今天我决定把我的一个老项目从Asp.net核心1.1升级到2.1,一切都很顺利,直到我尝试从数据库中检索一个本地事件列表。我使用的是.AsNotracking,因为除了排序/过滤之外,我不需要对对象进行任何更改。
这是错误:
类型为“System.DateTime”的
表达式不能用于对类型“System.Nullable`1System.DateTime”的赋值
这是我遇到问题的代码:
var today = DateTime.Now;
var events = await _context.LocalEvent.Where
(x => x.ReoccurUntil > today || x.EventEnd > today).AsNoTracking().ToListAsync();
这是LocalEvent模型:
public class LocalEvent
{
[NotMapped]
private DateTime? dateCreated;
[Key]
public Guid Id { get; set; }
[MaxLength(200)]
[Display(Name = "Event Location")]
[DataType(DataType.MultilineText)]
public string Location { get; set; }
[Display(Name = "Added By")]
public string Author { get; set; }
[Display(Name = "Contact")]
public string EventContact { get; set; }
[Display(Name = "Event Name")]
public string EventName { get; set; }
[DataType(DataType.MultilineText)]
[Display(Name = "Details")]
public string EventInfo { get; set; }
[DataType(DataType.Currency)]
[DisplayFormat(DataFormatString = "{0:C0}", ApplyFormatInEditMode = true)]
[Display(Name = "Cost")]
public Decimal? EventCost { get; set; }
//DateStuff
[Display(Name = "Date Created")]
public DateTime DateCreated
{
get { return dateCreated ?? DateTime.Now; }
set { dateCreated = value; }
}
[Display(Name = "Event Start")]
public DateTime EventStart { get; set; }
[DateGreaterThan("EventStart")]
[Display(Name = "Event End")]
public DateTime EventEnd { get; set; }
public DateTime ReoccurUntil { get; set; }
[Display(Name = "Reoccurrence Type")]
public TypeOfOccurrence OccurrenceType { get; set; }
[Display(Name = "Which Occurence of Weekday")]
public Nth NthReOccurence { get; set; }
[Display(Name = "Weekday for Reoccurence")]
public DayOfWeek ReoccurrenceDay { get; set; }
[Display(Name = "Occurrence Rate")]
public OccurrenceRate Occurrence { get; set; }
public bool DoesReoccur { get; set; }
[DataType(DataType.ImageUrl)]
public string Image { get; set; }
public string ImageDeletePath { get; set; }
public string Slug { get; set; }
}
现在,我只是简单地删除了AsNoTracking,让它恢复工作。我做错了什么吗?
这个错误真的很奇怪,因为它提到了日期,所以需要一段时间才能追溯到AsNoTracking,我删除了所有与日期有关的内容,最初只是删除了可以为空的日期,然后我意识到对管理员列表(一个完整的跟踪列表)的类似调用可以与唯一的区别是AsNoTracking一起工作,这就是我(在测试之后)决定在这里询问的时候。
我的想法是,如果我不打算修改、删除等,我应该避免跟踪以提高性能!?
希望有人能在这个问题上提供一点启发!提前感谢!
发布于 2018-06-10 01:16:08
它是由v2.1中引入的EF核心错误引起的。
未提供解决方法,已计划在v2.2中修复。
我可以建议的是强制EF使用属性而不是支持字段:
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
// ...
modelBuilder.Entity<LocalEvent>()
.Property(e => e.DateCreated)
.UsePropertyAccessMode(PropertyAccessMode.Property);
// ...
}
https://stackoverflow.com/questions/50776505
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