Mongodb 通过忽略数组中的重复项来计数文档

每次预约都有一些服务。我要查找每个服务的预约总数

我的文档如下所示：

[{
  "appointmentTag":"xyz",
  "services" : [
    {
      "name" : "service1",
      "estimatedTime":20
    },
    {
      "name" : "service2",
      "estimatedTime":40
    }
  ]
},
{
  "appointmentTag":"abc",
  "services" : [
    {
      "name" : "service2",
      "estimatedTime":100
    },
    {
      "name" : "service2",
      "estimatedTime":30
    }
  ]
}

   db.test.aggregate([
  {
    "$unwind": "$services"
  },
  {
    "$group": {
      "_id": "$services.name",
      "appointments": {
        "$addToSet": "$appointmentTag"
      }
    }
  },
  {
    "$project": {
      "ServiceName": "$_id","_id":0,
      "countOfAppointments": {
        "$size": "$appointments"
      }
    }
  }
])

预期产出如下：

{"serviceName":"service1", "count":1}
{"serviceName":"service2", "count":2}

我尝试的查询：

db.appointments.aggregate([
    {"$unwind": "$services"},
    {"$group": {
        "_id": "$services.name",
        "count": {"$sum":1}
    }}
]);

获得以下结果：

{"serviceName":"service1", "count":1}
{"serviceName":"service2", "count":3}

---

你做得几乎正确。展开后，当您按serviceName分组而不是计数时，请使用$addToSet of appointmentTag，然后计数该数组。大概是这样的：

[{
  "appointmentTag":"xyz",
  "services" : [
    {
      "name" : "service1",
      "estimatedTime":20
    },
    {
      "name" : "service2",
      "estimatedTime":40
    }
  ]
},
{
  "appointmentTag":"abc",
  "services" : [
    {
      "name" : "service2",
      "estimatedTime":100
    },
    {
      "name" : "service2",
      "estimatedTime":30
    }
  ]
}

   db.test.aggregate([
  {
    "$unwind": "$services"
  },
  {
    "$group": {
      "_id": "$services.name",
      "appointments": {
        "$addToSet": "$appointmentTag"
      }
    }
  },
  {
    "$project": {
      "ServiceName": "$_id","_id":0,
      "countOfAppointments": {
        "$size": "$appointments"
      }
    }
  }
])

---

你做得几乎正确。展开后，当您按serviceName分组而不是计数时，请使用$addToSet of appointmentTag，然后计数该数组。大概是这样的：

[{
  "appointmentTag":"xyz",
  "services" : [
    {
      "name" : "service1",
      "estimatedTime":20
    },
    {
      "name" : "service2",
      "estimatedTime":40
    }
  ]
},
{
  "appointmentTag":"abc",
  "services" : [
    {
      "name" : "service2",
      "estimatedTime":100
    },
    {
      "name" : "service2",
      "estimatedTime":30
    }
  ]
}

   db.test.aggregate([
  {
    "$unwind": "$services"
  },
  {
    "$group": {
      "_id": "$services.name",
      "appointments": {
        "$addToSet": "$appointmentTag"
      }
    }
  },
  {
    "$project": {
      "ServiceName": "$_id","_id":0,
      "countOfAppointments": {
        "$size": "$appointments"
      }
    }
  }
])