OOP

Question 1

Write the migration to rename a column in a table?

Answer 1

class RenameOldColumnInTable < ActiveRecord::Migration
def change
rename_column :table, :old_column_name, :new_column
end
end

Question 2

What is a database query?

Answer 2

A DB query is a connection with the DB to read, create, update or delete records.

Question 3

Complete the following model with a presence and uniqueness validation on :github_nickname

Answer 3

Class Developer < ActiveRecord::Base
validates :github_nickname, presence: true, uniqueness: true
end

Question 4

What is the SQL query generated by destroy
------------------
doctor.id
# =>  1
doctor.destroy

Answer 4

This deletes one record in the table doctors.

Question 5

How do you run a pending migrations?

Answer 5

$ rake db:migrate

Question 6

How would you modelize a n:n relation between the following models:

class Post < ActiveRecord::Base
end

class Category < ActiveRecord::Base
end

Answer 6

class CreateCategoriesPosts < ActiveRecord::Migration
create_table :categories_posts do |t|
t.references :post, index: true
t.references :category, index: true
t.timestamps null: false
end
end
———————
And using through in your associations instructions in your models classes:
———————–
class Post < ActiveRecord::Base
has_many :categories_posts
has_many :categories, through: :categories_posts
end

class Category < ActiveRecord::Base
has_many :categories_posts
has_many :posts, through: :categories_posts
end

Question 7

How can we add a a column to a table thanks to a migration?

Answer 7

class AddNewColumntoTable < ActiveRecord::Migration
def change
add_column :table, :new_column, :format
end
end
———————
If you name properly your migration class AddColumnToTable, Rails will autocomplete the code inside the change method

Question 8

Write the migration to add an intern_id foreign key in patients table

Answer 8

class AddInternReferenceToPatiens < ActiveRecord::Migration
def change
add_reference :patiens, :intern, index: true
end
end
——————
Note the second argument :intern and not :intern_id

Question 9

SELECT * FROM doctors WHERE specialty LIKE “%surgery”;

Answer 9

This query returns all doctors having specialty ending with “surgery”(note the %)

Question 10

What symbol is used in a SQL query to get all columns?

Answer 10

SELECT * FROM TABLE

Question 11

What is the SQL keyword to join two tables in a query?

Answer 11

JOIN…ON

SELECT * FROM first_table
JOIN second_table ON second_table.id = first_table.second_table_id;

Question 12

Complete the following model with a regex validation on :email

Answer 12

Class Developer < ActiveRecord::Base
validates :email, format: { with: /\A.@..com\z/ }
end

Question 13

How do you retrieve a specific record of a given ActiveRecord model?

Answer 13

By calling .find(id) on your model
or
By calling .find_by(attribute: value) if you don’t know the id

Question 14

Consider the model Doctor, assuming you already created a DB with doctors tables, how would you add a new doctor in your DB?

Answer 14

dr_house = Doctor.new(name: “greg”)

dr_house.save

Question 15

You start a new project, what is the next step following the user’s stories writing and mockups drawing, and before writing any line of code?

Answer 15

Project steps:
> user's stories
> mockups
> db schema
>> Start coding

Question 16

What is the SQL keyword to retrieve from the DB?

Answer 16

SELECT

Question 17

Give the generic syntax of a migration to add a column to a given table?

Answer 17

class AddColmnToTable < ActiveRecord::Migration
 def change 
     add_column :table, :column, :type
 end
end