Question

有两个班级

事件

public class Event 
{

    public Guid? UserID { get; set; }

    [ForeignKey("UserID")]
    public virtual User User { get; set; }
...

用户

 public class User
{
    public Guid UserId { get; set; }
    // Not used in this example, but just thought they might be related to problem
    private List<Event> _attendedEvents;
    public virtual ICollection<Event> AttendedEvents 
    {
        get { return _attendedEvents ?? (_attendedEvents = new List<Event>()); }
        set {
            if (value == null)
                _attendedEvents = new List<Event>();
            else
                _attendedEvents = new List<Event>(value);
        } 
    }
    public virtual ICollection<Event> HostedEvents { get; set; }
...

EventConfiguration

HasOptional<User>(s => s.User)
    .WithMany(s => s.HostedEvents)
    .HasForeignKey(s => s.UserID);

我想做的事是
将用户添加到存储库
将事件（其中包含相同的用户）添加到存储库
保存更改
从存储库中检索事件

一切都有效，除非我检索事件回来时它有空用户，但UserId有效并指向我之前创建的用户。

以下是我正在做的事情

// Creates just the User object with specified UserName
var user = ObjectHelpers.CreateUser("ServiceTestUser");

// Adds to Repository + Saves Changes
_client.AddUser(user);

// Find it again to have generated Id and kind of test if it was added
user = _client.FindUserByEmail(user.Email);

// Create Event object and assign specified user object to it
// At this point @event has User set to above one and UserID null
            var @event = ObjectHelpers.CreateEvent(user);

// Attach User from Event + Add Event to repository + Save Changes
_client.AddEvent(@event);

// Get it back to Check if everything went fine
// At this point @event has User set to null and valid UserID
@event = _client.GetEventByTitle(@event.EventTitle);

Answer 1

默认情况下，EF不会读取相关实体。这种行为非常有用。如果没有，每当你试图从数据库中读取一个实体时，你就会读到那个实体，以及所有可能非常大的相关实体树。

您必须阅读已实体化的实体：

明确地使用.Include()
或隐式地，通过使用延迟加载，这意味着访问导航属性，但DbContext尚未被处理

Include()的示例：

DbCtx.Events.First(ev => ev.Title == "title").Include(ev => ev.User);

有关包含相关实体的详细信息，请参阅：Loading Related Entities

EF一对多检索外键但不检索对象

1 个答案: