SQL 'UNION ALL' like implementation in MongoDB

Question

There are two collections:

Sales

{
  \"_id\" : ObjectId(\"5ba0bfb8d1acdc0de716e839\"),
  \"invoiceNumber\" : 1,
  \"saleDate\" : ISODate(\"2018-09-01T00:         


        

Answer 1

You can try below aggregation

db.sales.aggregate([
  { "$limit": 1 },
  { "$facet": {
    "collection1": [
      { "$limit": 1 },
      { "$lookup": {
        "from": "sales",
        "pipeline": [
          { "$match": {
            "date": { "$gte": ISODate("2018-09-01"), "$lte": ISODate("2018-09-10") },
            "customer.name": customerName
          }},
          { "$project": {
            "_id":0, "dated": "$saleDate", "heading": "Sale", "particulars": "$invoiceNumber",
            "amount": "$totalAmount", "modeOfPayment": null
          }}
        ],
        "as": "collection1"
      }}
    ],
    "collection2": [
      { "$limit": 1 },
      { "$lookup": {
        "from": "transactions",
        "pipeline": [
          { "$match": {
            "transactionDate": { "$gte": ISODate("2018-09-01"), "$lte": ISODate("2018-09-10") },
            "userId": userId, "partyName": customerName
          }},
          { "$project": {
            "_id":0, "dated": "$transactionDate", "heading": "Payment","particulars": "$transactionNumber",
            "amount": "$amount", "paymentMode": "$transactionMode"
          }}
        ],
        "as": "collection2"
      }}
    ]
  }},
  { "$project": {
    "data": {
      "$concatArrays": [
        { "$arrayElemAt": ["$collection1.collection1", 0] },
        { "$arrayElemAt": ["$collection2.collection2", 0] },
      ]
    }
  }},
  { "$unwind": "$data" },
  { "$replaceRoot": { "newRoot": "$data" } },
  { "$sort": { "dated": -1 }}
])