Arrays 常用模式字段，其模式位于数组中（Moongose）

我需要获取引用city_id的数据，city_id是一个模式，它链接到另一个模式的数组

},

现在，这是城市模式。我有一个位置模式，其中包含一个国家/地区关系：

import Country from './countrySchema';
const locationSchema = new Schema({
    region: {
       type: String,
       required: true,
       unique: true,
       dropDups: true
    },
    locations: [Country.schema]
},{ timestamps: true});

const locationModel = model("Location", locationSchema);

import City from './CitySchema';
const countrySchema = new Schema({
    country_name: {
        type: String,
        required: true,
        unique: true,
        dropDups: true
    },
    cities: [City.schema]
},{ _id: true, timestamps: true });

const countryModel = model("Country", countrySchema);

这是国家/地区架构，其中包含城市关系：

import Country from './countrySchema';
const locationSchema = new Schema({
    region: {
       type: String,
       required: true,
       unique: true,
       dropDups: true
    },
    locations: [Country.schema]
},{ timestamps: true});

const locationModel = model("Location", locationSchema);

import City from './CitySchema';
const countrySchema = new Schema({
    country_name: {
        type: String,
        required: true,
        unique: true,
        dropDups: true
    },
    cities: [City.schema]
},{ _id: true, timestamps: true });

const countryModel = model("Country", countrySchema);

这是城市模式：

const citySchema = new Schema({
    city_name: {
        type: String,
        required: true,
        unique: true,
        dropDups: true
    }
},{ _id: true, timestamps: true });

const cityModel = model("City", citySchema);

最后，这看起来像：

"_id": "5fa147b607f466ac1d536bce",
  "locations": [
    {
      "_id": "5fa147b607f466ac1d536bcf",
      "country_name": "Colombia",
      "cities": [
        {
          "_id": "5fa147b607f466ac1d536bd0",
          "city_name": "Medellín",
          "createdAt": "2020-11-03T12:06:14.914Z",
          "updatedAt": "2020-11-03T12:06:14.914Z"
        },
        {
          "_id": "5fa147b607f466ac1d536bd1",
          "city_name": "Bogotá",
          "createdAt": "2020-11-03T12:06:14.914Z",
          "updatedAt": "2020-11-03T12:06:14.914Z"
        }
      ],
      "createdAt": "2020-11-03T12:06:14.914Z",
      "updatedAt": "2020-11-03T12:06:14.914Z"
    },

如何获取城市信息？？非常感谢。

试试这个：

 locationModel.findOne({_id:"5fa147b607f466ac1d536bce"})
      .populate({ path:"locations",{path:"cities"}})
      .exec((err,location) => {
               if(err) reject(err);
               return resolve(location);   
            })`