Can't get variable from Laravel ORM relations - php

Question

I want to get "$invoice->form->form" parameter here because i want to use it in view. When i am using dd($invoice->form); than gets null. Invoice and form are other tables and models but are connected with laravel relationship and foreign keys in migrations.
public function show(Invoice $invoice)
{
dd($invoice->form);
return view('invoices.show',compact('invoice'));
}
This is begining of invoice controller file:
namespace App\Http\Controllers;
use Kyslik\ColumnSortable\Sortable;
use App\Invoice;
use Illuminate\Http\Request;
use App\User;
use App\Proform;
use App\Form;
use App\Currency;
use DB;
Here is invoice model
<?php
namespace App;
use Kyslik\ColumnSortable\Sortable;
use Illuminate\Database\Eloquent\Model;
use Illuminate\Database\Eloquent\SoftDeletes;
class Invoice extends Model
{
/**
* The attributes that are mass assignable.
*
* #var array
*/
use SoftDeletes;
use Sortable;
protected $table = 'invoices';
protected $fillable = [
'invoicenumber', 'invoicedate', 'id', 'selldate', 'user_id', 'paymentmethod',
'paymentdate', 'status', 'comments', 'city', 'paid', 'autonumber', 'automonth', 'autoyear', 'name',
'PKWIU', 'quantity', 'unit', 'netunit', 'nettotal',
'VATrate', 'grossunit', 'grosstotal', 'form_id', 'currency_id',
];
public $sortable = [ 'invoicenumber', 'invoicedate', 'id', 'selldate', 'user_id', 'paymentmethod',
'paymentdate', 'status', 'comments', 'city', 'paid', 'autonumber', 'automonth', 'autoyear', 'name',
'PKWIU', 'quantity', 'unit', 'netunit', 'nettotal',
'VATrate', 'grossunit', 'grosstotal', 'form_id', 'currency_id',
];
protected $dates = ['deleted_at'];
public $primaryKey = 'id';
public function user()
{
return $this->belongsTo('App\User');
}
public function form()
{
return $this->hasOne('App\Form');
}
public function currency()
{
return $this->hasOne('App\Currency');
}
public function proform()
{
return $this->belongsTo('App\Proform');
}
}
Here is form model:
<?php
namespace App;
use Illuminate\Database\Eloquent\Model;
class Form extends Model
{
//
protected $fillable = [
'id', 'form',
];
public function invoice()
{
return $this->belongsTo('App\Invoice');
}
public function proform()
{
return $this->belongsTo('App\Proform');
}
}

Answer 1

Because you aren't loading the relation.
On your controller you should query like: $invoice = Invoice::with('form')->find($invoice_id); and return it to the view like: return view('invoices.show', [ 'invoice' => $invoice->form ]);