How to Project an Element in an Array of Objects in mongoDB for All Documents from a Collection-CodePudding

I have an array of objects in my company collection holding grouped values as follows:

"groups" : [
        {
            "id" : "d278c44333",
            "name" : "group 1"
        }
    ],

so in mongoDB it would be company > groups > 0 > id or name

I want to project all of the documents that have the groups array of objects and retrieve the name.

How can I do that?

Here is what i tried:

db.getCollection("Company").aggregate([
            
    {
        $match: { 
            "companyID": "323452343",

        }
    },

    {
        $project: { 
            //this only projects groupName with an array with 0 elements inside.
            groupName: "$groups.0.name"

         }
        
    }

])

EDIT:

expected result:

CodePudding user response：

For the specific case of the first item use:

db.collection.aggregate([
  {
    $project: {
      groupName: {
        $first: "$groups.name"
      }
    }
  }
])

See how it works on the playground example

For mongodb version older than 4.2 use:

db.collection.aggregate([
  {
    $project: {
      groupName: {
        $arrayElemAt: ["$groups.name", 0]
      }
    }
  }
])

CodePudding user response：

I finally found the right way to query and project the nested array of object as follows:

I had to use $arrayElemAt as such:

db.getCollection("Comapny").aggregate([
            
    {
        $match: { 
            "companyID": "123456789",
              
               
        }
    },
    
    {
        $sort: { _updated_at: -1 }
    },
        
    {
        $project: { 
            _id: "$_id",
           
            groups: {$arrayElemAt: [ "$groups.name", 0 ] },               

         }
        
    }

])