php mongo Uncaught exception 'MongoDuplicateKeyException' E11000 - php

Question

I am trying to migrate data from mysql to mongo. It adds one record fine to mongo but then on the second record I am getting
Fatal error: Uncaught exception 'MongoDuplicateKeyException' with message 'localhost:27017: E11000 duplicate key error index: app.hospitals.$_id_ dup key: { : ObjectId('558365d7423467484bd63af3') }'
Not sure what I am doing wrong
here is my code
<?php
//echo phpinfo();
$host = "localhost";
$user = "root";
$password = "root";
$database = "database";
// Create connection
$conn = new mysqli($host, $user, $password, $database);
$connection = new MongoClient();
$db = $connection->database;
$collection = $db->hospitals;
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "SELECT * FROM hospitals";
if($result = $conn->query($sql)){
$i=0;
while($row = $result->fetch_assoc()) {
foreach($row as $key=>$value){
$collection->insert($row);
unset($collection->_id);
}
if($i > 3) die;
$i++;
}
}
$conn->close();
?>

Answer 1

using
$collection->save($row);
instead of insert solved the issue. Not sure why though.

Answer 2

Had the same problem, I believe it's a problem with the PHP mongodb driver that it is not generating a new id inside the loop.
The weird part that the first time I called the script it inserted all the documents then the exception popped in the end, then when I dropped the database and called the script again, it only inserted one document before giving the exception.
Anyway I solved after reading this answer by explicitly assigning new id.
In your case, add this before the insert:
$row['_id'] = new MongoId();