select字段的值作为数组mongoose / mongodb聚合

我有一个mongo查询

db.memberships.aggregate([{ '$match': { unit: new ObjectId('566fbaa1e63225b10bacac44') } }, { '$lookup': { from: 'seasons', localField: 'season', foreignField: '_id', as: 'season' } }, { '$unwind': '$season' }, { '$project': { season: { 'name': '$season.name', 'id': '$season._id' } } }, { '$group': { _id: '$_id', 'season': { '$addToSet': '$season' } } }, ]); 

哪个结果

 [ { "_id": ObjectId("56a0e5a860d8a6e41eda2ea3"), "season": [{ "name": "Summer", "id": ObjectId("56a0d6c692c26b8c019a2758") }] }, { "_id": ObjectId("56a0e56d60d8a6e41eda2e9e"), "season": [{ "name": "Summer", "id": ObjectId("56a0d6c692c26b8c019a2758") }] }, { "_id": ObjectId("56a0e53860d8a6e41eda2e9a"), "season": [{ "name": "Summer", "id": ObjectId("56a0d6c692c26b8c019a2758") }] }, { "_id": ObjectId("56a0e4d660d8a6e41eda2e94"), "season": [{ "name": "Winter", "id": ObjectId("5680dc01ba1e41f5066526fa") }] } ] 

我需要以这种格式得到结果

 { _id: [ // ids here ], seasons: [{ id: '56a0d6c692c26b8c019a2758', 'name': 'Summer' }, { id: '5680dc01ba1e41f5066526fa', 'name': 'Winter' } ] } 

查询必须返回具有2个属性id和season的单个文档。 季节必须是一个独特的季节。 每个赛季都应该包含一个id和一个名字。 感谢帮助！

Answer 1

使用$group步骤重新组织stream水线，使_id值为null以便为所有input文档整体计算累积值，从而将id字段创build为所有唯一ID的数组：

 var pipeline = [ { '$match': { unit: new ObjectId('566fbaa1e63225b10bacac44') } }, { '$lookup': { from: 'seasons', localField: 'season', foreignField: '_id', as: 'season' } }, { '$unwind' : '$season' }, { '$project': { season: {'name': '$season.name', 'id' : '$season._id'} } }, { '$group': { "_id": null, "id": { "$addToSet": "$_id" }, 'season': { '$addToSet': '$season' } } } ]; db.memberships.aggregate(pipeline);