Question

我的实体Person由EF生成。我正在尝试在搜索特定字符时在自动填充文本框中显示名字，就像Facebook搜索一样。当我尝试运行时，我收到错误消息：

The entity or complex type 'Dejtingsajt3.Repositories.Person' cannot be constructed in a LINQ to Entities query.

这是我的.html-page：

中的脚本代码

<script>
    $("#searchInput").autocomplete({
        source: function (request, response) {
            $.ajax({
                url: '@Url.Action("GetSearchValue", "Home")',
                dataType: "json",
                data: { search: $("#searchInput").val() },
                success: function (data) {
                    response($.map(data, function (item) {
                        return { label: item.FirstName, value: item.FirstName };
                    }));
                },
                error: function (xhr, status, error) {
                    alert("Error");
                }
            });
        }
    });
</script>

这是来自控制器的方法：

public class HomeController : Controller
{
    private DataContext dataContext = new DataContext();

    public ActionResult Index()
    {
        return View();
    }

    public JsonResult GetSearchValue(string search)
    {
        List<Person> allSearch = dataContext.User.Where(n => n.FirstName
        .Contains(search)).Select(x => new Person
        {
            FirstName = x.FirstName

        }).ToList();

        return new JsonResult {Data=allSearch, JsonRequestBehavior =
            JsonRequestBehavior.AllowGet };
    }
}

这是我的人事实体：

public class Person
{
    public Person()
    {
        FriendRequestReceive = new HashSet<FriendRequest>();
        FriendRequestSend = new HashSet<FriendRequest>();
        MessageRecieve = new HashSet<Message>();
        MessageSend = new HashSet<Message>();
    }

    [Key]
    public int PersonID { get; set; }

    [Required(ErrorMessage = "A first name is required.")]
    [Display(Name = "First Name")]
    public string FirstName { get; set; }

    [Required(ErrorMessage = "A last name is required.")]
    public string LastName { get; set; }

    [Required(ErrorMessage = "A social number is required.")]
    public string SocialNumber { get; set; }

    [Required(ErrorMessage = "A gender is required.")]
    public string Gender { get; set; }

    [Required(ErrorMessage = "A city is required.")]
    public string City { get; set; }

    [EmailAddress(ErrorMessage = "Please enter a valid email.")]
    public string Mail { get; set; }

    public string ProfilePicture { get; set; }

    public string PresentationText { get; set; }

    public string Preference { get; set; }

    [Required(ErrorMessage = "A username is required.")]
    public string UserName { get; set; }

    [Compare("Password", ErrorMessage = "A password is required")]
    [DataType(DataType.Password)]
    public string Password { get; set; }

    public virtual ICollection<FriendRequest> FriendRequestReceive { get; set; }
    public virtual ICollection<FriendRequest> FriendRequestSend { get; set; }
    public virtual ICollection<Message> MessageRecieve { get; set; }
    public virtual ICollection<Message> MessageSend { get; set; }
    public string FileName { get; internal set; }
    public string ContentType { get; internal set; }
    public byte[] File { get; internal set; }
}

我已经搜索了一个解决方案并尝试了一些不同的方法，但没有任何运气。

Answer 1

问题出现在代码的下一部分：

sympy

如果你试图将项目放到映射的实体上，你基本上做的是部分加载一个实体，这不是一个有效的状态。这就是您无法将查询投影到映射实体的原因。但是，您可以使用DTO：

List<Person> allSearch = dataContext
    .User
    .Where(n => n.FirstName.Contains(search))
    .Select(x => new Person { FirstName = x.FirstName })
    .ToList();

您还有其他2个选项。首先，您可以将查询映射为匿名类型：

// DTO class for projection
public class PersonDTO
{
    public string FirstName { get; set; }
}

// correct query
List<PersonDTO> allSearch = dataContext
    .User
    .Where(n => n.FirstName.Contains(search))
    .Select(x => new PersonDTO { FirstName = x.FirstName })
    .ToList();

此外，您可以使用var allSearch = dataContext .User .Where(n => n.FirstName.Contains(search)) .Select(x => new { FirstName = x.FirstName }) .ToList();课程（如果您需要所有人员的字段），但从查询中移除投影：

Person

Answer 2

您无法创建Person，您必须从数据库中检索。假设User的对象类型为Person，请离开Select：

var allSearch = dataContext.User
                    .Where(n => n.FirstName.Contains(search))
                    .ToList();

实体不能在LINQ to Entities查询中构造

2 个答案: