Прием Json в качестве тела для последующего разбора и запроса типа UPDATE mysql

$exchangeRates = json_decode($json, true);
foreach($exchangeRates['rates'] as $key => $value) {
if($value) {
    mysqli_query($mysql,"UPDATE currencies SET dblRateCAD = '".$value."' WHERE strCode = '". $key ."' LIMIT 1");
    }
}

$json_arr = json_decode('{"product_code":"1","product_name":"велосипед","product_price":"14000"}', true);
$filed = array_keys($json_arr);
$value = array_values($json_arr);
 
echo "UPDATE `Products` SET `$filed[1]`='$value[1]',`$filed[2]`='$value[2]' WHERE `$filed[0]`='$value[0]'";

 SET `$filed[1]`='$value[1]',`$filed[2]`='$value[2]'

function makeMysqlQuery($json,$tableName,$fieldCrit)
{
$keys=json_decode($json,true);
$criteria=null;// переменная для склейки условия после WHERE
$setBody=null; //переменная для склейки  после SET
foreach($keys as $fieldKey=>$fieldData){
    
  if ($fieldKey==$fieldCrit){
  $criteria= " WHERE ".$fieldCrit."=".$fieldData;  
  } else {
   $setBody ="{$fieldKey}={$fieldData}".",".$setBody;   
   }
} 
$query = "UPDATE ".$tableName." SET ".rtrim($setBody,",").$criteria;
echo $query;   
}

$json = '{"product_code":"1","product_name":"велосипед","product_price":"14000"}';
$tableName="Products";
$fieldCrit="product_code";
 
makeMysqlQuery($json,$tableName,$fieldCrit);

$myVar = '"собака"';
//или
$myVar = "\"собака\"";

<?php
$data = json_decode('{"product_code":"1","product_name":"велосипед","product_price":"14000"}');
 
$mysqli = new mysqli("example.com", "user", "password", "database");
$stmt = $mysqli->prepare('UPDATE Products SET product_name=?, product_price=? WHERE product_code=?');
$stmt->bind_param($data['product_name'], 1);
$stmt->bind_param($data['product_price'], 2);
$stmt->bind_param($data['product_code'], 3);
$stmt->execute();

<?php
abstract class Model {
    protected static $table = null;
    protected static $fields = null;
    protected static $_sql_update = null;
 
    public static function init() {
        $list = array('UPDATE', static::$table, 'SET');
        $values = array();
        for ($i = 1; $i < count(static::$fields); $i++) {
            $values[] = static::$fields[$i] . '=?';
        }
        $list[] = implode(', ', $values);
        $list[] = 'WHERE';
        $list[] = static::$fields[0] . '=?';        
        self::$_sql_update = implode(' ', $list);
        # echo self::$_sql_update;
    }
 
    public function update($mysqli, $data) {
        $stmt = $mysqli->prepare(self::$_sql_update);
        for ($i = 1; $i < count(static::$fields); $i++) {
            $stmt->bind_param($data[static::$fields[$i]], $i);
        }
        $stmt->bind_param($data[static::$fields[0]], count(static::$fields) - 1);
        $stmt->execute();
    }
}
 
class Product extends Model {
    protected static $table = 'Products';
    protected static $fields = array('product_code', 'product_name', 'product_price');
}
Product::init();
 
#$mysqli = new mysqli("example.com", "user", "password", "database");
$data = json_decode('{"product_code":"1","product_name":"велосипед","product_price":"14000"}');
 
$p = new Product();
$p->update($mysqli, $data);

function makeMysqlQuery($json,$tableName,$fieldCrit)