Mongo Only Return Elements of Array Matching Query [duplicate]

Question

Given the following JSON example:

{
    _id: "55ef729a66d78d24008xxxx",
    name: "The right one"
    items: [{
        _id: "55ef729a66d78d24008xxxx",
        return: true
    }, {
        _id: "55ef729a66d78d24008xxxx",
        return: true
    }, {
        _id: "55ef729a66d78d24008xxxx",
        return: false
    }]
}

I want to write a query that specifies items.return = true and it should return:

{
    _id: "55ef729a66d78d24008xxxx",
    name: "The right one"
    items: [// 2 element array]
}

I've seen a lot of people suggest using $elemMatch, such as this question, but as it says, this

only return the first match

but this just returns the parent documents that have some value in the array matching items.return. So in the above example it would return all 3 array elements.

I want to completely ignore these array values in my return. I don't want to do it in the client, because I do a project using the items _id and don't want to waste the project if I don't need it.

Different question, that question refers to returning parent documents with the exact arrays that match, I need to alter the array itself. — KJ3
– KJ3, Commented Oct 26, 2015 at 19:08
It's not about the question but the answers provided to the question. There are several answers there that use the aggregation framework to return just the matched "elements" as that is the only tool ( aside from map reduce ) that is able to do so. — Blakes Seven
– Blakes Seven, Commented Oct 26, 2015 at 20:32

Alok Deshwal · Accepted Answer · 2015-10-26 21:05:26Z

3

Alternative not exact you want

db.items.aggregate(
      {$unwind:"$items"},
      {$match:{"items.return":true}}
)

answered Oct 26, 2015 at 21:05

Alok Deshwal

1,1369 silver badges20 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

jano · Accepted Answer · 2018-12-19 14:59:29Z

2

One alternative is to use $elemMatch. Check the docs, worth to notice is that it only returns first match!

db.items.find({}, {items: {$elemMatch: {return: "admin"}}}});

edited Dec 19, 2018 at 14:59

jano

7657 silver badges20 bronze badges

answered May 15, 2017 at 10:16

mirwaleed

777 bronze badges

1 Comment

RBT Over a year ago

From review queue: May I request you to please add some context around your source-code. Code-only answers are difficult to understand. It will help the asker and future readers both if you can add more information in your post.

Frol · Accepted Answer · 2015-10-27 14:03:09Z

1

You can use the aggregation framework, it is not the best solution though

db.collection.aggregate([
      {$unwind:'$items'},
      {$match:{'items.return':true}},
      {$group:{_id:'$_id', name: '$name',items:{$push:'$items'}}}
])

edited Oct 27, 2015 at 14:03

answered Oct 26, 2015 at 21:22

Frol

343 bronze badges

Collectives™ on Stack Overflow

Mongo Only Return Elements of Array Matching Query [duplicate]

3 Answers 3

Comments

1 Comment

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Linked

Related