$this->getContainer() is returning null in Symfony 3.x for Command

I am working on a project. I have some custom validator which is basically checking some data integrity in my database before saving any new record. So for that check, I need to access the Doctrine entity manager. So below is my code.

CustomValidator.php

<?php
namespace Custom\Validator;

use ....


/**
 * Class CustomValidator
 * @package Custom\Validator
 */
class CustomValidator extends AbstractModel
{
    public function validate()
    {
        //my validation rules
    }
}

This AbstractModel class is basically implementing ContainerAwareInterface like below:

AbstractModel.php

<?php

namespace Custom\Model;

use ....


abstract class AbstractModel implements ContainerAwareInterface
{

     /**
     * @var ContainerInterface
     */
    protected $container;

    public function setContainer(ContainerInterface $container)
    {
        $this->container = $container;
    }

    /**
     * @return ContainerInterface
     */
    protected function getContainer()
    {
        return $this->container;
    }
    /**
     * @return ObjectManager
     */
    public function getObjectManager()
    {
        return $this->getContainer()->get('doctrine')->getManager();
    }

    /**
     * @param $entityClass
     * @return ObjectRepository
     */
    public function getRepository($entityClass)
    {
        return $this->getObjectManager()->getRepository($entityClass);
    }
}

Inside my service.yml file, i defined AbstractModel dependencies like below:

services:

    custom.abstract_model:
        class: Custom\Model\AbstractModel
        abstract: true
        public: true
        calls:
            - [setContainer, ["@service_container"]]

Now, when I am trying to run the validator, I am getting below error:

Call to a member function get() on null

Which indicates this line inside AbstractModel class.

return $this->getContainer()->get('doctrine')->getManager();

Is there anything wrong with my implementation? I tried to search but I failed to find any useful solution.

Update

I believe I didn't explain 10% of the whole scenario and that 10% was the vital part. I was actually using this CustomValidator inside a CustomCommand. That was the main problem, I will explain below if anyone faces a similar problem like me later.

Solution

Firstly, thanks to @Trappar for answering my question. His answer is perfect for the scenario I described earlier. But I did not put whole details and the missing part was the most important part.

So, as I updated my question, I will explain the scenario now.

I had a CustomCommand which looked like this:

<?php

namespace Custom\Command;

class CustomCommand extends Command
{

    protected function configure()
    {
         //my configuration
    }


    protected function execute(InputInterface $input, OutputInterface $output)
    {
            //my custom code

            $oValidator = new CustomValidator();
            $oValidator->validate($aParams);
        }
    }
}

The thing is, in such was I was not getting the container I wanted. So, I went through some extensive research and figured out that for such cases, you have to extend ContainerAwareCommand and not Command. ContainerAwareCommand already extends Command itself and you will also get the container which will be provided by application kernel like below.

$this->container = $application->getKernel()->getContainer();