如何替换具有 BSON UTCDateTime 的 MongoDB 记录？

Question

I'm using MongoDB version 3.4.17, accessed via PHP (MongoDB PHP API version 1.4). When the server writes a JSON document to the database, it first adds a timestamp field like so:

$record['date_modified'] = new MongoDB\BSON\UTCDateTime();

When reloading this record, which is serialized into a JSON, used by JavaScript, then passed back to the server to be saved with collection->replaceOne(), I get this error:

invalid argument for replace: keys cannot begin with "$": "$date""

The JavaScript console shows the date as an object with multiple levels of child objects:

date_modified:
   $date:
       $numberLong: "1572318771000"

Questions:

1. What should I be doing differently so I can save the JSON back to the database without it throwing the error it does for 'keys cannot begin with "$"?

2. It would be handy for JavaScript to have the date in a more useful format. Like maybe a string that the JavaScript Date() method could take in its constructor. Should I be using one of these methods on the server side to convert it?

Answer 1

How do you insert the data and how do you retrieve it?

I use this, and it works fine:

use MongoDB\BSON\UTCDateTime;
$doc = [
    "input" => $input,
    "host" => gethostname(),
    "timestamp" => new UTCDateTime(NULL),
];
$ret = $logging->insertOne($doc); 

In order to convert a Mongo BSON date back to PHP Date, use MongoDB\BSON\UTCDateTime::toDateTime

If you need to work with JSON strings, then these commands would be useful:

use function MongoDB\BSON\toRelaxedExtendedJSON;
use function MongoDB\BSON\fromPHP;
use function MongoDB\BSON\toPHP;
use function MongoDB\BSON\fromJSON;

Here is an example how they could be used:

$match = []; 
$match["dp"] = 123; 

$find_time = []; 
$find_time["t0"] = ['$lte' => new UTCDateTime($value)];

$pipeline = []; 
array_push($pipeline, array('$match' => $find_time) ); 

$json = []; 
array_push($json, '{ "$unset": ["h", "sp", "tdp", "tdi"] }');
array_push($json, toRelaxedExtendedJSON(fromPHP(array('$match' => $match)))); 
foreach ($json as $stage) {
    array_push($pipeline, toPHP(fromJSON($stage)));
}

foreach ($collection->aggregate($pipeline, array('allowDiskUse' => true)) as $row) {
    array_push($ret, self::MongoToArray($row));
} 

Answer 2

I ended up coming up with this code that I tested and it solves the problem. It does feel like a bit of a 'hack' and I'm not sure why it's required, but it does work. It looks for fields of the structure:

anyField: {
   $date: {
       $numberLong: "1572318771000"
   }
}

and converts it into a UTCDateTime.

public static function fixMongoDBTimestampFields(&$record)
{
    foreach ($record as $fieldName => &$value)
    {
        if (is_array($value) || ($value instanceof Traversable))
        {
            if ( array_key_exists( '$date', $value) && is_array($value['$date']) && array_key_exists( '$numberLong', $value['$date']) )
            {
                $millisecs = $value['$date']['$numberLong'];
                $value = new MongoDB\BSON\UTCDateTime($millisecs);
            }

            self::fixMongoDBTimestampFields($value);
        }
    }
    unset($value);
}