mongodb aggregation query for field value length's sum

Question

Say, I have following documents:

{name: 'A', fav_fruits: ['apple', 'mango', 'orange'], 'type':'test'}
{name: 'B', fav_fruits: ['apple', 'orange'], 'type':'test'}
{name: 'C', fav_fruits: ['cherry'], 'type':'test'}

I am trying to query to find the total count of fav_fruits field on overall documents returned by :

cursor = db.collection.find({'type': 'test'})

I am expecting output like:

cursor.count() = 3 // Getting

Without much idea of aggregate, can mongodb aggregation framework help me achieve this in any way:

1. sum up the lengths of all 'fav_fruits' field: 6

and/or

2. unique 'fav_fruit' field values = ['apple', 'mango', 'orange', 'cherry']

Sede · Accepted Answer · 2016-04-04 12:02:12Z

1

You need to $project your document after the $match stage and use the $size operator which return the number of items in each array. Then in the $group stage you use the $sum accumulator operator to return the total count.

db.collection.aggregate([
    { "$match": { "type": "test" } },
    { "$project": { "count": { "$size": "$fav_fruits" } } }, 
    { "$group": { "_id": null, "total": { "$sum": "$count" } } }
])

Which returns:

{ "_id" : null, "total" : 6 }

To get unique fav_fruits simply use .distinct()

> db.collection.distinct("fav_fruits", { "type": "test" } )
[ "apple", "mango", "orange", "cherry" ]

edited Apr 4, 2016 at 12:02

answered Apr 4, 2016 at 11:52

Sede

61.5k20 gold badges158 silver badges162 bronze badges

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

Comments

SiddAjmera · Accepted Answer · 2016-04-04 11:16:02Z

0

Do this to get just the number of fruits in the fav_fruits array:

db.fruits.aggregate([
    { $match: { type: 'test' } },
    { $unwind: "$fav_fruits" },
    { $group: { _id: "$type", count: { $sum: 1 } } }
]);

This will return the total number of fruits.

But if you want to get the array of unique fav_fruits along with the total number of elements in the fav_fruits field of each document, do this:

db.fruits.aggregate([
    { $match: { type: 'test' } },
    { $unwind: "$fav_fruits" },
    { $group: { _id: "$type", count: { $sum: 1 }, fav_fruits: { $addToSet: "$fav_fruits" } } }
])

edited Apr 4, 2016 at 11:16

answered Apr 4, 2016 at 11:06

SiddAjmera

39.6k7 gold badges78 silver badges114 bronze badges

Comments

Priyank_Vadi · Accepted Answer · 2016-04-04 11:09:38Z

0

You can try this. It may helpful to you.

db.collection.aggregate([{ $match : { type: "test" } }, {$group : { _id : null, count:{$sum:1} } }])

answered Apr 4, 2016 at 11:09

Priyank_Vadi

1,14811 silver badges27 bronze badges

Collectives™ on Stack Overflow

mongodb aggregation query for field value length's sum

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related