Magento2

It's very recommanded to delete unused carts after you finish the upgrade using these queries all customers carts that are not converted to order will be deleted 

select * 
FROM `quote_address`
WHERE `customer_address_id` IS NULL AND `firstname` IS NULL AND `lastname` IS NULL and quote_id in (SELECT entity_id FROM `quote` where is_active= 1)

select *    from quote where entity_id not in (select quote_id from quote_address)

Some time you will have the below error after you move Magento2 from server to another server with different PHP version or even with the same PHP version , now what is the first solution we can do 

mostly this library will be missed 

php-sodium

So we need to install it , below is some command we can do to install it on Centos

Most programmer need to change sometime the password of one customer programmatically, in this wiki I will give you a code to change the password programmatically

ln -s /my/real/path/to/media /my/path/to/magento/media

I have looked at almost 100 articles to know how Magento format the URL without any success and finally I found it and it was really so easy , here is the quick way to see it using object manager

Note: please consider to use the dependency injection

$_productloader = $objectManager->get('\Magento\Catalog\Model\ProductFactory');
$product =  $_productloader->create()->load(1);


echo  $product->formatUrlKey({Your text here});

in this way Magento will give you the correct URL which will be used 

How do you add translation for extensions in Magento2?

Then generate the dictionary with magento shell tool; from :

php bin/magento i18n:collect-phrases -o app/code/{Vendor}/{Module}/i18n/en_US.csv app/code/{Vendor}/{Module}/

do not forget to replace {Vendor} and {Module} with your correct information 

the easy way is to go to this file 

\vendor\magento\framework\Event\Manager.php

then go to this function dispatch

you can now user this 

foreach ($this->_eventConfig->getObservers($eventName) as $observerConfig) {
    if ($eventName == "catalog_product_save_after") {
         $all_observers = print_r($observerConfig, true);
    }
}

The most frequent question, asked by Magento users, is correct permissions. They can differ, whether you run your store in one-user mode, or many-user, and also can be different for different modes.

Single user mode

One-user mode is the simplest case. In this case user shall belong to group, which own Magento system and also runs web-server. For them the following rules apply:

The best easy way is to simulate the directory path, so lets assume you will need to fix the comparison page after you upgrade to Magento 2.3.5-p2

Filename: vendor/magento/module-catalog/Helper/Output.php

we need to replace this line 

- if (preg_match($pattern, $attributeHtml)) {

with this line 

+ if (preg_match($pattern, (string) $attributeHtml)) {

Now create those directories vendor/magento/module-catalog/Helper

To change the HasSpecialPrice value you need to create a new module then after that you can add this code to the etc/di.xml