Question

I have a collection called contract and I would like to group using "a_id"

{
 a_id: 1,
 "name": "n1"
}
{
 a_id: 2,
 "name": "n2"
}
{
 a_id: 1,
 "name": "n3"
}
{
 a_id: 1,
 "name": "n4"
}
{
 a_id: 2,
 "name": "n5"
}

I want to group by "a_id" to show me the list of names associated.

{
 a_id: 1,
 values: ["n1", "n3", "n4"]
}
{
 a_id: 2,
 values: ["n2", "n5"]
}

My code:

db.contract.group({ 
      key:{a_id: 1}, 
      initial: {v: ''}, 
      reduce: function(doc, obj){ 
            v = v + " " + obj.name
      } 
}); 

My Output:

{
        "a_id" : 1,
        "v" : ""
    },
    {
        "asset_id" : 2,
        "v" : ""
    }

This doesn’t return the list of values, but mongd logs shows me list of names, How can I correct this?

Fixed

db.contract.group({
   key:{a_id: 1}, 
   initial: {v: []}, 
   reduce: function(obj, prev){ 
      prev.v.push(obj.name)
   }
});

Answer 1

Fixed

db.contract.group({
   key:{a_id: 1}, 
   initial: {v: []}, 
   reduce: function(obj, prev){ 
      prev.v.push(obj.name)
   }
});