belongsTo

 belongsTo is generally defined on the model containing the foreign key.

Suppose:

orders
-------
id
user_id
total

Then:

class Order extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

Usage:

$order->user;

Laravel assumes user_id.

You can customize it:

return $this->belongsTo(User::class, 'customer_id');

Important interview point

The relationship direction depends on where the foreign key exists.

users.id
    ↑
orders.user_id

Order belongsTo User, while User hasMany Order.