GardenModel表

{ display: true,
  itemList:
   [ { type: 1, count: 100 },
	 { type: 2, count: 99 },
	 { type: 3, count: 50 } ],
  _id: 5b2e0da2efa97927b06927ec,
  __v: 0 }

UserModel表

{ _id: 5b2e0da2efa97927b06927ed,
  nick: 'hehe',
  gender: 1,
  lastLogin: 2018-06-23T09:06:42.745Z,
  garden: 5b2e0da2efa97927b06927ec,
  __v: 0 }

查询如下：

async function test2(){
	let docs = await UserModel.aggregate([
		{
			$lookup:{
				from:"GardenModel",
				localField:"garden",
				foreignField:"_id",
				as:"gardenInfo"
			}
		}
	]);
	console.log(docs[0]);
}

但是输出如下：不知道为啥gardenInfo是空的

{ _id: 5b2e0da2efa97927b06927ed,
  nick: 'hehe',
  gender: 1,
  lastLogin: 2018-06-23T09:06:42.745Z,
  garden: 5b2e0da2efa97927b06927ec,
  __v: 0,
  gardenInfo: [] }

当我用robo进行相同操作时如下

db.getCollection('usermodels').aggregate([
{
	$lookup:{
				from:"gardenmodels",
				localField:"garden",
				foreignField:"_id",
				as:"gardenInfo"
		}
	}
])

{ “_id” : ObjectId(“5b2e52154c73cb22fc77b92c”), “nick” : “test”, “gender” : 1, “lastLogin” : ISODate(“2018-06-23T13:58:45.028Z”), “garden” : ObjectId(“5b2e52144c73cb22fc77b92b”), “__v” : 0, “gardenInfo” : [ { “_id” : ObjectId(“5b2e52144c73cb22fc77b92b”), “display” : true, “itemList” : [ { “type” : 1, “count” : 200 }, { “type” : 2, “count” : 99 }, { “type” : 3, “count” : 90 } ], “__v” : 0 } ] }