Laravel Error: Call to a member function format() on string

I had an issue when developing a Laravel 10.x application where I tried to use format() on the deadline_at property.

{{ $project->deadline_at->format('d M Y') }}

It was generating an error "Call to a member function format() on string" as you can see on the attached screenshot.

I have added the following attribute to my Laravel Eloquent Model:

protected $dates = [
    'start_at',
    'deadline_at',
];

So in order to solve this error in Laravel 10.x is to not use the protected $dates, instead use protected casts where we added the property that should be mutated to dates.

/**
* The attributes that should be cast.
*
* @var array
*/
protected $casts = [
    'deadline_at' => 'datetime',
];

If your Laravel application version is below 10.x, such as Laravel 9.x, you can still use the protected $dates.

protected $dates = [
    'start_at',
    'deadline_at',
];

Reference:

• Laravel Eloquent 10.x Mutators & Casting
• Laravel Eloquent 9.x Mutators & Casting