实体框架查询多个关系故障[重复]

Question

我有三个实体类。

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; }
}

我正在尝试查询我的实体，并获得给定的人的所有位置。到目前为止我有这个方法。

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

    }

问题是我还想为每个地点获得城市的名称。当我从Location表获取cityID时，Location实体的City属性返回NULL。为什么那是空的？我如何修改我的查询以获得城市名称？如有任何提示，将不胜感激。

Answer 1

替换：

.Include(p => p.Locations)

与：

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

在EF Core中，您还可以：

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