1.Why do they call it a relational database?
a relationship can be established between the table and another table by creating foreign key, and can assemble related information very quickly.
2.What is SQL?
SQL stands for Structured Query Language.
It's a standard language for accessing to databases.
3.There are two predominant views into a relational database. What are they, and how are they different?
- The data view shows the columns and rows in the tables.
- The scheme view shows the structure of the table, like name, type, key, etc...
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.
Primary key
5.What is a foreign key, and how is it used?
It's a primary key of another tables. It is used for establish a relation between table to table.
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.
An ActiveRecord object shows a row of the tables.
7.If there's an ActiveRecord model called "CrazyMonkey", what should the table name be?
crazy_monkeys
8.If I'm building a 1:M association between Project and Issue, what will the model associations and foreign key be?
Project has many issues, and Issues belongs to project.
project_id would be foreign key.
9.Given this code
class Zoo < ActiveRecord::Base
has_many :animals
end
What do you expect the other model to be and what does database schema look like?
class Animal < ActiveRecord::Base
belongs_to :zoo
end
create_table animals do |t|
t.string "name"
t.integer "zoo_id"
t.timestanps
end
What are the methods that are now available to a zoo to call related to animals?
zoo = Zoo.first
then,
zoo.animals
How do I create an animal called "jumpster" in a zoo called "San Diego Zoo"?
san_diego_zoo = Zoo.create(name: "San Diego Zoo")
jumpster = Animal.create(name: "jumpster")
san_diego_zoo.animals << jumpster
10.What is mass assignment? What's the non-mass assignment way of setting values?
-The mass assignment way
User.create(params[:user])
-The non-mass sssignment way
User.create(name: params[:user][:name])
11.What does this code do? Animal.first
It will fetch the first row of 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?
joe = Animals.new(name: "Joe")
Animal.create method will save to database at the same time.
13.How does a M:M association work at the database level?
It works by joining tables.
14.What are the two ways to support a M:M association at the ActiveRecord model level? Pros and cons of each approach?
- has_many with through option
- has_and_belongs_to_many
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?
class User < ActiveRecord::Base
has_many :groups, through: assignments
has_many :assignments
end
class Group < ActiveRecord::Base
has_many :users, through: assignments
has_many :assignments
end
class Assignment < ActiveRecord::Base
belongs_to :user
belongs_to :group
end