Migration nullable field causing issues - php

Question

I have created a migration called 'create_modules_table' see code below.
public function up()
{
Schema::create('modules', function (Blueprint $table) {
$table->id();
$table->unsignedBigInteger('course_id')->nullable();
$table->foreign('course_id')->references('id')->on('courses');
$table->string('title');
$table->timestamps();
});
}
I have added a FK 'course_id'. Without 'nullable' i faced an error relating to 'course_id' not having a default value. So i added 'nullable'. However now it is throwing me further problems, when i create a new module and select the course to attach to the module, the field in the DB is null (despite selecting an existing course from my form). I have added an image for context. Can anyone tell me where i am going wrong? I'm not sure how to go about fixing this.
Module.php
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Module extends Model
{
protected $fillable = [
'title', 'course_id', 'created_at', 'updated_at',
];
public function course()
{
return $this->belongsTo(Course::class, 'course_id');
}
}
ModulesController;
<?php
namespace App\Http\Controllers\Admin;
use App\Module;
use App\Course;
use App\Http\Controllers\Controller;
use Illuminate\Http\Request;
class ModulesController extends Controller
{
public function index(Request $request)
{
$modules = new module();
if ($request->input('course_id')) {
$modules = $modules->where('course_id', $request->input('course_id'));
}
$modules = $modules->all();
return view('admin.module.index', compact('modules'));
}
public function create()
{
$courses = Course::all()->pluck('title', 'id');
return view('admin.module.create', compact('courses'));
}
public function store(Request $request)
{
$module = Module::create($request->all());
return redirect()->route('admin.modules.index', ['course_id' => $request->id]); //redirects to correct route by adding course_id in parameter
}
}
create.blade.php;
#extends('layouts.app')
#section('content')
<div class="row justify-content-center">
<div class="col-md-8">
<div class="card">
<div class="card-header">Create Module</div>
<div class="card-body">
<form method="POST" action="{{ route('admin.modules.store') }}" enctype="multipart/form-data">
#csrf
<div class="form-group">
<label class="required" for="name">Module Title</label>
<input class="form-control" type="text" name="title" id="id" required>
#if($errors->has('name'))
<div class="invalid-feedback">
{{ $errors->first('name') }}
</div>
#endif
</div>
<div class="form-group">
{!! Form::label('Courses', 'Course', ['class' => 'control-label']) !!}
{!! Form::select('Course[]', $courses, Request::get('Course'), ['class' => 'form-control select2', 'multiple' => 'multiple']) !!}
</div>
<div class="form-group">
<button class="btn btn-danger" type="submit">
Save
</button>
</div>
</div>
</form>
</div>
</div>
#endsection
index.blade.php;
#extends('layouts.app')
#section('content')
<div class="container">
<div class="row justify-content-center">
<div class="col-md-8">
<p>
<button type="button" class="btn btn-success">Create Module</button>
</p>
<div class="card">
<div class="card-header">Modules</div>
<div class="card-body">
<div class="table-responsive">
<table class="table">
<thead>
<tr>
<th>ID</th>
<th>Module Title</th>
<th>Course Title</th>
<th>Instructor</th>
<th></th>
<th></th>
<th></th>
</tr>
</thead>
<tbody>
#foreach($modules as $key => $module)
<tr>
<th scope="row">{{ $module->id }}</th>
<td>{{ $module->title }}</td>
<td>{{ $module->course->title ?? ''}}</td>
</tr>
#endforeach
</tbody>
</table>
</div>
</div>
</div>
</div>
#endsection
I would like to add there is no error, the DB is simply not displaying an input.. for some reason. Any help is kindly appreciated.

Answer 1

In your form there is no field named course_id, instead you've a field with name Course[] which is a multi-select, so in your store method when you are using Module::create($request->all()); there is no field matching in your $fillable array in the Module model, so you need to map fields manually and also, since you are using an array (because multi-select produces array), you need to use single element from the array to create a relation.
So, one easy approach could be ():
Module::create([
'title' => $request->input('title'),
'course_id' => reset($request->input('course')) // get the first item from array
]);
I think your are missing something, you should not use a multi-select for a foreign key unless you've a many-to-many relation and in that case you'll create/attach multiple related entries in a pivot table.