HasJsonFields.php

<?php

namespace App\Traits;

trait HasJsonFields
{
    public function newFromBuilder($attributes = [], $connection = null)
    {
        $model = parent::newFromBuilder($attributes, $connection);

        $model->addHintedAttributes();

        return $model;
    }

    public function addHintedAttributes()
    {
        foreach($this->hintedAttributes as $col => $structure) {
            $attrs = json_decode($this->attributes[$col]);
            $obj = (object)$structure;

            if(is_object($obj)) {
                foreach($obj as $key => $value) {
                    if(!isset($attrs->$key)) {
                        $attrs->$key = $value;
                    }
                }
                $this->attributes[$col] = json_encode($attrs);
            }
        }
    }
}

MyModel.php

<?php

namespace App;

use Illuminate\Database\Eloquent\Model;
use App\Traits\HasJsonFields;

class MyModel extends Model
{
    use HasJsonFields;

    public $jsonColumns = [
        'user_details',
        'details'
    ];

    public $hintedAttributes = [
        'user_details' => [
            'first_name' => '',
            'last_name' => '',
            'email' => '',
            'phone' => ''
        ],
        'details' => [
            'question' => '',
            'answer' => ''
        ]
    ];
}

I usually do

$casts = [
    'options' => 'array,
];

The $casts makes sure that when Eloquent pulls it from the DB it does json_decode() and then json_encode when it saves it.
And then have a function to set/unset options

public function setOption($key, $value)
{
    $options = $this->options;
    $options[$key] = $value;
    $this->options = $options;
    $this->save();
    return $this;
}

public function unsetOption($key)
{
    $options = $this->options;
    unset($options[$key]);
    $this->options = $options;
    $this->save();
    return $this;
}

Then if there's a special option I want, like the order of items, I'll add an accessor and append it to the model.

/**
 * Fetches the order, returns 1 if not set.
 */
public function getOrderAttribute() 
{
    return $this->options['order'] ?? 1;
}

$appends = [
    'order',
];

This is so I can grab the order by just doing $model->order instead of $model->options['order']