MongoDB multiple subqueries

Question

I'm kinda new to no-sql databases, so I have a question on subqueries here.

Let's imagine the following structure:

Type (_id, offerId)
Offer (_id, typeId, productId)
Product (_id, subId)

I need to find all types by subId.

I have no idea on how does it work for MongoDB, in SQL I'd do something like:

select * from Type where offerId in 
  (select _id from Offer where productId in
    (select _id from Product where subId = 'test'));

For MongoDB I tried to create some kind of aggregation query, but it doesn't work:

{
  "aggregate": "Type",
  "pipeline": [
    {
      "$lookup": {
        "from": "Offer",
        "localField": "_id",
        "foreignField": "typeId",
        "as": "subOffer"
      }
    },
    {
      "$lookup": {
        "from": "Product",
        "localField": "_id",
        "foreignField": "subOffer.productId",
        "as": "subProduct"
      }
    },
    {
      "$match": {
        "subProduct.subId": "test"
      }
    },
    {
      "$unwind": "$subProduct"
    },
    {
      "$unwind": "$subOffer"
    }
  ]
}

Any suggestions here?

score 1 · Accepted Answer · answered Aug 26 '20 at 16:31

You can try,

$lookup on offer collection using pipeline
$match type id
$lookup on product collection using pipeline
$match fields subId and productId
$match product is not [] empty
$match offer is not [] empty
$project remove offer field

db.type.aggregate([
  {
    $lookup: {
      from: "offer",
      let: { tid: "$_id" },
      as: "offer",
      pipeline: [
        { $match: { $expr: { $eq: ["$$tid", "$typeId"] } } },
        {
          $lookup: {
            from: "product",
            as: "product",
            let: { pid: "$productId" },
            pipeline: [
              {
                $match: {
                  $and: [
                    { subId: "test" },
                    { $expr: { $eq: ["$_id", "$$pid"] } }
                  ]
                }
              }
            ]
          }
        },
        { $match: { product: { $ne: [] } } }
      ]
    }
  },
  { $match: { offer: { $ne: [] } } },
  { $project: { offer: 0 } }
])

Playground

MongoDB multiple subqueries

1 Answers1