How to rename the columnname in mongodb using node js

Hari Smith

I tried to map two collections its working fine but I have doubt in how to rename the column name using mongodb.

promotion collection

{ 
    "_id" : ObjectId("5cf7679a0b0bed2e7483b998"),   
    "group_name" : "Latest",   
    "products" : 
   [ObjectId("5cecc161e8c1e73478956333"),ObjectId("5cecc161e8c1e73478956334")]
}

product collection

{ 
    "_id" : ObjectId("5cecc161e8c1e73478956333"), 
    "product_name" : "bourbon"
},
{ 
    "_id" : ObjectId("5cecc161e8c1e73478956334"), 
    "product_name" : "bour"
}

mapping query

db.promotional.aggregate(
     [
        {
           $lookup: {
             from: "product",
             localField: "products",
             foreignField: "_id",
             as: "products"
                   }
        },  
        {
           $project :{products :{_id:0}}  
        }

     ]
)

I got output

{ 
    "_id" : ObjectId("5cf7679a0b0bed2e7483b998"),   
    "group_name" : "Latest",   
    "products" : 
     [
       {  
         "product_name" : "bourbon"
       },
       {  
       "product_name" : "bour"
       }
     ]
}

Expected output

{ 
    "_id" : ObjectId("5cf7679a0b0bed2e7483b998"),   
    "group_name" : "Latest",   
    "products" : 
     [
       {  
         "name" : "bourbon"
       },
       {  
       "name" : "bour"
       }
     ]
}

How to rename productname to name using mongodb

Ashh

You can $map over the products array and can change the fields name

db.promotional.aggregate([
  { "$lookup": {
    "from": "product",
    "localField": "products",
    "foreignField": "_id",
    "as": "products"
  }},
  { "$addFields": {
    "products": {
      "$map": {
        "input": "products",
        "as": "product",
        "in": {
          "name": "$$product.product_name"
        }
      }
    }
  }}
])

If you are using mongodb version 3.6 and above

db.promotional.aggregate([
  { "$lookup": {
    "from": "product",
    "let": { "products": "$products" },
    "pipeline": [
      { "$match": { "$expr": { "$in": [ "$_id", "$$products" ] } } },
      { "$project": { "name": "$product_name", "_id": 0 }}
    ],
    "as": "products"
  }}
])

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