Get relationship data from eloquent builder laravel 7 - php

Question

I wanna filter my table data. I have a table for states, one for cities and one for students.
states(id, name)
cities(id, name, state_id)
students(id, first_name, last_name, city_id)
When I wanna filter data with eloquent builder how can I access relationships for handle state filter.
<?php
namespace App\StudentSearch\Filters;
use Illuminate\Database\Eloquent\Builder;
class StateId implements Filter
{
/**
* #inheritDoc
*/
public static function apply(Builder $builder, $value)
{
// something like this
return $builder->where('state_id', $value);
}
}
StudentSearch.php
<?php
namespace App\StudentSearch;
use App\Student;
use Illuminate\Http\Request;
use Illuminate\Database\Eloquent\Builder;
use Illuminate\Support\Str;
class StudentSearch
{
public static function apply(Request $filters)
{
$query = static::applyDecoratorsFromRequest($filters, (new Student)->newQuery());
return static::getResults($query);
}
private static function applyDecoratorsFromRequest(Request $request, Builder $query)
{
foreach ($request->all() as $filterName => $value) {
$decorator = static::createFilterDecorator($filterName);
if (static::isValidDecorator($decorator)) {
$query = $decorator::apply($query, $value);
}
}
return $query;
}
private static function createFilterDecorator($name)
{
return __NAMESPACE__ . '\\Filters\\' . Str::studly($name);
}
private static function isValidDecorator($decorator)
{
return class_exists($decorator);
}
private static function getResults(Builder $query)
{
return $query->get();
}
}
Note that relations between tables is completely defined in models.

Answer 1

I found the solution.
We can do this with eloquent builder:
$builder->whereHas('relationName', function($query) use($value) {
$query->where('state_id', $value);
});
Link to source