Eloquent Relationship with examples in Laravel

 
Defining Relationship:

1. One to One relationship
2. One to Many relationships
3. Many to One relationship
4. Many to Many Relationship

Consider, User.php, and Post.php model. To find a single record according to a user, we can implement one to one relationships between two entities.

One to One Relationship

So, in the User.php model add the code to get permission to access the posts table by the user.

/* * One to one relationship method to get users single post 

*/

public function post(){     

    return $this->hasOne('App\Post'); 

}

before that add an extra column to the 2020_08_11_053014_create_posts_table migration to refer the user identity. Then looks like

public function up(){ 

Schema::create('posts', function (Blueprint $table) { 

    $table->id();         

    $table->string('title');         

    $table->integer('user_id'); // new column added here         

    $table->string('body');         

    $table->boolean('is_admin')->default(0);         

    $table->timestamps();     

 }); 

}

Now again migrate, by running this command

php artisan migrate:fresh

Insert some data to the posts table and users table. then,

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In web.php file create a route to fetch a single record.

Route::get('/user/{id}/post',function ($id){    

    return User::find($id)->post; 

});

Find the owner of the post

To find the owner of the post makes Inverse one to one relationship. 

Add the code to the Post.php model

/* * Inverse relationship to get User data */ 

public function user(){     

     return $this->belongsTo('App\User'); 

}

Create a route in the web.php file

Route::get('/post/{id}/user',function ($id){     

return Post::find($id)->user; 

});

Output:

{"id":1,"name":"Jewel Chowdhury","email":"jewelcse045@gmail.com","email_verified_at":null, 


"created_at":"2020-08-12T16:12:04.000000Z", 


"updated_at":"2020-08-12T16:12:04.000000Z"}

One to Many relationships

It means that a single user has more than one post. We have to fetch all records. So, add the code in the User.php model.

User.php

/* * One to Many relationship method to get users all post */
public function posts(){     

    return $this->hasMany('App\Post');

}

Create a route

/* * One to Many relationship */
Route::get('/user/{id}/posts',function ($id){     

     return User::find($id)->posts; 

});

Many to Many relationships

In this scenario, to relate many to many relationships between two tables there needs an extra table. This table is called a pivot table. There is no need to make a model for this pivot table. The only pivot table is used for a database to store the reference. Pivot is a lookup table.

So, in this situation, We want to make user roles table, role_user table. Users different role store in the roles table. Multiple users can have the same role. And this is why the pivot table comes here. role_user refers to the pivot table.

Firstly, create a Role model by running this command

php artisan make:model Role -m

It creates a Role.php model and also creates a migration file.

Add this code in the roles migration table

public function up(){ 

Schema::create('roles', function (Blueprint $table) {         

    $table->id();         

    $table->string('name');         

    $table->timestamps();     

 }); 

}

And we have to create a pivot table named as role_user by running this command

php artisan make:migration create_users_role_table --create=role_user

Add this code in the role_user migration file

public function up(){ 

Schema::create('role_user', function (Blueprint $table) {         

    $table->id();         

    $table->integer('user_id'); // user id         

    $table->integer('role_id'); // role id         

    $table->timestamps();     

}); 

}

Now, let's create our route

/* * Many to Many relationship */
Route::get('/user/{id}/role',function ($id){     

    $user = User::find($id);     

   //return $user->roles; 

    foreach ($user->roles as $role){         

         echo $role->name."<br>";     

    } 

});

Output:

Adminstrative
Contributor

Find the owner of the role

Route::get('/role/{id}/user',function ($id){     

     $role = Role::find($id);    

     // return $role->users; 

      foreach ($role->users as $user){         

      echo $user->name;     

    } 

});

Output:

Jewel Chowdhury