php how to change global to dependency injection - php

Question

I am using global variable in my function and after research I found that is a bad practice in PHP instead of that I should use dependency injection but I have problem when changing global to dependency injection. What problem about my code? Thanks for help.
update.php (global)
<?php
include 'db_data.php';
class robot{
public function robotUpdate($conn3){
public function robotUpdate($conn3){
global $nasa;
global $id;
$r_update="UPDATE robot_heartbeat SET last_process_id =$id WHERE nasa_id=$nasa";
$robot_u=$conn3->query($r_update);
}
main.php
<?php
include 'db_data.php';
include 'db_sat.php';
$sql = "SELECT * FROM satellite1.show_activity ";
$result=$conn1->query($sql); //get data from db 1
while($row = $result->fetch_assoc()) {
$sql2 = "INSERT INTO analysis_data.show_activity SET
show_activity_id='".$row["id"]."',
game_show_id='".$row["game_show_id"]."',
account_id='".$row["account_id"]."',
account_code='".$row["account_code"]."',
login_id='".$row["login_id"]."',
$result=$conn3->prepare($sql2); //copy data from db1 into db2
$result->execute();
}
$robot_u = new robot();
$nasa = '2';
$id = $row["id"];
$robot_u->robotUpdate($conn3);
I tried:
update.php (Dependency injection)
<?php
include 'db_data.php';
class robot{
public function robotUpdate($conn3,$nasa,$id){
public function robotUpdate($conn3){
$r_update="UPDATE robot_heartbeat SET last_process_id =$id WHERE nasa_id=$nasa";
$robot_u=$conn3->query($r_update);
}
**main.php**(dependency injection)
$robot_u = new robot();
$robot_u->robotUpdate($conn3,$nasa,$id); //call function first
$nasa = '2'; //inject value
$id = $row["id"];

Answer 1

the value is injected during the function call:
$robot_u->robotUpdate($conn3,$nasa,$id);
So swap them around:
$robot_u = new robot();
$nasa = '2'; //inject value
$id = $row["id"];
$robot_u->robotUpdate($conn3,$nasa,$id);
That said, I noticed you pass a db connection into the class, you might want to consider, if you re-use the same connection over and over in the class to add a constructor
function __construct( $db_connection ) {
$this->db_connection = $db_connection;
}
And create a new instance of the class and pass the db connection there
$robot_u = new robot( $conn3 );
And every time in that class when you need your db connection, use $this->db_connection instead of passing $conn3
Three are lots of free resources around PHP OOP on the internet, would suggest reading some of them :-)