Question

这是'公司'收集数据

{
  _id: "1",
  company: "ABC",
  addresses: [
    {
      _id: "2",
      address: "a1",
      district: "d1",
      city: "c1"
    },
    {
      _id: "3",
      address: "a2",
      district: "d2",
      city: "c2"
    },
    {
      _id: "4",
      address: "a3",
      district: "d3",
      city: "c3"
    }
  ]
}

这是'产品'集合数据

{
  product: "xyz",
  companyid: "1",           //_id of record in company's collection
  addresses: ["2", "4"]    //addresses _id of record in company's collection
},
{
  product: "pqr",
  companyid: "1",
  addresses: ["3", "4"]
}

现在我需要获得所有公司产品及其地址，如下所示

{
  product: "xyz",
  company: "ABC",
  addresses: [
    {
      _id: "2",
      address: "a1",
      district: "d1",
      city: "c1"
    },
    {
      _id: "4",
      address: "a3",
      district: "d3",
      city: "c3"
    }
  ]
},
{
  product: "pqr",
  companyid: "ABC",
  addresses: [
    {
      _id: "3",
      address: "a2",
      district: "d2",
      city: "c2"
    },
    {
      _id: "4",
      address: "a3",
      district: "d3",
      city: "c3"
    }
  ]
}

如果有数组，只有在产品中我们可以展开它们并执行查找。但是在这种情况下，两个集合中都有数组，那么我们如何比较它们或使用$ lookup来获得预期的输出呢？如果还有其他选择，请告诉我。

Answer 1

您可以尝试运行以下聚合操作以获得所需的结果：

db.product.aggregate([
    {
        "$lookup": {
            "from": "company",
            "localField": "companyid",
            "foreignField": "_id",
            "as": "company"
        }
    },
    { 
        "$addFields": {
            "company":  { "$arrayElemAt": ["$company", 0] }
        }
    },
    { 
        "$addFields": {            
            "addresses":  { 
                "$filter": {
                    "input": "$company.addresses",
                    "as": "ad",
                    "cond": {
                        "$setIsSubset": [
                            ["$$ad._id"],
                            "$addresses"
                        ]
                    }
                }
            }
        }
    },
    { "$project": { "company": 0 } }
])

如何在两个不同的集合中对数组使用$ lookup？

1 个答案: