How to select part of an array and filter in Mongo?

Question

I have a collection in Mongo that contains documents that look like this:

{
    name: "Bob",
    destinations:
    [
        {
            city: "Dallas",
            state: "Texas",
            isBusiness: "true",
        }, {
            city: "San Diego",
            state: "California",
            isBusiness: "true",
        }   
    ]
},
{
    name: "Sue",
    destinations:
    [
        {
            city: "Las Vegas",
            state: "Nevada",
            isBusiness: "false",
        }, {
            city: "Sacramento",
            state: "California",
            isBusiness: "true",
        }   
    ]
}

I want to query this collection so that I receive the name of each person along with the city of each destination within the state of California, but not the isBusiness value which should be ignored.

The result of the query should be:

[
    {
        name: "Bob",
        city: "San Diago",
    },
    {
        name: "Sue",
        city: "Sacramento"
    }
]

This example is a bit contrived, but how do I do this?

Alex Blex · Accepted Answer · 2018-03-13 15:32:23Z

1

Quite basic aggregation, not sure what to explain about it:

db.collection.aggregate([
    {$unwind: "$destinations"},
    {$match: {"destinations.state":"California"}},
    {$project: {_id:0, name: 1, city: "$destinations.city"}}
])

Docs:

answered Mar 13, 2018 at 15:32

Alex Blex

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Krishna · Accepted Answer · 2018-03-13 14:58:26Z

0

db.collectionName.find({"destinations.state":"California"},{name:1,"destinations.city":1})

answered Mar 13, 2018 at 14:58

Krishna

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2 Comments

Vivian River Over a year ago

This is not quite right. It does correctly extract the city from the destinations array, but it still returns all the cities, not just the ones in California.

Krishna Over a year ago

yep. the posted answer with aggregation is your solution.

Rubin Porwal · Accepted Answer · 2018-03-15 08:13:13Z

0

$elemMatch operator of MongoDB is used to apply filter over an array of elements.

According to description as mentioned into above question please try find executing following find operation into MongoDB shell.

db.collection.find({
    destinations: {
        $elemMatch: {
            state: "California"
        }
    }
}, {
    'destinations.$': 1,
    name: 1,
    _id: 0
})

answered Mar 15, 2018 at 8:13

Rubin Porwal

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