Get looked up array count for a document - php

Question

i have 2 collections : words and phrases
Each word document has an array of phrases id's. And each phrase can be active or inactive.
For example :
words : {"word" => "hello", phrases => [1,2]}{"word" => "table", phrases => [2]}
phrases :{"id" => 1, "phrase" => "hello world!", "active" => 1}{"id" => 2, "phrase" => "hello, i have already bought new table", "active" => 0}
I need to get count of active phrases for each word.
In php i do it like this:
1. get all words
2. for each word get count of active phrases with condition ['active' => 1]
Question: How can i get words with active phrases count in one request? I tried to use MapReduce, but i need to make a request for each word to get count of active phrases.
UPD:
In my test collection there are 92 000 phrases and 23 000 words.
I have already tested both variant: with php loop for each word in which i get phrases count and aggreagation function in mongo.
But i changed aggregation pipeline in commets below because of phrases_data. It is array, so i can't use $match on it. I use $unwind after $lookup.
[ '$unwind' => '$5'],
[
'$lookup' => [
'from' => 'phrases_926ee3bc9fa72b029e028ec90e282072ea0721d1',
'localField' => '5',
'foreignField' => '0',
'as' => 'phrases_data'
]
],
[ '$unwind' => '$phrases_data'],
[ '$match' => [ 'phrases_data.3' => 77] ], //phrases_data.3 => 77 it is similar to phrases_data.active => 1
[ '$group' =>
[
'_id' => ['word' => '$1', 'id' => '$0'],
'active_count' => [ '$sum' => 1]
]
],
[ '$match' => [ 'active_count' => ['$gt' => 0]] ],
[ '$sort' =>
[
'active_count' => -1
]
]
The problem is that $group command take 80% of process time. And it is much slower than php loop. Here is my results for test collection:
1. Php loop (get words-> get phrases count for each word): 10 seconds
2. Aggregation function : 20 seconds

Answer 1

db.words.aggregate([
{ "$unwind" : "$phrases"},
{
"$lookup": {
"from": "phrases",
"localField": "phrases",
"foreignField": "id",
"as": "phrases_data"
}
},
{ "$match" : { "phrases_data.active" : 1} },
{ "$group" : {
"_id" : "$word",
"active_count" : { $sum : 1 }
}
}
]);
You can use above aggregation pipeline :
Unwind the phrases array from words collection documen as separate document
do a lookup(join) in phrases collection using unwinded phrases
filter the phrases and check for active using $match
Finally group phrases by word and count using $sum : 1