按对象数组对文档进行分组

Question

文档示例

{
  _id: 1,
  entity: 'Transaction',
  approvals: [
    {
      userId: 1, // ObjectID
      final: true,
      approved: false,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 1,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
},
{
  _id: 2,
  entity: 'Transaction',
  approvals: [
    {
      userId: 1,
      final: true,
      approved: false,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 1,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
},
{
  _id: 3,
  entity: 'Transaction',
  approvals: [
    {
      userId: 1,
      final: true,
      approved: true,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 2,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
},
{
  _id: 4,
  entity: 'Transaction',
  approvals: [
    {
      userId: 1,
      final: true,
      approved: true,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 2,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
}

我想按照以下标准对此类文档进行分组：

• 实体
• approvals.approved
• approvals.userId
• approvals.final
• approvals.date

approvals 数组可以包含多个值，可能未排序，因为我需要按日期对它们进行排序；如果批准数量不同 - 两个对象属于不同的组。 这可能与使用 Mongodb 4.2 设施有关吗？最有效的方法是什么？我在考虑生成哈希，但不确定 MongoDB 是否有这样的功能。

想要的结果：

{
  ids: [1, 2],
  entity: 'Transaction',
  approvals: [
    {
      userId: 1,
      final: true,
      approved: false,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 1,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
}
{
  ids: [3, 4],
  entity: 'Transaction',
  approvals: [
    {
      userId: 1,
      final: true,
      approved: true,
      date: ISODate('2021-01-01'),
    },
    {
      userId: 2,
      final: true,
      approved: false,
      date: ISODate('2021-02-01'),
    }
  ]
}

Answer 1

可能是这样的：

 mongos> db.h.aggregate([      { $unwind:"$approvals"}   , {$group:{ _id:{ ent:"$entity" , app:"$approvals.approved" , fin:"$approvals.final" ,dat:"$approvals.date"  } ,count:{$sum:1}    }} , {$sort:{dat:1}}  ])
 { "_id" : { "ent" : "Transaction", "app" : true, "fin" : true, "dat" : ISODate("2021-02-01T19:35:37.883Z") }, "count" : 1 }
 { "_id" : { "ent" : "Transaction", "app" : true, "fin" : true, "dat" : ISODate("2021-02-01T19:41:37.931Z") }, "count" : 1 }