Validate when passing individual data using JSON.stringify - laravel

Question

Before passing the data to Controller, the data is being added :
formData.push({"name":"channels","value":JSON.stringify(channels)});
Cause of this even when no data is present, its passed like
'channels' => '[]'
Now the issue is when I try to validate this in validator, I cannot use
'channels' =>'required',
'channels.*' =>'required|exists:channels,id',
How do validate the above data? Don't want to convert the format as its a working system. Any suggestions are appreciated. Thanks.
Updated for Request All Params:
'_token' => 'DjqgmNab0o3ifrVrSvHh6dM5vxLP7tZDc47pq05r',
'startdate' => '05 Sep 2018',
'years' => NULL,
'months' => NULL,
'enddate' => NULL,
'addChannel' => NULL,
'offerRuns' => 'UL',
'numberOfRuns' => NULL,
'limitPeriod' => 'FP',
'licenseAudioTrack' => '1',
'amount' => NULL,
'include_materials_costs' => '1',
'include_withholding_taxes' => '1',
'paymentTermsType' => 'US',
'termsAndConditionDescription' => NULL,
'document_s3_url' => NULL,
'file' => NULL,
'fileSize' => NULL,
'materialSpecificationDescription' => NULL,
'note' => NULL,
'countries' => '[]',
'platforms' => '["1","2","3","4","5","6","7","8","9"]',
'platforms-exclusive' => '[]',
'platforms-non-exclusive' => '[]',
'platforms-holdback' => '[]',
'channels' => '[]',
'languages' => '[["56","AL",1,"seller"]]',
'currencySelectedTerm' => 'EP',
'currencyId' => '1',
'paymentTerms' => '[]'

Answer 1

Check the present validation rule. It states:
present
The field under validation must be present in the input data but can
be empty.
Also look into sometimes rule:
In some situations, you may wish to run validation checks against a
field only if that field is present in the input array. To quickly
accomplish this, add the sometimes rule to your rule list
https://laravel.com/docs/5.7/validation#conditionally-adding-rules

Answer 2

As I understood channels is passed as JSON string & required validator is not working because it is not an empty string.
You can create a custom validator to validate empty JSON string & use it.
<?php
namespace App\Rules;
use Illuminate\Contracts\Validation\Rule;
class JsonRequired implements Rule
{
/**
* Determine if the validation rule passes.
*
* #param string $attribute
* #param mixed $value
* #return bool
*/
public function passes($attribute, $value)
{
return ! empty(json_decode($value, true));
}
/**
* Get the validation error message.
*
* #return string
*/
public function message()
{
return 'The :attribute is required.';
}
}
And use it as 'channels' =>'new JsonRequired'.
If you only need once throughout your application, you may use a Closure instead of a rule object.
Laravel custom validation

Answer 3

You can use json_decode for data first and then apply validations
public function store(Request $request)
{
$request_data = $request->all();
foreach($request_data as $key=>$value)
{
$request_data[$key] = json_decode($value);
}
// And then pass data in validator rules
$rules = [
// All rules here
];
$validator = Validator::make($request_data, $rules);
// other code
}