作为子文档获取一个集合的数据在另一个文档中mongoDb

Question

我正在使用猫鼬。我有一个meta收集这样

{ 
    "_id" : ObjectId("597568f5cf12434674"), 
    "data": "test data", 
    "createBy" : "testing", 
    "modifyBy" : "testing", 
    "modifyDate" : ISODate("2017-07-24T03:26:45.350Z"), 
    "createDate" : ISODate("2017-07-24T03:26:45.350Z"), 
} 

这_id是叫orders作为metaId

{ 
    "_id" : ObjectId("597818bf5332f91213411"), 
    "type" : "food order", 
    "isActive" : true, 
    "files" : [ 
     { 
      "metaId" : "597568f5cf12434674", 
      "_id" : ObjectId("597818sdfasdaf2222") 
     } 
    ] 
} 

，当我拿到订单的细节我需要加入两个集合，所以我的最终结果将是另一个集合像这样

{ 
    "_id" : ObjectId("597818bf5332f91213411"), 
    "type" : "food order", 
    "isActive" : true, 
    "files" : [ 
     { 
      "metaId" : "597568f5cf12434674", 
      "data": "test data", 
      "createBy" : "testing", 
      "modifyBy" : "testing", 
      "modifyDate" : ISODate("2017-07-24T03:26:45.350Z"), 
      "createDate" : ISODate("2017-07-24T03:26:45.350Z"), 
      "_id" : ObjectId("597818sdfasdaf2222") 
     } 
    ] 
} 

我写了这个查询但返回空，我知道这将是inc直接，因为我希望元数据在订单中。

const query = db.orders.aggregate([ 
     {'$match': {'_id': _id}}, 
     {'$lookup': { 
     'localField': 'files.metaId', 
     'from': 'meta', 
     'foreignField': '_id', 
     'as': 'metaInfo' 
     }}, 
     {'$unwind': '$metaInfo'}, 
     {'$project': { 
     'type': 1, 
     'isActive': 1, 
     'metaInfo.data': 1 
     }} 
    ]); 

有反正我可以做这个mongo，我对mongodb很新。请提前帮助，谢谢。

Answer 1

上$lookup汇聚运营商不会与一个数组的工作“从”边，所以你必须先解开它：

db.getCollection('orders').aggregate([ 
    // matches a single document in the orders collection 
    {'$match': {'_id': ObjectId("59784eb56149554af36a5666")}}, 

    // unwinds orders.files so that it is no longer an array 
    {'$unwind': '$files'}, 

    // performs the lookup on the meta collection and assigns the 'looked up' sub document to the attribute: "files" 
    {'$lookup': { 
    'localField': 'files.metaId', 
    'from': 'meta', 
    'foreignField': '_id', 
    'as': 'files' 
    }} 
]); 

上面的命令将返回以下文件：

{ 
    "_id" : ObjectId("59784eb56149554af36a5666"), 
    "type" : "food order", 
    "isActive" : true, 
    "files" : [ 
     { 
      "_id" : ObjectId("59784e706149554af36a5621"), 
      "data" : "test data", 
      "createBy" : "testing", 
      "modifyBy" : "testing", 
      "modifyDate" : ISODate("2017-07-24T03:26:45.350Z"), 
      "createDate" : ISODate("2017-07-24T03:26:45.350Z") 
     } 
    ] 
} 

注意：这会使用从meta集合中查找的内容文档来填充文件属性，因此您将丢失files.metaId，但由于连接是从orders.files.metaId到meta._id文件子文档中_id的值与orders.files.metaId相同。你可以看到这一点，如果你稍微修改一下命令：

db.getCollection('orders').aggregate([ 
    // matches a single document in the orders collection 
    {'$match': {'_id': ObjectId("59784eb56149554af36a5666")}}, 

    // unwinds orders.files so that it is no longer an array 
    {'$unwind': '$files'}, 

    // performs the lookup on the meta collection and assigns the 'looked up' sub document to the attribute: "files" 
    {'$lookup': { 
     'localField': 'files.metaId', 
     'from': 'meta', 
     'foreignField': '_id', 
     'as': 'metaData' 
    }} 
    ]); 

这将返回：

{ 
    "_id" : ObjectId("59784eb56149554af36a5666"), 
    "type" : "food order", 
    "isActive" : true, 
    "files" : { 
     "metaId" : ObjectId("59784e706149554af36a5621") 
    }, 
    "metaData" : [ 
     { 
      "_id" : ObjectId("59784e706149554af36a5621"), 
      "data" : "test data", 
      "createBy" : "testing", 
      "modifyBy" : "testing", 
      "modifyDate" : ISODate("2017-07-24T03:26:45.350Z"), 
      "createDate" : ISODate("2017-07-24T03:26:45.350Z") 
     } 
    ] 
} 

在这files.metaId == metaData._id。