LINQ查詢與3級

Question

我有一個業務對象的結構是這樣的：

國家有美國，國家有城市

所以Country[2].States[7].Cities[5].Name將New York

好吧，我需要得到列表所有至少有1個國家/地區對象City.IsNice == true

我該如何獲得？

Answer 1

var selectedCountries = 
    countries.Where(
     co => co.States.Any(
      s => s.Cities.Any(
       ci => ci.IsNice))); 

另一種選擇：

var selectedCountries = 
    countries.Where(
     co => co.States.SelectMany(s => s.Cities).Any(
      ci => ci.IsNice)); 

Answer 2

var result = (from country in db.Countries 
      from state in country.States 
      from city in state.Cities 
      where city.IsNice 
      select county).Distinct(); 

Answer 3

我會做它的兩種方法之一：

var selectedCountries = from country in countries 
         from state in country.States 
         from city in state.Cities 
         where city.IsNice 
         select country; 

或

var selectedCountries = 
    countries.Where(country => 
        country.States.FirstOrDefault(state => 
                state.Cities.FirstOrDefault(city => 
                       city.IsNice) != null) != null); 

Answer 4

var result = Countries 
    .SelectMany(a => a.States) 
    .SelectMany(b => b.Cities) 
    .Where(b => b.IsNice == true) 
    .ToList();