I have a document that I want to group by some specific fields, and for the remaining fields that are not included in the groupby, I want to include them in an embedded array.

An example, let's say that I have the following data

[
{"owner": "A", "pet": "dog", "pet_name": "wouf"},
{"owner": "A", "pet": "cat", "pet_name": "miaou"},
{"owner": "B", "pet": "dog", "pet_name": "wouf_wouf"},
]

I want to group this data by the field owner and the remaining fields pet and pet_name, I want to group them in an array named animals.

Expected result:

[
{
    "owner": "A",
    "animals": [
        {"pet": "dog", "pet_name": "wouf"},
        {"pet": "cat", "pet_name": "miaou"},
    ],
},
{ 
    "owner": "B",
    "animals": [{"pet": "dog", "pet_name": "wouf_wouf"}]
},
]

CodePudding user response：

Query

• group by $owner, and $push
• we dont have an operator to remove a field from a document(remove the owner), so a literal document is used, to keep only the pet/pet_name
• finally rename _id to owner and remove the _id

Playmongo

aggregate(
[{"$group": 
   {"_id": "$owner",
    "animals": {"$push": {"pet": "$pet", "pet_name": "$pet_name"}}}},
 {"$set": {"owner": "$_id", "_id": "$$REMOVE"}}])