Nested attributes in Ruby on Rails - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to allow nested attributes for comments in the Post model.

Ruby on Rails

class Post < ApplicationRecord
  has_many :comments
  accepts_nested_attributes_for :[1]
end

Drag options to blanks, or click blank then click option'

Aposts

Bcomments

Cusers

Dauthors

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong association name in accepts_nested_attributes_for.

Forgetting to add accepts_nested_attributes_for altogether.

The method accepts_nested_attributes_for is used to allow nested attributes for associated models. Here, it should be used with :comments to enable nested attributes for comments in the Post model.

2fill in blank

medium

Complete the form helper to build fields for nested comments inside the post form.

Ruby on Rails

<%= form_with model: @post do |f| %>
  <%= f.text_field :title %>
  <%= f.fields_for :[1] do |c| %>
    <%= c.text_area :content %>
  <% end %>
<% end %>

Drag options to blanks, or click blank then click option'

Acomments

Bauthors

Cposts

Dusers

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong symbol in fields_for causing no nested fields to appear.

Not matching the association name exactly.

fields_for is used to create form fields for nested attributes. It should match the association name, which is :comments in this case.

3fill in blank

hard

Fix the error in the controller to permit nested comment attributes.

Ruby on Rails

def post_params
  params.require(:post).permit(:title, comments_attributes: [:id, :content, :[1]])
end

Drag options to blanks, or click blank then click option'

Aauthor_id

Buser_id

C_destroy

Dpost_id

Attempts:

3 left

💡 Hint

Common Mistakes

Not permitting :_destroy causes nested record deletion to fail.

Permitting unrelated keys that do not affect nested attributes.

The :_destroy key is used to allow deletion of nested records through nested attributes. It must be permitted in strong parameters to work.

4fill in blank

hard

Fill both blanks to build a nested attributes hash for a new comment with content and mark it for destruction.

Ruby on Rails

post_attributes = {
  title: 'New Post',
  comments_attributes: {
    '0' => { content: [1], [2]: true }
  }
}

Drag options to blanks, or click blank then click option'

A'Great post!'

Bcontent

C_destroy

Ddestroy

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong key name instead of :_destroy.

Putting a non-string value for content.

The content key should have a string value for the comment text. The special key :_destroy with value true marks the nested comment for deletion.

5fill in blank

hard

Fill all three blanks to create a nested attributes hash for updating a comment's content and allowing its destruction.

Ruby on Rails

post_params = {
  post: {
    title: 'Updated Post',
    comments_attributes: {
      '0' => { id: [1], content: [2], [3]: true }
    }
  }
}

Drag options to blanks, or click blank then click option'

A42

B'Updated comment content'

C_destroy

Dcontent

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string instead of a number for id.

Forgetting to include :_destroy to allow deletion.

The id should be the comment's id (number). The content is a string with the new comment text. The :_destroy key with true allows marking the comment for deletion.

Practice

1. What does accepts_nested_attributes_for do in a Rails model?

easy

A. Validates the presence of nested attributes in the parent model.

B. Creates a new database table for nested models automatically.

C. Allows a parent model to accept and save attributes for its associated child models.

D. Generates controller actions for nested resources.

Solution

1. Step 1: Understand the purpose of accepts_nested_attributes_for

   This method is used in a parent model to allow it to accept attributes for its associated child models.

2. Step 2: Recognize what it enables in Rails

   It enables saving or updating child model data through the parent model's form or controller.

3. Final Answer:

   Allows a parent model to accept and save attributes for its associated child models. -> Option C

4. Quick Check:

   accepts_nested_attributes_for = Accept nested child attributes [OK]

Hint: Think: parent model saving child data together [OK]

Common Mistakes:

• Confusing it with database table creation
• Assuming it validates nested attributes automatically
• Thinking it generates controller code

2. Which of the following is the correct syntax to enable nested attributes for a child model named tasks inside a parent model?

easy

A. accepts_nested_attributes_for :tasks

B. accepts_nested_attributes_for :task

C. accepts_nested_attributes_for tasks

D. accepts_nested_attributes_for 'tasks'

Solution

1. Step 1: Identify the correct argument type

   The method expects a symbol representing the association name, which is plural if the association is has_many.

