One-to-one (hasOne, belongsTo) in Laravel - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a one-to-one relationship in the User model using hasOne.

Laravel

public function profile() {
    return $this->[1](Profile::class);
}

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

AhasMany

BbelongsTo

ChasOne

DbelongsToMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using belongsTo instead of hasOne here.

Confusing hasOne with hasMany.

The hasOne method defines a one-to-one relationship where the current model owns the related model.

2fill in blank

medium

Complete the code to define the inverse one-to-one relationship in the Profile model using belongsTo.

Laravel

public function user() {
    return $this->[1](User::class);
}

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

AbelongsTo

BhasOne

ChasMany

DbelongsToMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using hasOne instead of belongsTo here.

Mixing up which model holds the foreign key.

The belongsTo method defines the inverse of a one-to-one or one-to-many relationship, pointing back to the owning model.

3fill in blank

hard

Fix the error in this User model relationship method to correctly define a one-to-one relation.

Laravel

public function profile() {
    return $this->[1](Profile::class)->withTimestamps();
}

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

AhasOne

BbelongsTo

ChasMany

DbelongsToMany

Attempts:

3 left

💡 Hint

Common Mistakes

Using belongsTo instead of hasOne.

Trying to use hasMany for one-to-one.

The hasOne method is correct for one-to-one ownership. The withTimestamps() method is not valid here and should be removed, but the blank focuses on the relationship method.

4fill in blank

hard

Fill both blanks to define a one-to-one relationship with a custom foreign key and local key.

Laravel

public function passport() {
    return $this->[1](Passport::class, '[2]', 'id');
}

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

AhasOne

BbelongsTo

Cuser_id

Dpassport_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using belongsTo instead of hasOne here.

Using the wrong foreign key name.

Use hasOne to define the relationship. The foreign key on the Passport model is usually user_id.

5fill in blank

hard

Fill all three blanks to define the inverse one-to-one relationship with custom keys.

Laravel

public function user() {
    return $this->[1](User::class, '[2]', '[3]');
}

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

AbelongsTo

Bpassport_id

Cid

Duser_id

Attempts:

3 left

💡 Hint

Common Mistakes

Using hasOne instead of belongsTo here.

Mixing up foreign key and owner key names.

The belongsTo method defines the inverse relation. The foreign key on this model is user_id, and the owner's key is id.

Practice

1. In Laravel, when defining a one-to-one relationship, which method should you use on the model that owns the other model?

easy

A. hasOne

B. belongsTo

C. hasMany

D. belongsToMany

Solution

1. Step 1: Understand ownership in one-to-one

   The model that owns the other model is the one that does not have the foreign key.

2. Step 2: Identify the correct method for ownership

   In Laravel, the owning model uses hasOne to define the relationship.

3. Final Answer:

   hasOne -> Option A

4. Quick Check:

   Owning model uses hasOne [OK]

Hint: Owning model uses hasOne, foreign key model uses belongsTo [OK]

Common Mistakes:

• Using belongsTo on the owning model
• Confusing hasOne with hasMany
• Using belongsToMany for one-to-one

2. Which of the following is the correct syntax to define a belongsTo relationship in a Laravel model?

easy

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

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

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

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

Solution

1. Step 1: Recall belongsTo syntax

   The belongsTo method is used on the model with the foreign key and is called like return $this->belongsTo(Model::class);.

2. Step 2: Match the correct syntax

   public function user() { return $this->belongsTo(User::class); } matches the correct belongsTo syntax exactly.

3. Final Answer:

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

4. Quick Check:

   belongsTo syntax uses belongsTo(Model::class) [OK]

Hint: belongsTo uses return $this->belongsTo(Model::class) [OK]

Common Mistakes:

• Using hasOne instead of belongsTo
• Forgetting parentheses after belongsTo
• Using belongsToMany for one-to-one

3. Given these two Laravel models:

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

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

What will $user->profile->phone return if the user has a profile with phone number '123-456-7890'?

medium

A. An array of profiles

B. null

C. An error because profile() is not defined

D. '123-456-7890'

Solution

1. Step 1: Understand the relationship

   User has one Profile, so $user->profile returns the related Profile model instance.

2. Step 2: Access the phone attribute

   Accessing $user->profile->phone returns the phone value from the Profile model, which is '123-456-7890'.

3. Final Answer:

   '123-456-7890' -> Option D

4. Quick Check:

   hasOne returns single related model [OK]

Hint: hasOne returns single model, access attributes directly [OK]

Common Mistakes:

• Expecting an array instead of a single model
• Confusing belongsTo and hasOne roles
• Assuming null when profile exists

4. You have these models:

class Author extends Model {
  public function biography() {
    return $this->hasOne(Biography::class);
  }
}

class Biography extends Model {
  public function author() {
    return $this->belongsTo(Author::class);
  }
}

But when you try $author->biography, it returns null even though the biography exists in the database. What is the most likely cause?

medium

A. The Biography model is missing the hasOne method.

B. The Author model should use belongsTo instead of hasOne.

C. The Biography model's foreign key column name doesn't match Laravel's default 'author_id'.

D. The database table for Biography is missing entirely.

Solution

1. Step 1: Check foreign key conventions

   Laravel expects the foreign key in Biography table to be 'author_id' by default for belongsTo.

2. Step 2: Identify mismatch causes null

   If the foreign key column is named differently, Laravel cannot find the related record, so $author->biography returns null.

3. Final Answer:

   The Biography model's foreign key column name doesn't match Laravel's default 'author_id'. -> Option C

4. Quick Check:

   Foreign key name mismatch causes null relation [OK]

Hint: Check foreign key column names match Laravel defaults [OK]

Common Mistakes:

• Switching hasOne and belongsTo methods incorrectly
• Assuming missing method causes null instead of key mismatch
• Ignoring database schema foreign key names

5. You want to create a one-to-one relationship between Car and Engine models where each car has exactly one engine. The engines table has a foreign key car_id. Which is the correct way to define the relationship in both models?

hard

A. In Car model: public function engine() { return $this->belongsTo(Engine::class); }In Engine model: public function car() { return $this->hasOne(Car::class); }

B. In Car model: public function engine() { return $this->hasOne(Engine::class); }In Engine model: public function car() { return $this->belongsTo(Car::class); }

C. In Car model: public function engine() { return $this->hasMany(Engine::class); }In Engine model: public function car() { return $this->belongsTo(Car::class); }

D. In Car model: public function engine() { return $this->belongsToMany(Engine::class); }In Engine model: public function car() { return $this->belongsToMany(Car::class); }

Solution

1. Step 1: Identify foreign key location

   The foreign key car_id is in the engines table, so Engine belongs to Car.

2. Step 2: Define relationships accordingly

   Car has one Engine (hasOne), Engine belongs to Car (belongsTo).

3. Final Answer:

   Car uses hasOne, Engine uses belongsTo -> Option B

4. Quick Check:

   Foreign key in engines means Engine belongsTo Car [OK]

Hint: Foreign key in table means that model belongsTo owner [OK]

Common Mistakes:

• Reversing hasOne and belongsTo roles
• Using hasMany for one-to-one
• Using belongsToMany for one-to-one