MongoDB：如何在一个文档中对嵌套数组进行分组？

Question

I have the following Collection:

{
    id: 23423-dsfsdf-32423,
    name: Proj1,
    services: [
         {
            id:sdfs-24423-sdf,
            name:P1_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-24jhh-sdf,
            name:P1_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-2jnbn3-sdf,
            name:P1_Service3,
            products:[{},{},{}]
         }
    ]
},
{
    id: 23423-cxcvx-32423,
    name: Proj2,
    services: [
         {
            id:sdfs-xvxcv-sdf,
            name:P2_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-xvwqw-sdf,
            name:P2_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-erdfd-sdf,
            name:P2_Service3,
            products:[{},{},{}]
         }
    ]
}

I need to return a document with an Array of all services:

{
    services: [
         {
            id:sdfs-24423-sdf,
            name:P1_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-24jhh-sdf,
            name:P1_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-2jnbn3-sdf,
            name:P1_Service3,
            products:[{},{},{}]
         },
         {
            id:sdfs-xvxcv-sdf,
            name:P2_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-xvwqw-sdf,
            name:P2_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-erdfd-sdf,
            name:P2_Service3,
            products:[{},{},{}]
         }
     ]
}

The most i got was :

db.projects.aggregate({"$group":{"_id":"services","services":{"$push":"$services"}}})

But this returns a document with an array of arrays and i want an array of objects:

{
    _id:"services",
    services:[
        [
            {
            id:sdfs-24423-sdf,
            name:P1_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-24jhh-sdf,
            name:P1_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-2jnbn3-sdf,
            name:P1_Service3,
            products:[{},{},{}]
         }
        ],
        [
            {
            id:sdfs-xvxcv-sdf,
            name:P2_Service1,
            products:[{},{},{}]
         },
         {
            id:sdfs-xvwqw-sdf,
            name:P2_Service2,
            products:[{},{},{}]
         },
         {
            id:sdfs-erdfd-sdf,
            name:P2_Service3,
            products:[{},{},{}]
         }
        ]
    ]
}

I can't figure out the arrays aggregation or join or union or whatever. Eventually i will have to do the same for the products also (getting all the products of all services of all projects as one array of products and return a document to the server but first thing first...

10x

Answer 1

You need to group on null _id so that all services get grouped in single document. Also $unwind the services array before grouping, else group will give you array of arrays

db.project.aggregate(
  {$unwind: '$services'},
  {$group: {_id:null, services: {$push: '$services'}}}
)