无法使Map / Reduce与MongoDB一起使用

Question

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I've got this code:

// construct map and reduce functions
$map = new MongoCode("
    function() { ".
        "var key = {date: this.timestamp.getFullYear()+this.timestamp.getMonth()+this.timestamp.getDate()};".
        "emit(key, {count: 1});
    }"
);

$reduce = new MongoCode("
    function(k, vals) { ".
        "var sum = 0;".
        "for (var i in vals) {".
            "sum += vals[i];". 
        "}".
        "return sum;".
    "}"
);

$dates = $db->command(array(
    "mapreduce" => "items", 
    "map" => $map,
    "reduce" => $reduce,
    //"query" => array("type" => "sale"),
    "out" => array("merge" => "distinct_dates")
    )
);

But get this error when testing:

Array ( [assertion] => map invoke failed: JS Error: TypeError: this.timestamp.getFullYear is not a function nofile_b:0 [assertionCode] => 9014 [errmsg] => db assertion failure [ok] => 0 ) Cron run finished.

Each object in the collection has a timestamp, from which I want to extract a date (Ymd), and put each distinct date in a new collection.

Answer 1

In MongoDB you cannot store Date objects as is. I suppose, that your timestamp has int type. I hope, if you will define your map function such way everything will be ok:

$map = new MongoCode("
    function(){
         var date = new Date(this.timestamp * 1000) //JS Date need milliseconds 
         var key = date.getFullYear() + date.getMonth() + date.getDate();
         emit(key, {count: 1})
    }
")

Answer 2

The problem lies in that your "timestamp" field is not of the correct type. If you stored it as a pure string, something like:

"timestamp" : "Wed May 05 2010 15:37:58 GMT-0400 (EDT)"

You will get this error. Changing it to the following will cause your map to work as expected:

new Date("Wed May 05 2010 15:37:58 GMT-0400 (EDT)")

You'll know you're on the right track when you see it stored as an ISODate() object in Mongo's output.