PHP MongoDB映射减少数据库断言失败

Question

我第一次使用PHP/MongoDB访问Map/Reduce。我在运行MapReduce命令时遇到了一个错误。

我的代码：

$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";
}

当我运行命令时，我会返回错误：

字段（mapreduce）3的断言类型错误！=2.分摊代码13111
errmsg数据库断言失败
ok 0

我非常仔细地遵循了这里的例子，所以我不确定出了什么问题。欢迎提出任何建议。

Answer 1

使用mapReduce（）时，需要记住的是，reduce（）函数的返回值需要与您期望在reduce函数的'values'元素中获得的形状相同，而这反过来又需要与emit（）函数发出的形状相同。

给定包含以下格式文件的集合：

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

以下代码将产生您想要的输出：

<?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" ;
}
?>