Laravel, many-to-many relationship to multiple models - php

Question

Looking for a simple way of doing the following in Laravel 5.
Imagine these models and interface
Competition
User
Team
Participant (Interface which User and Team implements)
A competition will have a many-to-many relationship to is participants, which can be either users or teams. So I need the competition_participant pivot table to have the following columns to define the models
competition_id
participant_id
participant_type
But how do I write a relation on the Competition model, so it knows which model it should fetch from the database, and at the same time return a collection of mixed models or of the Interface type?

Answer 1

You had some confusions about which tables should get which columns.
Your participants table needs to be a table for managing the polymorphic relations of users and teams. It receives a particpatable_id and particpatable_type as well as an id and timestamps() at the very minimum.
Then you need an additional table called competition_participant which will manage the belongs to many between competitions and your polymorphic table participants.
This will allow you to relate your participants to your competitions. This way, you can grab all participants by a competition, call the $participant->participatable attribute on it which would return either an App\User or an App\Team depending on what type the participant is.
This is all tested.
Migrations
public function up()
{
Schema::create('competitions', function(Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->timestamps();
});
Schema::create('teams', function(Blueprint $table) {
$table->increments('id');
$table->string('name');
$table->timestamps();
});
Schema::create('participants', function(Blueprint $table) {
$table->increments('id');
$table->integer('participatable_id');
$table->string('participatable_type');
$table->timestamps();
});
Schema::create('competition_participant', function(Blueprint $table) {
$table->integer('competition_id');
$table->integer('participant_id');
});
}
Models
class Competition extends Model
{
public function participants()
{
return $this->belongsToMany(Participant::class);
}
}
class Participant extends Model
{
public function participatable()
{
return $this->morphTo();
}
public function competitions()
{
return $this->belongsToMany(Competition::class);
}
}
class Team extends Model
{
public function participants()
{
return $this->morphMany(Participant::class, 'participatable');
}
}
class User extends Authenticatable
{
public function participants()
{
return $this->morphMany(Participant::class, 'participatable');
}
}
Seeds
public function run()
{
$faker = Faker\Factory::create();
// Seed Users Table
DB::table('users')->delete();
$users = [];
for($i = 0; $i < 100; $i++) {
$users[] = [
'name' => $faker->name,
'email' => $faker->email,
'password' => Hash::make($faker->password),
'created_at' => new DateTime,
'updated_at' => new DateTime
];
}
DB::table('users')->insert($users);
// Seed Teams Table
DB::table('teams')->delete();
$teams = [];
for($i = 0; $i < 20; $i++) {
$teams[] = [
'name' => 'Team ' . ucwords($faker->domainWord),
'created_at' => new DateTime,
'updated_at' => new DateTime
];
}
DB::table('teams')->insert($teams);
// Seed Participants Table
DB::table('participants')->delete();
// Insert some of our users as participants
$users = App\User::limit(20)->orderByRaw('rand()')->get();
foreach($users as $user) {
$user->participants()->create([]);
}
// Insert some of the teams as participants
$teams = App\Team::limit(10)->orderByRaw('rand()')->get();
foreach($teams as $team) {
$team->participants()->create([]);
}
// Seed Competitions Table
DB::table('competitions')->delete();
$competitions = [];
for($i = 0; $i < 10; $i++) {
$competitions[] = [
'name' => $faker->company,
'created_at' => new DateTime,
'updated_at' => new DateTime,
];
}
DB::table('competitions')->insert($competitions);
// Seed Competitions Participants Relationships
DB::table('competition_participant')->delete();
// Sign up each participant to 3 random competitions
$participants = App\Participant::all();
$competitions = App\Competition::all();
foreach($participants as $participant) {
$participant->competitions()->sync($competitions->shuffle()->take(3));
}
}
Usage
$competition = App\Competition::with('participants')->has('participants')->first();
foreach($competition->participants as $participant) {
echo get_class($participant->participatable); // Will output either App\User or App\Team
echo "<br />";
}

Answer 2

This is just a copy paste from the Laravel documentation about many to many polymorphic relationships.
To help you understand better this is the mapping between your models and the models that are on the Laravel documentation:
users == posts
teams == videos
competitions == tags
competitionables == tags
This how you should implement your polymorphic relationship, remember whenever you feel confused just look at the documentation and the mapping between your models and the documention models:
Tables:
users
id - integer
name - string
teams
id - integer
name - string
competitions
id - integer
name - string
competitionables
competition_id - integer
competitionable_id - integer
competitionable_type - string
Model Structure
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class User extends Model
{
/**
* Get all of the Competition for the user.
*/
public function competitions()
{
return $this->morphToMany('App\Competition', 'competitionable');
}
}
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Team extends Model
{
/**
* Get all of the Competition for the Team.
*/
public function competitions()
{
return $this->morphToMany('App\Competition', 'competitionable');
}
}
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Competition extends Model
{
/**
* Get all of the users that are assigned to this Competition.
*/
public function users()
{
return $this->morphedByMany('App\User', 'competitionable');
}
/**
* Get all of the Teams that are assigned to this Competition.
*/
public function teams()
{
return $this->morphedByMany('App\Video', 'competitionable');
}
}
Retrieving The Relationship
$user = App\User::find(1);
foreach ($user->competitions as $competition) {
//
}
or the other way
$competition = App\Competition::find(1);
foreach ($competition->users as $user) {
// do something with your users
}
foreach ($competition->teams as $team) {
// do something with your teams
}