Magento 2 : Can not add method/class in __construct()

Question

I have a collection.php file. I am adding some function into that which calls other models.As per Magento 2 first we have to add object managerger interface. And then we can call other model.like below :

$this->_objectManger('\Namespace\Module\Model\Customfile')->functionName();

To use $this->_objectManger we have to define in __Construct first. Now I am doing same thing in __Construct method of Collection.php file. But it is not working and creating issues.

Please check code : Collection.php

<?php
namespace \Namespace\Module\Model\ResourceModel\Testfile;

class Collection extends \Magento\Framework\Model\ResourceModel\Db\Collection\AbstractCollection
{

 public function __construct(
    **\Magento\Framework\ObjectManagerInterface $objectManager,** 
    \Magento\Framework\Data\Collection\EntityFactory $entityFactory,
    \Psr\Log\LoggerInterface $logger,
    \Magento\Framework\Data\Collection\Db\FetchStrategyInterface $fetchStrategy,
    \Magento\Framework\Event\ManagerInterface $eventManager,
    \Magento\Catalog\Model\ResourceModel\Product\Option\Value\CollectionFactory $optionValueCollectionFactory,
    \Magento\Store\Model\StoreManagerInterface $storeManager,
    \Magento\Framework\DB\Adapter\AdapterInterface $connection = null,
    \Magento\Framework\Model\ResourceModel\Db\AbstractDb $resource = null
) {
    $this->_optionValueCollectionFactory = $optionValueCollectionFactory;
    $this->_storeManager = $storeManager;
    parent::__construct($entityFactory, $logger, $fetchStrategy, $eventManager, $connection, $resource);
    $this->logger = $logger; 
    $this->_objectManager = $objectManager;
 }

How to add extra classes in this ? Please explain where I am wrong and why.

Answer 1

Please explain where I am wrong and why.

You should not require the object manager itself as dependency in the constructor, instead require the object you need directly:

public function __construct(
    ...,
    \Namespace\Module\Model\Customfile $customfile
) {
    ...
    $this->customfile = $customfile;
}

Then use it like this:

$this->customfile->functionName();

This will use a shared instance of the Customfile model (like a singleton in Magento 1). If you need a new instance every time, you can use the automatically generated factory.

With Factory:

public function __construct(
    ...,
    \Namespace\Module\Model\CustomfileFactory $customfileFactory
) {
    ...
    $this->customfileFactory = $customfileFactory;
}

Usage:

$customfile = $this->customFileFactory->create();
$customfile->functionName();