Searching for multiple values in a nested array

Question

I have the following collection:

{
 _id: 1,
 docs: [{
          name: file1,
          labels: [label1, label2, label3, label4]
        },{
          name: file2,
          labels: [label3, label4]
        },{
          name: file3,
          labels: [label1, label3, label4]
        }]
 }

When a user searches for labels, I need to get all the docs that have those labels.

So if a user searches for "label1" and "label3", I need to get "file1" and "file3". At the moment I have the following code:

    var collection = db.collection(req.user.username);

    collection.aggregate([
      // Unwind each array
      { "$unwind": "$docs" },
      { "$unwind": "$docs.labels" },

      // Filter just the matching elements
      {
          "$match": {
              "docs.labels": { "$all": ["label1", "label3"] }
          }
      }
    ]).toArray(function (err, items) {
        res.send(items);
    });

This works fine if I only search for "label1" or "label3", but not the two together. Can you please help me with this, since I haven't found an answer that works myself.

What is your mongod version?

Sede
– Sede

2017-01-02 20:00:50 +00:00
Commented Jan 2, 2017 at 20:00 — Sede
– Sede, Commented Jan 2, 2017 at 20:00
Why you didn't use mongoose module?

Heartbit
– Heartbit

2017-01-02 20:03:14 +00:00
Commented Jan 2, 2017 at 20:03 — Heartbit
– Heartbit, Commented Jan 2, 2017 at 20:03
@Styvane my mongo is version 3.2.10

Mathias
– Mathias

2017-01-02 20:04:05 +00:00
Commented Jan 2, 2017 at 20:04 — Mathias
– Mathias, Commented Jan 2, 2017 at 20:04

Sede · Accepted Answer · 2017-01-02 20:14:31Z

1

You can efficiently do this by $filtering your documents in the $project stage.

let inputLabels = ["label1", "label3"];

collection.aggregate([
    { "$match": { "docs.labels": { "$all": inputLabels }}}, 
    { "$project": { 
        "docs": { 
            "$filter": { 
                "input": "$docs", 
                "as": "doc", 
                "cond": { "$setIsSubset": [ inputLabels, "$$doc.labels" ] }
            }
        }
    }}
])]).toArray(function (err, items) {
        res.send(items);
    });

answered Jan 2, 2017 at 20:14

Sede

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1 Comment

Mathias Over a year ago

Thank you very much!! I tried using $project and $filter myself, but I wasn't able to get the desired result as I didn't fully understand it.

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