group_id
    end
    

    The Group model:

    class Group < ActiveRecord::Base
        has_many :user_groups, foreign_key: :group_id
        has_many :users, through: :user_groups
    end