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Reputation: 9738

Selecting an Object in Array

I want to select an object within an array with id condition. In the below img i want to select [0].

enter image description here

db.users.find({"injury._id": ObjectId("537233061845d2ec10000071")})

Thankx for Help.

Upvotes: 1

Views: 49

Answers (1)

Neil Lunn
Neil Lunn

Reputation: 151112

I'm guessing here that you want to only see the selected array element in the document you are searching for. Use projection:

db.users.find(
    { "injury._id": ObjectId("537233061845d2ec10000071")},
    { "injury.$": 1 }
)

That just returns the matching element rather than all of them.

If you expect more than one match ( unlikely with an ObjectId, but for future reference ) then use the .aggregate() method instead:

db.users.aggregate([

    // Match documents first, helps reduce the pipeline
    { "$match": {
       "injury._id": ObjectId("537233061845d2ec10000071")
    }},

    // Unwind the array
    { "$unwind": "$injury" },

    // Actually match the elements
    { "$match": {
       "injury._id": ObjectId("537233061845d2ec10000071")
    }},

    // Group back if you really want arrays
    { "$group": {
        "_id": "$_id",
        "injury": { "$push": "$injury" },
        // and use "$first" for any other fields
    }}
])

So now you know what to do when you come up against that one as well.

Upvotes: 2

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