Mongo: querying for values nested in child arrays where keys are variable

Question

I'm trying to build a Mongo query where I can select documents based on the value inside a child array where the embedded array's keys will change from document to document.

In the following example, we have three document arrays. Pulling the name of each wine is trivial. The problem comes when I want to select the wines that have tasting results greater than 20. The problem is that I don't know the name of the flight when I run the query; it could be anything.

Therefore, I can't just check against the values of the embedded array.

I've thought about something like

$ary_query = array('tasting_results.*' => '$gt: 20');

but apparently wildcards don't work in Mongo (at least not like that). Any ideas?

Here's the example arrays:

ary_wines = array(
"name" => "Ripple",
"year" => "2013",
"style" => "cabernet", 
"size" => "750ml",
"tasting_results" => array (
    "flight_42" => 12,
    "flight_2" => 18,
    "flight_33" => 7 
    )
)

ary_wines = array(
"name" => "Riunite",
"year" => "2012",
"style" => "White Zinfandel", 
"size" => "1.5L",
"tasting_score" => array (
    "flight_6" => 14,
    "flight_54" => 21,
    "flight_98" => 3 
    )
)

ary_wines = array(
"name" => "Maneschewitz",
"year" => "2012",
"style" => "Grape Juice", 
"size" => "500ml",
"tasting_score" => array (
    "flight_7" => 12,
    "flight_41" => 26,
    "flight_9" => 3 
    )
)

user1207456 · Accepted Answer · 2012-03-28 01:08:09Z

2

Well, technically you can do a table scan style query with the $where clause:

db.wines.find({$where: function() {
    var keys = Object.keys(this.tasting_score);
    keys.forEach(function(key) {
        if(this.tasting_score[key] > 20) { return true; }
    });
    return false;
});

But, I implore you, this is a terrible idea, and it would be far better to put your data into the database in an indexable fashion where you can use standard query methods. Exactly how you should do so depends on the how your application is going to manipulate the data, but at the very least you can pre-process on insertion and have a maxTastingScore parameter in your object to query if this is the only query that doesn't fit your data structure.

answered Mar 28, 2012 at 1:08

user1207456

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2 Comments

DenverMatt Over a year ago

Thanks David, yeah, I was thinking about something like this, but then discarded it because it seems like it wouldn't scale well. So, I guess I need to change the way I'm building the documents, is basically what you're saying.

user1207456 Over a year ago

Yeah, MongoDB gives you a performance boost if you can find the right document structure. If there isn't one good structure, it may make more sense to go with PostgreSQL or in the opposite end with Neo4j. But after some thinking, perhaps you can do it with a structure like: tasting_score: [ { flight_num: 7, score: 20}, { flight_num: 18, score: 7 }, ...]. Then you can db.wines.find({"tasting_score.score": { $gt: 20 } }). It would depend on what other queries you intend to do, of course.

Community · Accepted Answer · 2017-05-23 10:08:40Z

0

Can you try filtering items individually and doing something like an OR?

I have a structure along the lines of

"entities": {
    "user_mentions": {
    "0": {
        "indices": {
            "0": 0,
            "1": 10 
        }
    },
    "1": {
        "indices": {
            "0": 41,
            "1": 51 
         }
    } 
}

The query can looks like so:

{
"entities.user_mentions.indices.0": {$gt:10},
"entities.user_mentions.indices.1": {$gt:20}
}

Also, refer MongoDB wildcard in the key of a query

edited May 23, 2017 at 10:08

CommunityBot

11 silver badge

answered Mar 28, 2012 at 1:34

Socratees Samipillai

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