PHP MongoDB map reduce db assertion failure

问题

My first go at Map/Reduce using PHP/MongoDB. I am stuck with an error when running the MapReduce command.

My code:

$map = "function () {".                                                                                                             
"emit(this.topic_id, {re_date:this.date_posted}); " .                                                                     
"}";

$reduce = "function (key, values) {" . 
"var result = {last_post: 0};" .                                                                                                 
"var max = ISODate('1970-01-01T00:00:00Z');" .                                                                             
"values.forEach(function (value) {" .
       "if (max == ISODate('1970-01-01T00:00:00Z')) {" .
           "max = value.re_date;}" .
      "if (max < value.re_date) {max = value.re_date;}});" .    
"result.last_post = max;" .                                                                                   
"return result;"  .                                                                                              
"}";



$mapFunc = new MongoCode($map);
$reduceFunc = new MongoCode($reduce);

$collection = new MongoCollection($db, 'posts');
$command = array(
'mapreduce' => $collection,
'map' => $mapFunc,
'reduce' => $reduceFunc,
"query" => array("topic_id" => "2116"),
"out" => array("merge" => "eventCounts"));


$threadInfo = $db->command($command);

$threadsCollection = $db->selectCollection($threadInfo['result']);

$stats = $statsCollection->find();

foreach ($stats as $stat) {
    echo $stats['_id'] .' Visited ';
    foreach ($stats['value']['types'] as $type => $times) {
        echo "Type $type $times Times, ";
    }
    foreach ($stats['value']['tags'] as $tag => $times) {
        echo "Tag $tag $times Times, ";
    }
    echo "\n";
}

When I run the command I'm getting back the error:

assertion wrong type for field (mapreduce) 3 != 2 assertionCode 13111
errmsg db assertion failure
ok 0

I followed pretty closely the example here so I'm not sure what is going wrong. Any suggestions appreciated.

回答1:

It is important to remember when using mapReduce() that the return value of the reduce() function needs to be the same shape as the one that you expect to get in the 'values' element of reduce() function -- and that, in turn, needs to be the same shape as what is emitted by the emit() function.

Given a collection containing documents of the following form:

> db.posts.count();
1000
> db.posts.findOne();
{
    "_id" : 0,
    "date_posted" : ISODate("2012-04-04T05:54:44.535Z"),
    "topic_id" : "sierra"
}

The following code will produce the output you want:

<?php

$conn = new Mongo("localhost:$port");
$db = $conn->test;
$collection = $db->tst;

$map = new MongoCode(
    "function() { emit( this.topic_id, { last_post: this.date_posted } ); }"
);

$reduce = new MongoCode(
  "function(key, values) { ".
      "var max = ISODate('1970-01-01T00:00:00Z'); ".

      "values.forEach(function(val) { ".
          "if ( max < val.last_post ) max = val.last_post; ".
      "}); ".

      "return {last_post : max}; " .
  "}"
);


$result = $db->command( array(
    "mapreduce" => "posts",
    "map" => $map,
    "reduce" => $reduce,
    "query" => array( "topic_id" => "alpha"), 
    "out" => array( "merge" => "lastPosts")
    )
);
echo "result: "; print_r($result);

$collection = $db->lastPosts;
$cursor = $collection->find()->limit(6);

date_default_timezone_set("UTC");
foreach( $cursor as $doc ) {
    $date = date( "r", $doc['value']['last_post']->sec );
    echo $doc['_id'] . " last visited at " . $date ."\n" ;
}

?>

来源：https://stackoverflow.com/questions/11742986/php-mongodb-map-reduce-db-assertion-failure

标签

php

mongodb

MapReduce