Entity Framework查詢ManyToMany關係時遇到的問題

Question

我有三個實體類。

public partial class Person 
{ 
    public Person() 
    { 
     this.Locations = new HashSet<Location>();   
    }  
    public int PersonID { get; set; } 
    public string Name { get; set; } 
    public virtual ICollection<Location> Locations { get; set; }  
} 

public partial class Location 
{  
    public Location() 
    {    
     this.People = new HashSet<Person>(); 
    } 

    public int LocationID { get; set; } 
    public string AddressLine1 { get; set; } 
    public string AddressLine2 { get; set; } 
    public int CityID { get; set; }   
    public virtual City City { get; set; }      
    public virtual ICollection<Person> People { get; set; } 
} 

public partial class City 
{ 
    public City() 
    { 
     this.Locations = new HashSet<Location>(); 
    }  
    public int CityID { get; set; } 
    public string Name { get; set; }       
    public virtual ICollection<Location> Locations { get; set; } 
} 

我想查詢我的實體並獲取給定人員的所有位置。 到目前爲止，我有這種方法。

public IQueryable<Person> GetLocationsForPerson(int id) 
    { 
     return context.People 
       .Include(p => p.Locations) 
       .Where(p => p.PersonID == id); 

    } 

這是工作正常。問題是，我想獲得每個位置的城市的名稱了。當我從Location表中獲取cityID時，Location實體的City屬性返回null。爲什麼是空？以及如何修改我的查詢以獲取城市名稱？任何提示將不勝感激。

Answer 1

替換：

.Include(p => p.Locations) 

有了：

.Include(p => p.Locations.Select(l => l.City)) 

在EF核心也做：

.Include(p => p.Locations) 
    .ThenInclude(l => l.City)