One-to-one (hasOne, belongsTo) in Laravel - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of accessing a related model using hasOne?

Consider a Laravel User model with a hasOne relation to Profile. If you run $user->profile->bio and the user has a profile with bio 'Loves coding', what will be the output?

Laravel

<?php
class User extends Model {
  public function profile() {
    return $this->hasOne(Profile::class);
  }
}

$user = User::find(1);
echo $user->profile->bio;

A Loves coding

B null

C Error: Undefined property

D Empty string

💡 Hint

Remember that hasOne returns the related model instance if it exists.

The hasOne relation returns the related Profile model. Accessing ->bio on it returns the stored bio string.

❓ state_output

intermediate

What happens if belongsTo relation is accessed but related model is missing?

Given a Profile model with a belongsTo relation to User, what is the result of $profile->user->name if the user record was deleted?

Laravel

<?php
class Profile extends Model {
  public function user() {
    return $this->belongsTo(User::class);
  }
}

$profile = Profile::find(1);
echo $profile->user->name;

A null

B Error: Trying to get property 'name' of non-object

C Empty string

D User name string

💡 Hint

Think about what happens if the related user does not exist.

If the related user is missing, $profile->user returns null. Accessing ->name on null causes an error.

📝 Syntax

advanced

Which code correctly defines a one-to-one inverse relation using belongsTo?

Choose the correct belongsTo relation definition inside the Profile model pointing to User.

A public function user() { return $this->hasOne(User::class); }

B public function user() { return $this->hasMany(User::class); }

C public function user() { return $this->belongsTo('User'); }

D public function user() { return $this->belongsTo(User::class); }

💡 Hint

belongsTo is used on the child model to point to the parent.

belongsTo defines the inverse of hasOne. It requires the related class name as a class reference.

🔧 Debug

advanced

Why does eager loading a hasOne relation return an empty collection?

You run $users = User::with('profile')->get(); but $users[0]->profile is null even though the profile exists. What is the most likely cause?

A The profile table is empty

B The hasOne relation is defined with belongsTo instead

C The foreign key in Profile does not match the User primary key

D Eager loading does not work with hasOne relations

💡 Hint

Check the foreign key column names in the database and relation definition.

If the foreign key column in Profile does not match the User primary key, Laravel cannot link the models, so profile is null.

🧠 Conceptual

expert

How does Laravel determine the foreign key name in a hasOne relation by default?

When defining public function profile() { return $this->hasOne(Profile::class); } in User, what foreign key column does Laravel expect in the profiles table by default?

A user_id

B profile_id

C id

D userId

💡 Hint

Laravel uses the parent model name in snake_case plus _id.

By default, Laravel expects the foreign key to be the snake_case of the parent model name plus _id, so 'user_id' in profiles table.