Model generation in Ruby on Rails - Practice Problems & Coding Challenges

Challenge - 5 Problems

📝 Syntax

intermediate

Correct Rails model generation command

Which command correctly generates a Rails model named Article with a string attribute title and a text attribute content?

A rails generate model Article title:text content:string

B rails generate model Article title:string content:text

C rails generate scaffold Article title:string content:text

D rails generate model article title:string content:text

💡 Hint

Model names should be singular and capitalized. Attribute types must match the desired data type.

Option B uses the correct command to generate a model named Article with the specified attributes and types. Option B swaps the types incorrectly. Option B generates a scaffold, not just a model. Option B uses a lowercase model name, which does not follow conventions.

❓ component_behavior

intermediate

Behavior of generated model with validations

Given a Rails model Product generated with name:string and a validation validates :name, presence: true, what happens when you try to save a Product without a name?

Ruby on Rails

class Product < ApplicationRecord
  validates :name, presence: true
end

p = Product.new
p.save

A The save ignores validations and saves the product.

B The save returns true and saves the product with a blank name.

C The save raises a runtime error due to missing name.

D The save returns false and the product is not saved to the database.

💡 Hint

Think about what validations do before saving a record.

The validation prevents saving a product without a name. The save method returns false and the record is not saved. No error is raised.

🔧 Debug

advanced

Fixing migration timestamp mismatch error

You generated a model with rails generate model User email:string but when running rails db:migrate, you get an error about a missing migration file. What is the most likely cause?

A The migration file was deleted or renamed after generation, causing Rails to not find it.

B The model file <code>user.rb</code> is missing in app/models.

C The database.yml file is missing the development database configuration.

D The schema.rb file is corrupted and needs to be deleted.

💡 Hint

Check the migration files folder for the generated migration.

Rails relies on migration files with timestamps to run migrations. If the migration file is missing or renamed, Rails cannot find it and raises an error. The model file missing does not affect migration. Database config or schema.rb issues cause different errors.

❓ state_output

advanced

Result of running a model generator with a reserved word attribute

What happens if you run rails generate model Post class:string and then try to migrate?

A Migration fails with a syntax error because 'class' is a reserved Ruby word.

B Rails renames the 'class' attribute automatically to 'class_field'.

C Migration runs successfully and creates a posts table with a class column.

D Migration runs but the 'class' column is ignored.

💡 Hint

Consider Ruby reserved keywords and their use as column names.

Option C is correct. The generated migration uses `t.string :class`, which is valid Ruby syntax (:class is a symbol) and runs successfully, creating the table with a class column. Although 'class' is reserved, it does not cause a syntax error. Rails does not rename or ignore it.

🧠 Conceptual

expert

Understanding Rails model generation with polymorphic associations

You want to generate a model Comment that belongs to a polymorphic association called commentable. Which command correctly generates the model with the necessary fields?

A rails generate model Comment body:text commentable:references{polymorphic}

B rails generate model Comment body:text commentable_id:integer commentable_type:string

C rails generate model Comment body:text commentable:belongs_to

D rails generate model Comment body:text commentable:polymorphic

💡 Hint

Rails has a special syntax for polymorphic references in generators.

Option A uses the correct syntax with references{polymorphic} to generate both commentable_id and commentable_type columns. Option A manually specifies columns but is not the generator syntax. Options C and A use invalid syntax.