xxx.Find()
xxx.First()
xxx.ToArray()
...
https://www.zhihu.com/question/388290065
Entity Framework Code First中能夠自動調用DbContext.ChangeTracker.DetectChanges的方法：
◊ DbSet.Add
◊ DbSet.Find
◊ DbSet.Remove
◊ DbSet.Attach
◊ DbSet.Local
◊ DbContext.SaveChanges
◊ DbContext.GetValidationErrors
◊ DbContext.Entry
◊ DbChangeTracker.Entries
◊ 任何在DbSet上進行LINQ的查詢
https://blog.csdn.net/u011127019/article/details/53941235
同一個上下文中，更新時，同一實體隻能跟蹤一次，如果再次擷取該對象并且跟蹤，并更新該對象時就會報錯，因為ef無法确定具體那個跟蹤的對象需要被儲存，錯誤如下
The instance of entity type 'UserEntity' cannot be tracked because another instance with the same key value for {'Id'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached. Consider using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values
https://q.cnblogs.com/q/103473/ 此問題中就是Find會跟蹤對象，導緻更新失敗