爲什麼EF在FirstOrDefault調用（EF6）後沒有從DB返回實體？

我有一些代碼（比這個例子更復雜的），我不明白爲什麼FirstOrDefault通話，這清楚地往返於DB，是不是從數據庫返回一個新的實體：爲什麼EF在FirstOrDefault調用（EF6）後沒有從DB返回實體？

var dbContext = new MyDBContext(); 

// this will not round-trip to Db if found in context 
var user = this.dbContext.EFUsers.Find(someUID); 

// some other work here with 'user' 

this.dbContext.ObjectContext.Detach(user); 

// stuff in disconnected mode 
var newUser = new EFUser() { UID = someUID }; 
// stuff in disconnected mode 

this.dbContext.EFUsers.Attach(newUser); 

// finish working with newUser 
// (eg. deletion of many-to-many relation to avoid loading related entities in memory) 

user = this.dbContext.EFUsers.FirstOrDefault(us => us.UID == someUID); 

// I would expect at this point that 'user' will be queried with fresh values from DB, 
// In reality, I get back only the entity with UID filled in, 'newUser' from above 


// some update user goes here which fails because of the above 

dbContext.SaveChanges();

我認爲Find將從上下文返回給我用戶（如果可用），但FirstOrDefault始終是具有來自數據庫的新值的用戶。

任何人都可以解釋一下嗎？我將如何克服這種影響？

來源

2014-04-03 Learner