MongoDB $查找一个文档的对象数组

Question

我在网上搜索过，但找不到任何符合我的情况。情况如下。

我正在使用聚合将一个集合和一个来自另一个集合的文档组合在一起

restaurants.aggregate([
  {
    $match: {
      _id: {
        $in: idList
      }
    }
  },
  {
    $lookup: {
      from: "tags",
      localField: "details.restaurantType",
      foreignField: "details.restaurantType._id",
      as: "types"
    }
  },
  {
    $project: {
      restaurantName: "$details.restaurantName",
      restaurantType: "$details.restaurantType",
      type: {
        $filter: {
          input: "$types",
          as: "type",
          cond: {
            $eq: ["$$type._id", "$details.restaurantType"]
          }
        }
      },
      currency: "$details.currency",
      costPerPax: "$details.costPerPax"
    }
  }
]);

当前结果

我当前结果中的“类型”字段是 []，我需要一个匹配的值

[
    {
        "id": "5c20c7a0036dda80a8baabcc",
        "restaurantName": "Villagio Restaurant Sutera Mall",
        "type": [],
        "currency": "RM",
        "costPerPax": 22,
    },
    {
        "id": "5c20ceb07715216d3c217b7a",
        "restaurantName": "Thai Food Thai Now Sutera Mall",
        "type": [],
        "currency": "RM",
        "costPerPax": 16,
    }
]

预期结果

我需要“类型”字段与来自另一个集合的匹配标记名称，例如这样

[
    {
        "id": "5c20c7a0036dda80a8baabcc",
        "restaurantName": "Villagio Restaurant Sutera Mall",
        "type": "Western",
        "currency": "RM",
        "costPerPax": 22,
    },
    {
        "id": "5c20ceb07715216d3c217b7a",
        "restaurantName": "Thai Food Thai Now Sutera Mall",
        "type": "Thai",
        "currency": "RM",
        "costPerPax": 16,
    }
]

额外信息

餐厅收藏的两份文件

    {
        "details": {
            "restaurantName": "Villagio Restaurant Sutera Mall",
            "restaurantType": "5c01fb57497a896d50f498a8"
        },
        "_id": "5c20c7a0036dda80a8baabcc",
        "status": "OP",
        "__v": 0
    },
    {
        "details": {
            "restaurantName": "Kingshahi Japanese Shop",
            "restaurantType": "5c01fb57497a896d50f49879"
        },
        "_id": "5c20cb4fb7e75180480690c2",
        "status": "OP",
        "__v": 0
    } 

标签集合中的一个文档

        {
            "_id": "5c01fb57497a896d50f49876",
            "details": {
                "restaurantTypeId": "5c01fb57497a896d50f49877",
                "restaurantTypes": [
                    {
                        "_id": "5c01fb57497a896d50f49879",
                        "name": "Asian",
                        "counter": 1
                    },
                    {
                        "_id": "5c01fb57497a896d50f4987a",
                        "name": "Bakery",
                        "counter": 0
                    }
                ]
            }
        }

Answer 1

您可以使用以下优化的聚合管道

db.restaurants.aggregate([
  { "$lookup": {
    "from": "tags",
    "let": { "restaurantType": "$details.restaurantType" },
    "pipeline": [
      { "$match": {
        "$expr": { "$in": ["$$restaurantType", "$details.restaurantTypes._id"] }
      }},
      { "$unwind": "$details.restaurantTypes" },
      { "$match": {
        "$expr": { "$eq": ["$details.restaurantTypes._id", "$$restaurantType"] }
      }}
    ],
    "as": "types"
  }},
  { "$project": {
    "restaurantName": "$details.restaurantName",
    "restaurantType": "$details.restaurantType",
    "type": { "$arrayElemAt": ["$types.details.restaurantTypes.name", 0] },
    "currency": "$details.currency",
    "costPerPax": "$details.costPerPax"
  }}
])