Many To Many

What is Many To Many?

A Many To Many relationship occurs when a record in one table can relate to many records in another table and vice versa.

👉 Example:

• A Student can enroll in many Courses.
• A Course can have many Students.

This relationship requires a pivot table (in Laravel usually named course_student).

Students ↔ Courses  

Migration:

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

php artisan make:migration create_onetomany_manytoone_tables

Migration File

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

    Schema::create('courses', function (Blueprint $table) {
        $table->id();
        $table->string('title');
        $table->timestamps();
    });

    // Pivot table
    Schema::create('course_student', function (Blueprint $table) {
        $table->id();
        $table->foreignId('student_id')->constrained()->onDelete('cascade');
        $table->foreignId('course_id')->constrained()->onDelete('cascade');
        $table->timestamps();
    });
}

public function down(): void
{
    Schema::dropIfExists('course_student');
    Schema::dropIfExists('courses');
    Schema::dropIfExists('students');
}

Run Migration

php artisan migrate

• course_student.student_id is a foreign key referencing students.id.
• course_student.course_id is a foreign key referencing courses.id.

Model:

Generate a model with Artisan:

php artisan make:model Student
php artisan make:model Course

This generates 2 files Student.php and Course.php

Student.php

namespace App\Models;

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

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

    public function courses() {
        return $this->belongsToMany(Course::class, 'course_student');
    }
}

Course.php

namespace App\Models;

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

class Course extends Model
{
    protected $fillable = ['title'];

    public function students() {
        return $this->belongsToMany(Student::class, 'course_student');
    }
}

CRUD Examples

Create (Attach Student to Course)

use App\Models\Course;
use App\Models\Student;

// Create Student
$student = Student::create(['name' => 'John']);

// Create Course
$course = Course::create(['title' => 'Java']);

// Attach
$student->courses()->attach($course->id);

Read (Get Related Data)

use App\Models\Student;
use App\Models\Course;

// Get all courses of a student
$student = Student::find(1);
foreach ($student->courses as $course) {
  echo $course->title;
}

// Get all students of a course
$course = Course::find(1);
foreach ($course->students as $student) {
  echo $student->name;
}

Update (Sync Courses for a Student)

use App\Models\Student;
use App\Models\Course;

// Replace student’s courses with new ones
// Create Course
$course = Course::create(['title' => 'Laravel']);
$course = Course::create(['title' => 'PHP']);
$student = Student::find(1);
$student->courses()->sync([1, 2, 3]); // keeps only these

Delete (Detach Student from Course)

use App\Models\Student;

$student = Student::find(1);
$student->courses()->detach(2); // remove course id 2 only

// or remove all courses ids in course_student table
$student->courses()->detach();

// Delete Student (will cascade course_student also if set cascade)
$student->delete()


Similarly Courses
$course = Course::find(1);
$course->students()->detach(2); // remove student id 2 only

// or remove all students ids in course_student table
$course->students()->detach();

// Delete Course (will cascade course_student also if set cascade)
$course->delete()

Eager loading (optimizes queries)

use App\Models\Student;
use App\Models\Course;

// Get all courses of a student
$student = Student::with('courses')->find(1);
foreach ($student->courses as $course) {
  echo $course->title;
}

// Get all students of a course
$course = Course::with('students')->find(1);
foreach ($course->students as $student) {
  echo $student->name;
}

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