How to make the "join" of an array of objects ids with MongoDB

Question

I'm facing some dificult to make this query with the MongoDB Aggregation Framrwork.

I have a order collection that has an array of objects ids from products example:

{
  _id: "5759b760aeacbfa420943d84",
  products: [
    "57718a2c9473f30ae88d1875",
    "57727d988d7e581809b454a1",
    "577bda7da756e2180507a944"
  ]
}

Here is an example of one document from my products ocllection:

{
  _id: "57718a2c9473f30ae88d1875",
  name: "Soap A"
}

How can I make an aggregation query in orders to get a list of contained products documents?

Tim · Accepted Answer · 2016-07-05 23:59:01Z

1

The short answer you can't. Aggregate works only on one collection.

However if you are using mongoose you can use query and '.populate' method

i.e

CollectionModel.find({}).populate('products').exec(function(err, items) {})

more details on populate http://mongoosejs.com/docs/populate.html

but that only applicable to nodejs application however language you are using have a look at some ORM frameworks for mongo

I hope that helps

answered Jul 5, 2016 at 23:59

Tim

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2 Comments

Leandro Curioso Over a year ago

But internally does Mongoose make another query to assemble that right?

Tim Over a year ago

@LeandroCurioso One way to get around this by either modifying Order model to include data that you need from product (de-normalize) and other one is to do lookups after aggregate is finished

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