I have a form for submitting categories. ( new , edit )
<form ... >
<input type="text" name="name" />
<select name="parent_id" >
<option value="0" >Root</option>
<option value="1" >Computer</option>
<option value="..." >...</option>
</select>
</form>
each one of ids in parent_id is a category id in database except for 0, root;
I want to have a validation which says: check parent_id to be a valid id in category table if it is not 0. ( 0 is root and not an id in database )
How can I do that with laravel validation rules.