分层数据并使用 LINQ 合并两个数据集

问：

我正在尝试合并来自两个不同服务调用的数据。数据在结构上与此类似：

API 层中的 DTO：

public static class GetData
{
    public record Country
    {
        public Guid Id { get; set; }
        public List<State> States { get; set; }
    }

    public record State
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
        public List<City> Cities { get; set; }
    }

    public record City
    {
        // this Id is stored in Service B's DB as ItemId
        public Guid Id { get; set; }
        public string Name { get; set; }
        public Location Location { get; set; }
    }

    // From service B
    public record Location
    {
        public Guid Id { get; set; }
        public Guid ItemId { get; set; }
        public string Name { get; set; }
        public string Latitude { get; set; }
        public string Longitude { get; set; }
    }
}

我需要将位置合并到正确的城市中，并一次性返回上面的整个结构。例如。

// this gets data including city (but no location) :
var country = await _serviceRequestA.GetCountryData();

// get list of Ids to make second call:
var ids = country.States.SelectMany(x => x.Cities).Select(x => x.Id).ToList();

// get list of location objects based on these ids:
var locations = await _serviceRequestB.GetLocations(ids); 

尝试：通过城市将每个城市与每个位置进行匹配。ID 和位置。ItemId，找到后，将位置的 Id、Name、Latitude、Longitude 作为 Location 对象附加到城市。

// do something like this on each city:
// ...but all previous data,
cities.ForEach(c =>
 {
  c.Location = locations.Where(x => x.ItemId == c.Id)
  .FirstOrDefault();
 });

但是，我如何按原样获取每个父对象和子对象，包括城市？

同样，我的数据是：.country.states[n].cities[n]

我对 C# 或 LINQ 没有经验，除了简单的 where 和 selects。我是否必须进行多个循环并获取每个关卡的道具，然后应用合并逻辑？在 LINQ 中是否有更简洁的方法？

PS-这是当前从第一个服务调用返回的内容的json表示，另一个是合并后我想要的结果。我需要将 Location 对象附加到每个匹配的城市：

{
  "country": {
    "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
    "name": "US",
    "states": [
      {
        "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
        "name": "California",
        "cities": [
          {
            "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
            "name": "LA"
          }
        ]
      },
      {
        "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
        "name": "Maine",
        "cities": [
          {
            "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
            "name": "Bangor"
          }
        ]
      }
    ]
  }
}

因此，当我将数据返回到前端时，城市将如下所示：

{
  "country": {
    "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
    "name": "US",
    "states": [
      {
        "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
        "name": "California",
        "cities": [
          {
            "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
            "name": "LA",
            "location": {
               "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
               "name": "Location X",
               "latitude": "xxx",
               "longitude": "xx-xx"
              }
          }
        ]
      },
      {
        "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
        "name": "Maine",
        "cities": [
          {
            "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
            "name": "Bangor",
            "location": {
               "id": "3fa85f64-5717-4562-b3fc-2c963f66afa6",
               "name": "Location Y",
               "latitude": "yy",
               "longitude": "yy-yy"
              }
          }
        ]
      }
    ]
  }
}