Delete multiple occurences of same object

Question

In our collection, there's structure like:

Object: //below is object metadata from mongo
    _id
    created_at
    lang
    source
    object: //this is real object data from our db
        id
        created_at
        object_class

I ran below query on this collection:

db.getCollection('foo').aggregate(
    [
    {
        $match: {
            lang: 'bar', 
            pushed_at:{
            $gte: new ISODate("2015-11-09T00:00:00.000Z"),
            $lt: new ISODate("2015-11-10T00:00:00.000Z")
            }
        }
    },
    {
        $group: {
            _id: "$object.id",
            occurences: {$sum: 1}
        }
    },
    {
        $match: {
            occurences: {$gt: 1}
        }
    }
])

Which returned: Alt text

It appears that we got duplicate entries in our collection. By duplicate I mean objects with same Object.object.id. I'd like to remove redundant occurences using results from agreggate function I used. Notice that I don't want to delete anything, just rendundant ones, so above aggregate returns occurences: 1.

How to do this, also using results from aggregation?

Can you edit your question to include a Minimal, Complete, and Verifiable example, i.e. some sample data just enough to produce the desired result and the expected output from that sample data? — chridam
– chridam, Commented Nov 10, 2015 at 11:25

Mateo Barahona · Accepted Answer · 2015-11-12 06:39:18Z

1

I think you can try that in the shell :

db.foo.aggregate(
    [
    {
        $match: {
            lang: 'bar', 
            pushed_at:{
            $gte: new ISODate("2015-11-09T00:00:00.000Z"),
            $lt: new ISODate("2015-11-10T00:00:00.000Z")
            }
        }
    },
    {
        $group: {
            _id: "$object.id",
            occurences: {$sum: 1}
        }
    },
    {
        $match: {
            occurences: {$gt: 1}
        }
    }
]).result.forEach(function(x) {
    if(x.occurences > 1) {  
        for(i=0;i<x.occurences - 1;i++) {
            db.foo.remove({"object.id":x._id}, true);
        }
    }
}
);

edited Nov 12, 2015 at 6:39

answered Nov 11, 2015 at 19:54

Mateo Barahona

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7 Comments

ex3v Over a year ago

Thanks! That helps a lot!

ex3v Over a year ago

Sorry for side question but I wonder if, in general, it is possible to call methods like find() on previous query results?

Mateo Barahona Over a year ago

I'm not sure I understand, can you be more specfic ?

ex3v Over a year ago

Let's say that above aggregate produces results that I want to filter using another find() method, and in the end do something with them, like: db.col.aggregate(foo).find(using foo).count().

Mateo Barahona Over a year ago

But you can do à batch of if to match multiple conditions in your foreach

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