PHP - Dependency Injection Via Setter Method

I just updated a site as follows:

cd /var/www/concrete5
composer update

Among other changes, the following were made (more on this later):

  - Updating concrete5/core (8.5.2 => 8.5.4): Downloading (100%)
  - Updating doctrine/collections (1.6.4 => 1.6.5): Downloading (100%)
  - Updating doctrine/lexer (1.2.0 => 1.2.1): Downloading (100%)
  - Updating doctrine/inflector (1.3.1 => 1.4.3): Downloading (100%)
  - Updating doctrine/cache (1.10.0 => 1.10.1): Downloading (100%)
  - Updating doctrine/annotations (1.10.2 => 1.10.3): Downloading (100%)
  - Updating doctrine/common (2.12.0 => 2.13.3): Downloading (100%)
  - Updating doctrine/instantiator (1.3.0 => 1.3.1): Downloading (100%)
  - Updating doctrine/orm (v2.7.2 => v2.7.3): Downloading (100%)

When accessing the site, I now have the following error:

errno: 150 "Foreign key constraint is incorrectly formed

I expected I should have first used concrete5's update script, but too late for that.  So, then I changed composer.json require concrete5/core from ^8.5 to 8.5.2 hoping to return to the previous state.

Concreete5 was downgraded as desired, but now I get the following error:

Class 'Doctrine\Common\Persistence\Mapping\Driver\MappingDriverChain' not found

On another concrete5 site which still works, I have the following two files, however, on the broken one I only have the second:

So, now I will attempt to downgrade doctrine from 2.7.3 to 2.7.2.  The base composer.json file has no reference to Doctrine, but there are two other related composer files:

vendor/concrete5/doctrine-xml/composer.json

{
    "name": "concrete5/doctrine-xml",
    "description": "Define database structure via XML using Doctrine data types",
    "keywords": [
        "doctrine",
        "xml",
        "structure",
        "database",
        "schema"
    ],
    "homepage": "https://github.com/concrete5/doctrine-xml",
    "license": "MIT",
    "autoload": {
        "psr-4": {
            "DoctrineXml\\": "src/"
        }
    },
    "require": {
        "php": ">=5.3"
    },
    "require-dev": {
        "doctrine/dbal": "2.5.*"
    }
}

vendor/concrete5/dependency-patches/composer.json

{
    "type":"library",
    "license":"MIT",
    "name":"concrete5/dependency-patches",
    "description":"Patches required for concrete5 dependencies",
    "homepage":"https://github.com/concrete5/dependency-patches",
    "authors":[
        {
            "name":"Michele Locati",
            "email":"michele@locati.it",
            "role":"author",
            "homepage":"https://mlocati.github.io"
        }
    ],
    "require":{
        "mlocati/composer-patcher": "^1.0.0"
    },
    "extra":{
        "patches": {
            "doctrine/annotations:1.2.7": {
                "Fix access array offset on value of type null": "doctrine/annotations/access-array-offset-on-null.patch"
            },
            "doctrine/orm:2.5.14": {
                "Fix UnitOfWork::createEntity()": "doctrine/orm/UnitOfWork-createEntity-continue.patch"
            },
            "zendframework/zend-stdlib:2.7.7": {
                "Fix ArrayObject::unserialize()": "zendframework/zend-stdlib/ArrayObject-unserialize-continue.patch"
            },
            "sunra/php-simple-html-dom-parser:1.5.2": {
                "Fix minus in regular expressions": "sunra/php-simple-html-dom-parser/minus-in-regular-expressions.patch"
            },
            "phpunit/phpunit:4.8.36": {
                "Avoid each() in Getopt": "phpunit/phpunit/Getopt-each.patch"
            },
            "tedivm/jshrink:1.1.0": {
                "Fix continue switch in Minifier": "tedivm/jshrink/fix-minifier-loop.patch",
                "Update to upstream version 1.3.2": "tedivm/jshrink/update-upstream-1.3.2.patch"
            },
            "zendframework/zend-code:2.6.3": {
                "Fix continue switch in FileGenerator and MethodReflection": "zendframework/zend-code/switch-continue.patch"
            },
            "zendframework/zend-http:2.6.0": {
                "Remove support for the X-Original-Url and X-Rewrite-Url headers": "zendframework/zend-http/no-x-original-url-x-rewrite.patch"
            },
            "zendframework/zend-mail:2.7.3": {
                "Fix idn_to_ascii deprecation warning": "zendframework/zend-mail/fix-idn_to_ascii-deprecation-warning.patch"
            },
            "zendframework/zend-validator:2.8.2": {
                "Fix idn_to_ascii/idn_to_utf8 deprecation warning": "zendframework/zend-validator/fix-idn_to_-deprecation-warning.patch"
            }
        }
    }
}

Neither seem to be applicable, but the doctrine version has to be specified somewhere.   How does composer determine which version and how can I downgrade the dependency package?  Thanks

PS.  As a hack solution, I replaced the entire vendor/doctrine directory from one from another site, and have things working.  Still, want to know how to do this right.

My script has 3 classes (that are relevant to this discussion): DB, User and Validate. They are all in independent files and loaded automatically, when required, by an autoloader.
Both the User class and the Validate class have a private variable $_db which is instantiated by their class constructor: $this->_db = DB::getInstance();
At the top of the script I declare new instances: $user = new User(); and $validate = new Validate();
I then call a method in $user: $found = $user->findInUsers ( .... )
From within the findInUsers method I then want to call the query method in the DB class. My problem is that I can't find a way to do this that works.
I have tried $this->_db->query( ... ), $_db->query( ... ), but neither works.

The error messages I am getting a
An error occurred in script '/srv/http/classes/User.php' on line 42: Undefined variable $_db
Uncaught Error: Call to a member function query() on null in /srv/http/classes/User.php:42

Any pointers as to what I am doing wrong, or what I should be doing, would be most welcome.

Based on the comments on my previous question, took some tutorials on how to avoid injections on query. Does the code below prevents against it in any way.? Secondly, can you recommend a good article that writes well in how to secure input data by users. Please be kind with your comments.😉😉. Thankks in advance.

The code works fine.
 

<?php 

include 'db.php';

error_reporting(E_ALL | E_WARNING | E_NOTICE);

ini_set('display_errors', TRUE);

 if(isset($_POST['submit']))

 {
    
 $username = $_POST['username']; 
$password =  ($_POST['password']); 

$sql = "SELECT * FROM customer WHERE username = ?";
$stmt = $connection->prepare($sql); 
$stmt->bind_param('s', $username);
$stmt->execute();
$result = $stmt->get_result();
$count =  $result->num_rows;
   if($count == 1) 
                         {
while ($row = $result->fetch_assoc())
 {
    if ($row['status'] == 'blocked')

 {

 echo'your account is suspended'


   session_destroy();

   exit();

  }

 else if($row['status'] == 'active')
{

if($username !== $row['username']) 

 { 
echo '<script>swal.fire("ERROR!!", " Username is not correct. Check Again", "error");</script>';
} 
if($password !== $row['password']) 
{
  echo'<script>swal.fire("ERROR!!!", "Your Password is Incorrect. Check Again.", "error");</script>';       
}
if($username == $row['username'] && $password == $row['password']) 
{ 
header('Location:cpanel/');
else
{
}
}//if count
}//while loop
}//submit
?>