What is the difference between hasOne and hasMany in Laravel?

Question

What is the difference between hasOne and hasMany in Eloquent, and when should you use each?

Answer

hasOne defines a one-to-one relationship. A model owns exactly one related record:

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

$profile = User::find(1)->profile; // single Profile model

hasMany defines a one-to-many relationship. A model owns multiple related records:

// A User has many Posts
class User extends Model
{
    public function posts(): HasMany
    {
        return $this->hasMany(Post::class);
    }
}

$posts = User::find(1)->posts; // Collection of Post models

Key Differences

Eager Loading (avoid N+1)

$users = User::with(['profile', 'posts'])->get();