Returning whole object in MongoDB aggregation

Question

I have Item schema in which I have item details with respective restaurant. I have to find all items of particular restaurant and group by them with 'type' and 'category' (type and category are fields in Item schema), I am able to group items as I want but I wont be able to get complete item object. My query:

db.items.aggregate([{
    '$match': {
        'restaurant': ObjectId("551111450712235c81620a57")
    }
}, {
    '$group': {
        id: {
            '$push': '$_id'
        }
        , _id: {
            type: '$type'
            , category: '$category'
        }
    }
}, {
    $project: {
        id: '$id'
    }
}])

I have seen one method by adding each field value to group then project it. As I have many fields in my Item schema I don't feel this will good solution for me, Can I get complete object instead of Ids only.

Answer 1

Well you can always use $$ROOT providing that your server is MongoDB 2.6 or greater:

db.items.aggregate([
    { '$match': {'restaurant': ObjectId("551111450712235c81620a57")}},
    { '$group':{
        _id : {
            type : '$type',
            category : '$category'
       },
       id: { '$push': '$$ROOT' },
    }}
])

Which is going to place every whole object into the members of the array.

You need to be careful when doing this as with larger results you are certain to break BSON limits.

I would suggest that you are trying to contruct some kind of "search results", with "facet counts" or similar. For that you are better off running a separate query for the "aggregation" part and one for the actual document results.

That is a much safer and flexible approach than trying to group everything together.