2. Step 2: Match the association name

   Since the child model is tasks (plural), the correct syntax is accepts_nested_attributes_for :tasks.

3. Final Answer:

   accepts_nested_attributes_for :tasks -> Option A

4. Quick Check:

   Use symbol with plural association name [OK]

Hint: Use symbol and plural for has_many associations [OK]

Common Mistakes:

• Using singular instead of plural for has_many
• Passing string instead of symbol
• Omitting colon before association name

3. Given the following models and controller snippet, what will happen when creating a Project with nested tasks_attributes?

class Project < ApplicationRecord
  has_many :tasks
  accepts_nested_attributes_for :tasks
end

class Task < ApplicationRecord
  belongs_to :project
end

# In ProjectsController
params = { project: { name: 'Build App', tasks_attributes: [{ title: 'Design UI' }, { title: 'Write Tests' }] } }
@project = Project.new(params[:project])
@project.save

medium

A. A new project and two associated tasks will be saved in the database.

B. Only the project will be saved; tasks will be ignored.

C. An error will occur because nested attributes are not permitted in the controller.

D. The project will save but tasks will be saved without association.

Solution

1. Step 1: Check model setup for nested attributes

   The Project model uses accepts_nested_attributes_for :tasks, allowing nested task attributes.

2. Step 2: Analyze controller params and save

   The params include tasks_attributes with two tasks. Calling Project.new with these params and then save will save the project and its tasks together.

3. Final Answer:

   A new project and two associated tasks will be saved in the database. -> Option A

4. Quick Check:

   Nested attributes save parent and children together [OK]

Hint: Nested attributes save parent and children in one go [OK]

Common Mistakes:

• Assuming tasks are ignored without explicit permit
• Thinking save fails without controller strong params shown
• Believing tasks save without association

4. Identify the error in the following controller code when trying to save nested attributes:

def project_params
  params.require(:project).permit(:name, tasks_attributes: [:title])
end

@project = Project.new(project_params)
@project.save

Assuming the models are set up correctly with accepts_nested_attributes_for :tasks.

medium

A. The require method should be permit instead.

B. The accepts_nested_attributes_for should be in the controller, not the model.

C. The tasks_attributes key should be a string, not a symbol.

D. The permit method is missing the :id key inside tasks_attributes.

Solution

1. Step 1: Understand strong parameters for nested attributes

   When updating nested records, Rails expects the :id key to identify existing child records.

2. Step 2: Check the permit call

   The permit call only allows :title inside tasks_attributes, missing :id. This causes update failures or errors.

3. Final Answer:

   The permit method is missing the :id key inside tasks_attributes. -> Option D

4. Quick Check:

   Permit :id for nested updates [OK]

Hint: Permit :id inside nested attributes for updates [OK]

Common Mistakes:

• Omitting :id in nested strong params
• Confusing require and permit methods
• Placing accepts_nested_attributes_for in controller

5. You have a Survey model with many questions. You want to allow users to add, update, and remove questions through the survey form. Which combination of code is needed to correctly handle nested attributes and allow question removal?

hard

A. In Survey model: accepts_nested_attributes_for :questions, reject_if: :all_blank
In controller: permit questions_attributes with :content, :_destroy

B. In Survey model: accepts_nested_attributes_for :questions, allow_destroy: true
In controller: permit questions_attributes with :id, :content, :_destroy

C. In Survey model: has_many :questions
In controller: permit questions_attributes with :id, :content

D. In Survey model: accepts_nested_attributes_for :questions
In controller: permit questions_attributes with :content only

Solution

1. Step 1: Enable nested attributes with destroy option

   To allow removal of nested records, accepts_nested_attributes_for must include allow_destroy: true.

2. Step 2: Permit necessary keys in controller

   The controller must permit :id to identify records, :content for data, and :_destroy to mark records for deletion.

3. Final Answer:

   In Survey model: accepts_nested_attributes_for :questions, allow_destroy: true In controller: permit questions_attributes with :id, :content, :_destroy -> Option B

4. Quick Check:

   allow_destroy and permit :_destroy for removals [OK]

Hint: Use allow_destroy and permit :_destroy to remove nested records [OK]

Common Mistakes:

• Forgetting allow_destroy in model
• Not permitting :_destroy in strong params
• Permitting only :content without :id