What is a One-to-One Relationship?

A one-to-one relationship means that a row in one table is linked to exactly one row in another table.

👉 Example:

• Each employee has exactly one profile.
• Each profile belongs to exactly one employee.

Employee: 1 ↔ 1 Profile

Migration:

Use this command to generate a migration for creating a tables:

php artisan make:migration create_one_to_one_tables

Migration File

public function up(): void
{
    Schema::create('employees', function (Blueprint $table) {
        $table->id();
        $table->string('name');
        $table->timestamps();
    });

    Schema::create('profiles', function (Blueprint $table) {
        $table->id();
        $table->foreignId('employee_id')->constrained()->onDelete('cascade');
        $table->string('bio')->nullable();
        $table->timestamps();
    });
}

public function down(): void
{   
    Schema::dropIfExists('profiles');
    Schema::dropIfExists('employees');
}

Run Migration

php artisan migrate

Here,

• profiles.employee_id is a foreign key referencing employees.id.
• With onDelete('cascade'), if you delete an employee, their profile is also deleted automatically.

Model:

Generate a model with Artisan:

php artisan make:model Employee
php artisan make:model Profile

This generates 2 files Employee.php and Profile.php

Employee.php

namespace App\Models;

use App\Models\Profile;
use Illuminate\Database\Eloquent\Model;

class Employee extends Model
{
    protected $fillable = ['name'];

    // Relation: An employee has one profile
    public function profile()
    {
        return $this->hasOne(Profile::class);
    }
}

Profile.php

namespace App\Models;

use App\Models\Employee;
use Illuminate\Database\Eloquent\Model;

class Profile extends Model
{
    protected $fillable = ['employee_id', 'bio'];

    // Relation: A profile belongs to an employee
    public function employee()
    {
        return $this->belongsTo(Employee::class);
    }
}

CRUD Examples for One-to-One

Create:

use App\Models\Employee;

// Method 1
// Create employee
$employee = Employee::create(['name' => 'Watson']);

// Create profile and attach to employee
$employee->profile()->create([
    'bio' => 'Senior Laravel Developer',
]);


// Method 2 Using Eloquent instance
$employee = new Employee();
$employee->name= "John";
$employee->save();

// Create profile and attach to employee
$employee->profile()->create([
    'bio' => 'PHP Developer',
]);

Read

use App\Models\Employee;
use App\Models\Profile;

// Get employee with profile
$employee = Employee::find(1);
echo $employee->profile->bio; // Senior Laravel Developer

// Get profile with employee
$profile = Profile::find(1);
echo $profile->employee->name; // John

Update

use App\Models\Employee;

// Update profile bio of employee
$employee = Employee::find(1);
$employee->profile->update(['bio' => 'Updated Bio']);

Delete

use App\Models\Employee;
use App\Models\Profile;

// Delete employee -> Profile auto deleted (cascade)
Employee::find(1)->delete();

// Or delete profile only not delete employee
Profile::find(2)->delete();

Eager loading (optimizes queries)

use App\Models\Employee;
use App\Models\Profile;

// Get employee with profile
$employee = Employee::with('profile')->find(1);
echo $employee->profile->bio; // Senior Laravel Developer

// Get profile with employee
$profile = Profile::with('employee')->find(1);
echo $profile->employee->name; // John

 Always use with() when fetching related data in bulk.