Lazy loading and N+1 prevention in Laravel - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to eager load the 'posts' relationship for all users.

Laravel

$users = User::[1]('posts')->get();

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

Awith

Bload

Cselect

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'load' instead of 'with' on the query builder causes errors.

Using 'select' only chooses columns, not relationships.

Using with('posts') tells Laravel to eager load the posts relationship, preventing N+1 queries.

2fill in blank

medium

Complete the code to lazy load the 'comments' relationship on an existing $post model.

Laravel

$post->[1]('comments');

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

Aload

Bwith

CeagerLoad

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'with' on a model instance instead of a query builder.

Using non-existent methods like 'eagerLoad' or 'fetch'.

The load method is used on an existing model instance to lazy load relationships.

3fill in blank

hard

Fix the error in the code to prevent N+1 queries when accessing each user's posts count.

Laravel

foreach ($users as $user) {
    echo $user->posts->count();
}

// Fix by eager loading posts count:
$users = User::[1]('posts')->get();

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

AloadCount

BwithCount

CcountWith

DwithPostsCount

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'loadCount' which is a method on model instances, not query builder.

Using made-up methods like 'countWith' or 'withPostsCount'.

The withCount method eager loads the count of related models, preventing N+1 queries when counting posts.

4fill in blank

hard

Fill both blanks to eager load 'comments' and 'author' relationships for posts.

Laravel

$posts = Post::[1](['comments', [2]])->get();

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

Awith

Bload

C'author'

D'user'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'load' instead of 'with' on the query builder.

Using 'user' instead of 'author' if the relationship is named 'author'.

Use with to eager load multiple relationships. The 'author' relationship is commonly named for the user who wrote the post.

5fill in blank

hard

Fill all three blanks to eager load 'tags', count 'comments', and filter posts with more than 5 comments.

Laravel

$posts = Post::[1]('tags')->[2]('comments')->having('[3]', '>', 5)->get();

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

Awith

BwithCount

Ccomments_count

Dload

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'load' instead of 'with' on the query builder.

Using 'comments' instead of 'comments_count' in having clause.

Use with('tags') to eager load tags, withCount('comments') to get comments count, and filter with having('comments_count', '>', 5).

Practice

1. What is the main purpose of using with() in Laravel Eloquent queries?

easy

A. To delete related models automatically

B. To load related models eagerly and prevent the N+1 query problem

C. To delay loading related models until they are accessed

D. To paginate the main query results

Solution

1. Step 1: Understand lazy vs eager loading

   Lazy loading delays loading related data until accessed, causing multiple queries (N+1 problem).

2. Step 2: Role of with()

   The with() method loads related models eagerly in one query, preventing multiple queries.

3. Final Answer:

   To load related models eagerly and prevent the N+1 query problem -> Option B

4. Quick Check:

   Eager loading = with() usage [OK]

Hint: Use with() to load relations early and avoid many queries [OK]

Common Mistakes:

• Confusing lazy loading with eager loading
• Thinking with() delays loading
• Assuming with() deletes data
• Mixing with() with pagination

2. Which of the following is the correct syntax to eager load the 'comments' relation on a Post model?

easy

A. $posts = Post::with('comments')->get();

B. $posts = Post::load('comments')->get();

C. $posts = Post::eager('comments')->get();

D. $posts = Post::fetch('comments')->get();

Solution

1. Step 1: Identify Laravel eager loading method

   Laravel uses with() to eager load relations, not load() or others in this context.

2. Step 2: Check method chaining and syntax

   with('comments') is called before get() to eager load comments with posts.

3. Final Answer:

   $posts = Post::with('comments')->get(); -> Option A

4. Quick Check:

   Eager load syntax = with() before get() [OK]

Hint: Remember: with() before get() for eager loading [OK]

Common Mistakes:

• Using load() statically instead of on model instance
• Using non-existent methods like eager() or fetch()
• Calling with() after get()

3. Given the code below, what will be the total number of database queries executed?

 $users = User::all();
foreach ($users as $user) {
  echo $user->posts->count();
}

medium

A. N+1 queries, where N is the number of users

B. 1 query

C. N queries, where N is the number of posts

D. 2 queries regardless of users count

Solution

1. Step 1: Analyze the initial query

   User::all() runs 1 query to get all users.

2. Step 2: Check relation access inside loop

   Accessing $user->posts triggers a query per user (lazy loading), causing N additional queries.

3. Final Answer:

   N+1 queries, where N is the number of users -> Option A

4. Quick Check:

   Lazy loading inside loop = N+1 queries [OK]

Hint: Accessing relations in loop without with() causes N+1 queries [OK]

Common Mistakes:

• Assuming only 1 query runs
• Confusing number of queries with posts count
• Thinking 2 queries run regardless of data size

4. Identify the error in the following code that tries to prevent N+1 queries:

 $orders = Order::with('items');
foreach ($orders as $order) {
  echo $order->items->count();
}

medium

A. Incorrect relation name 'items', should be 'item'

B. Loop variable should be $orders not $order

C. Using with() causes lazy loading, should use load()

D. Missing get() after with() to execute the query

Solution

1. Step 1: Check query execution

   Order::with('items') builds a query but does not execute it without get() or similar.

2. Step 2: Effect on foreach loop

   Without get(), $orders is a query builder, not a collection, so foreach will error.

3. Final Answer:

   Missing get() after with() to execute the query -> Option D

4. Quick Check:

   Always call get() to run query after with() [OK]

Hint: Add get() after with() to fetch data [OK]

Common Mistakes:

• Forgetting to execute query with get()
• Assuming with() runs query immediately
• Confusing relation names without checking model
• Misunderstanding foreach variable naming

5. You want to display a list of authors with their books and each book's reviews without causing N+1 queries. Which is the best way to write the query?

hard

A. $authors = Author::with('reviews')->get();

B. $authors = Author::with('books')->get(); foreach ($authors as $author) { $author->books->load('reviews'); }

C. $authors = Author::with('books.reviews')->get();

D. $authors = Author::all(); foreach ($authors as $author) { foreach ($author->books as $book) { echo $book->reviews->count(); } }

Solution

1. Step 1: Understand nested eager loading

   To avoid N+1, load related models and their relations in one query using dot notation.

2. Step 2: Analyze options for efficiency

   $authors = Author::with('books.reviews')->get(); uses with('books.reviews') to eager load books and their reviews together, preventing multiple queries.

3. Final Answer:

   $authors = Author::with('books.reviews')->get(); -> Option C

4. Quick Check:

   Nested eager loading = dot notation in with() [OK]

Hint: Use dot notation in with() for nested relations [OK]

Common Mistakes:

• Loading relations inside loops causing N+1
• Not eager loading nested relations together
• Using wrong relation names
• Assuming with('reviews') loads nested reviews