Populate nested array objects using aggregate in mongodb

Question

Im trying to populate the second nested array after using aggregate $lookup.

This is my original array.

 {
    "_id" : ObjectId("607da9c0c7cb26384c7810a6"), 
    "date" : ISODate("2021-04-20T00:00:00.000+0000"), 
    "clientID" : "601e6dc61766587af8ce76db", 
    "medications" : [
        {
            "_id" : ObjectId("6065de3aa95e721f587f7528")
        }, 
    ]
}

{
   from: "medications",
   localField: "medications._id",
   foreignField: "_id",
   as: "medications",
}

after using aggregate $lookup I get this result, but I still have nested array "inventory" that I need to populate. I tried adding another $lookup pipeline, but I don't know how the right way to do that.

{
    "_id" : ObjectId("607da9c0c7cb26384c7810a6"), 
    "date" : ISODate("2021-04-20T00:00:00.000+0000"), 
    "clientID" : "601e6dc61766587af8ce76db", 
    "medications" : {
        "_id" : ObjectId("6065de3aa95e721f587f7528"), 
        "medication": "med 1"
        "schedule": ["9am", "10pm"]
        "inventory":  "ObjectId("6076d55ab6aeb947dca85877")"
    }
}

This is the inventory item

{
   "_id" : ObjectId("6076d55ab6aeb947dca85877"), 
   "item": "Inventory item 1",
   "Qty": "10"
}

Expected Output

{
    "_id" : ObjectId("607da9c0c7cb26384c7810a6"), 
    "date" : ISODate("2021-04-20T00:00:00.000+0000"), 
    "clientID" : "601e6dc61766587af8ce76db", 
    "medications" : {
        "_id" : ObjectId("6065de3aa95e721f587f7528"), 
        "medication": "med 1"
        "schedule": ["9am", "10pm"]
        "inventory":  {
              "_id" : ObjectId("6076d55ab6aeb947dca85877"), 
              "item": "Inventory item 1",
              "Qty": "10"
         }
    }
}

CyberMessiah · Accepted Answer · 2021-04-30 07:04:30Z

1

You can try this one or alternatively use population.

{
   from: "medications",
   localField: "medications._id",
   foreignField: "_id",
   as: "medications",
}
, {
  $unwind: {
    path: "$medications",
    preserveNullAndEmptyArrays: true
  }
}, {
  $lookup: {
    from: "inventory",
    localField: "inventory._id",
    foreignField: "_id",
    as: "medications.inventory",
  }
}

You may check the $unwind in the official documentation. Just pay attention to the appropriate localField and foreignField.

answered Apr 30, 2021 at 7:04

CyberMessiah

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1 Comment

Mishhub Mohammed Over a year ago

Is there any other way to expand multiple nested references. Cz its weird to code 4 or 5 lookups just to expand nested references.

Sagar Darekar · Accepted Answer · 2022-06-06 03:56:21Z

0

use populate() to expand nested references.

schemaModel.populate(result, {path: 'result'});

See more at Mongoose docs

edited Jun 6, 2022 at 3:56

Sagar Darekar

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answered Jun 3, 2022 at 9:07

Prema Pandian

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