ActiveRecord

Question 0

Starting with a Student model, how would you join to the schools table and then narrow the results to include only public schools (“category” is “public”)?

Answer 0

Student.join(:schools).where(schools: {category: “public”})

OR

Student.join(:schools).where(“schools.category” => “public”)

Question 1

How would you retrieve from the data store a group of students who are between the ages of 7 and 9?

Answer 1

Student.where(age: 7..9)
# OR
Student.where(age: [7,8,9])

Question 2

How do you override accessors for models?

Answer 2

With the read_attribute and write_attribute methods.

Question 3

Due to the nature of the web, the data input by the user will always be strings. ActiveRecord, however, tries to coerce the data into the specified column’s type. How do you access the original data?

Answer 3

model._before_type_cast

Question 4

How can you store complex data in a single text column?

Answer 4

Model < ActiveRecord::Base
serialize :complex_data
end

Question 5

How can you force serialized data to be of a specific class?

Answer 5

Pass the class name as the second argument to the serialize method:

serialize :attribute, OpenStruct

Question 6

How do you validate that a string matches the pattern /\w+/?

Answer 6

validates :attributes, format: { with: /\w+/ }

Question 7

How do you validate that a string is not either “a,” “the,” or “or”?

Answer 7

validates :attribute, exclusion: { in: %w(a the or) }

Question 8

How do you validate that a shirt size is either “small,” “medium,” or “large?”

Answer 8

validates :size, inclusion: { in: %w(small medium large) }

Question 9

How do you validate that a password at least 6 characters long?

Answer 9

validates :password, length: { minimun: 6 }

Question 10

How do you validate that a password is less than 20 characters long?

Answer 10

validates :password, length: { maximum: 20 }

Question 11

How do you validate that a password is in between 6 and 20 characters?

Answer 11

validates :password, length: { in: 6..20 }

Question 12

How do you validate that a string is exactly 25 characters long?

Answer 12

validates :attribute, length: { is: 25 }

Question 13

For length validations, which symbols can you use for error messages?

Answer 13

:wrong_length
:too_long
:too_short

Question 14

How do you validate that a string has at least 300 words?

Answer 14

validates :attribute, length: {
minimum: 300,
tokenizer: lambda { |str| str.scan(/\w+/) }
}

Question 15

How do you validate that :age is a number?

Answer 15

validates :age, numericality: true

Question 16

How do you confirm that :age in an integer

Answer 16

validates :age, numericality: { only_integer: true }

Question 17

What are the acceptable constraints for numericality?

Answer 17

\:greater_than
\:less_than
\:greater_than_or_equal_to
\:less_than_or_equal_to
\:equal_to
\:even
\:odd

Question 18

How do you confirm that a string is not nil or blank?

Answer 18

validates :attribute, presence: true