Column types and attributes in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Identify the correct syntax for adding a string column with a default value

Which option correctly adds a name column of type string with a default value of 'guest' in a Rails migration?

Ruby on Rails

class AddNameToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :name, :string, default: 'guest'
  end
end

A add_column :users, :name, :string, default => 'guest'

B add_column :users, :name, :string, default: 'guest'

C add_column :users, :name, :string, default_value: 'guest'

D add_column :users, :name, :string, :default => 'guest'

💡 Hint

Look for the correct keyword argument syntax for default values in Ruby.

In Rails migrations, the default value for a column is set using the keyword argument default:. Option B uses the correct syntax. Option B uses an invalid keyword default_value. Option B uses an incorrect hash rocket syntax without a symbol key. Option B uses a hash rocket but the symbol is passed as a symbol argument instead of a keyword argument, which is invalid here.

❓ component_behavior

intermediate

What is the effect of null: false on a column?

In a Rails migration, what does adding null: false to a column definition do?

Ruby on Rails

add_column :users, :email, :string, null: false

A Makes the column optional in Rails validations

B Allows the column to accept NULL values

C Sets the default value of the column to false

D Prevents the column from accepting NULL values in the database

💡 Hint

Think about database constraints and what null: false means.

The null: false option adds a database-level constraint that disallows NULL values in that column. This means the database will reject any record where this column is NULL. It does not set a default value or affect Rails validations directly.

❓ state_output

advanced

What is the default limit for a string column in Rails migrations?

When you create a string column in a Rails migration without specifying a limit, what is the default maximum length in the database?

Ruby on Rails

add_column :users, :username, :string

A 65,535 characters

B No limit

C 255 characters

D 191 characters

💡 Hint

Consider common database defaults for VARCHAR columns.

Rails maps the string type to a VARCHAR(255) column by default in most SQL databases. This means the maximum length is 255 characters unless you specify a different limit.

🔧 Debug

advanced

Why does this migration raise an error?

Given the migration code below, why does it raise an error when run?

Ruby on Rails

class AddAgeToUsers < ActiveRecord::Migration[7.0]
  def change
    add_column :users, :age, :integer, limit: 10
  end
end

A The limit option for integer columns must be 1, 2, 3, 4, or 8 bytes; 10 is invalid

B The column name 'age' is reserved and cannot be used

C The migration is missing a default value for the age column

D The limit option is only valid for string columns, not integers

💡 Hint

Check the valid byte sizes for integer limits in Rails migrations.

In Rails, the limit option for integer columns specifies the number of bytes and must be one of 1, 2, 3, 4, or 8. Using 10 is invalid and causes an error. The limit option is valid for integers, the column name 'age' is allowed, and default values are optional.

🧠 Conceptual

expert

How does Rails handle decimal column precision and scale?

In a Rails migration, when defining a decimal column with precision and scale, what do these two attributes control?

Ruby on Rails

add_column :products, :price, :decimal, precision: 8, scale: 2

A <code>precision</code> is total digits stored; <code>scale</code> is digits after the decimal point

B <code>precision</code> is digits after the decimal; <code>scale</code> is total digits stored

C <code>precision</code> sets the maximum value; <code>scale</code> sets the minimum value

D <code>precision</code> and <code>scale</code> are synonyms and control total digits

💡 Hint

Think about how numbers with decimals are stored in databases.

In Rails migrations, precision defines the total number of digits that can be stored, including both sides of the decimal point. scale defines how many digits can be stored after the decimal point. For example, precision 8 and scale 2 means up to 6 digits before and 2 digits after the decimal.