MongoDB get document nested array by id

Question

I have a processes document with a nested attachments array, I want to return get the fileName with the processes _id and attachment _id.

I have tried many options, my latest attempt still return all items from the attachments array. I only want the attachment that matches the attachment id past in.

db.getCollection('processes').find(
{$and: [ { "_id" : ObjectId("5a9455d7854cd987a40b1ba4") }, 
{ "attachments._id" : ObjectId("5a983da6201ba5a2302fb38f") }]},
{'attachments._id': 1, 'attachments.fileName': 1}
)

Any suggestion is greatly appreciated, thanks!

mickl · Accepted Answer · 2018-03-02 19:02:30Z

3

You can use $elemMatch in projection to get only one filtered subdocument from nested array:

db.getCollection('processes').find(
    { "_id" : ObjectId("5a9455d7854cd987a40b1ba4") },
    { attachments: { $elemMatch: { _id: ObjectId("5a983da6201ba5a2302fb38f") } } } )

answered Mar 2, 2018 at 19:02

mickl

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1 Comment

user752746 Over a year ago

Many thanks Mickl!, That works exactly how I wanted to.

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