有没有更好和优化的方法来使用 C# 创建嵌套列表？

Question

我想创建一个基于三个 Enumerable 列表的平面列表。这些列表的数据存储在我的数据库中的三个表中：大陆、国家、城市。 为此，我为每个实体获取 3 个循环，因此如果我添加另一个名为 District 的实体，我需要第四个循环，依此类推。那么有一种方法可以优化我的代码以使用 LooKup 或更简洁的 Linq 语法并提高性能吗？请参阅下面的代码：

大陆

Id  Name            
1   NorthAmerica    
2   Europe

国家

Id  Name              ContinentId        
1   USA               1
2   CANADA            1
3   FRANCE            2
4   ENGLAND           2

国家

Id  Name              CountryId        
1   PARIS             3
2   MONTREAL          2
3   NEW YORK          1
4   LYON              3
5   LONDRES           4

在 C# 中，我从存储库中获取每个表的数据

var lists = new List<Select> { };

var continents = _unitOfWork.ContinentRepository.Get().
                 Select(x => new { id = x.Id, name = x.name });

var countries = _unitOfWork.CountryRepository.Get().
                Select(x => new { id = x.Id, continentId = x.ContinentId, name = x.name });

var cities = _unitOfWork.CityRepository.Get().
             Select(x => new { id = x.Id, countryId = x.CountryId, name = x.name });


if (continents.Count() > 0)
{
    foreach (var continent in continents)
    {
        lists.Add(new Select { Id = continent.id, Value = continent.name, Level = "first-level" });
        foreach (var country in countries.Where(x => x.continentId == continent.id))
        {
            lists.Add(new Select { Id =  country.id , Value = country.name, Level = "second-level" });
            foreach (var city in cities.Where(x => x.countryId == country.id))
            {
                lists.Add(new Select { Id = city.id , Value = city.name, Level = "third-level" });
            }
        }
    }
}

NORTHAMERICA
   USA 
     NEW YORK
   CANADA
     MONTREAL
EUROPE
  FRANCE
    LYON
    PARIS
  ...

The class attribute will add the spaces (indentation), so i need it.
[
    {
        "id": 1
        "value": "NorthAmerica",
        "class": "first-level"
    },
    {
        "id": 1
        "value": "USA",
        "class": "second-level"
    },
    {
        "id": 3
        "value": "NEW YORK",
        "class": "third-level"
    },
    {
        "id": 2
        "value": "CANADA",
        "class": "second-level"
    },
    {
        "id": 3
        "value": "MONTREAL",
        "class": "third-level"
    },
    {
        "id": 2
        "value": "Europe",
        "class": "first-level"
    },
    {
        "id": 1
        "value": "FRANCE",
        "class": "second-level"
    },
    {
        "id": 3
        "value": "PARIS",
        "class": "third-level"
    },
    {
        "id": 4
        "value": "LYON",
        "class": "third-level"
    },
    {
        "id": 4
        "value": "ENGLAND",
        "class": "second-level"
    },
        "id": 5
        "value": "LONDRES",
        "class": "third-level"
    },
]

Answer 1

我不知道你为什么在那些有图书馆可以更好地处理这个问题的日子里做这样的事情 EntityFramework 和 EntityWorker.Core

在 Entityworker.Core 中，只需一次选择即可轻松完成 这是您的模块示例

public class Continent {

  [PrimaryKey]
  public int Id { get; set; }

  public string Name { get; set; }

  public List<Country> Countries { get; set; }

}

public class Country {

  [PrimaryKey]
  public int Id { get; set; }

  public string Name { get; set; }

  [ForeignKey(typeof(Continent))]
  public int ContinentId { get; set; }

  public List<City > Cities { get; set; }

}

   public class City {

      [PrimaryKey]
      public int Id { get; set; }

      public string Name { get; set; }


      [ForeignKey(typeof(Country))]
      public int CountryId { get; set; }
  }

现在您所要做的就是获取数据并加载孩子

using (var rep = new Repository())
   {
     // this will load all Continent and Countries and Cities all togather with a single call
    List<Continent> Continents = rep.Get<Continent>().Where(x=> x.Id == 54).LoadChildren().Execute(); 
   }

这里有更多关于图书馆的信息 https://www.codeproject.com/Tips/1222424/EntityWorker-Core-An-Alternative-to-Entity-Framewo

Entityframework 可以做同样的事情，除了 LoadChildren 你做 Include() http://www.entityframeworktutorial.net/basics/context-class-in-entity-framework.aspx