c# - asp.net MVC 中的 lambda 表达式

Question

我正在尝试从模型中选择特定的列，但是当我尝试为子实体包含选择时出现错误。我的模型是 -

public class Alert
{
    [Key]
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid AlertId { get; set; }

    [Display(Name = "Title"), MaxLength(160, ErrorMessage ="Title cannot be more than 200 characters long."), Required(ErrorMessage ="You must enter an alert title")]
   // [DataType(DataType.MultilineText)]
    public string Title { get; set; }


    [Display(Name = "Description"), MaxLength(8000, ErrorMessage = "Title cannot be more than 8000 characters long."), Required(ErrorMessage ="You must enter a description in {0} field")]
    [AllowHtml]
    [DataType(DataType.MultilineText)]
    public string Description { get; set; }

   [Display(Name = "Start Date"), Required(ErrorMessage ="You must enter the start date and time")]
   [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy hh:mm tt}", ApplyFormatInEditMode = false)]
  // [DataType(DataType.DateTime)]
    public DateTime StartDate { get; set; }

    [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy hh:mm tt}", ApplyFormatInEditMode = false)]
    [Display(Name = "End Date")]
    public DateTime? EndDate { get; set; }

    [Display(Name = "Affected Site/s"), MaxLength(200,ErrorMessage ="You cannot enter more than 200 characters.")]
    public string SitesAffected { get; set; }


    [MaxLength(10)]
    public string Published { get; set; }

    [Display(Name = "Website Link"), MaxLength(200,ErrorMessage ="This cannot be more than 200 characters.")]
    public string WebLink { get; set; }


    [Display(Name ="Alert Type")]
    public int AId { get; set; }

    public virtual ICollection<Location> Location { get; set; }
    public virtual ICollection<AlertFile> Files { get; set; }
    [JsonIgnore]
    public virtual AlertType alertType {get; set;}

}

我可以使用以下 lambda 表达式通过 Web API 生成 json 数据。

var alerts = db.Alerts.Where(a=>a.alertType.Slug== alert && a.EndDate>=DateTime.Now && a.Published=="Yes").Select(s=>new
        {s.Title, s.Description, s.alertType.Slug, s.StartDate, s.EndDate, s.Location
        });


        return Request.CreateResponse(HttpStatusCode.OK, alerts.ToList());

以上代码显示位置表中的所有列。我想显示位置表中的特定列，我尝试了以下代码但出现错误。

var alerts = db.Alerts.Where(a=>a.alertType.Slug== alert && a.EndDate>=DateTime.Now && a.Published=="Yes").Select(s=>new
        {s.Title, s.Description, s.alertType.Slug, s.StartDate, s.EndDate, s.Location.Select(l => new Location { l.Name, l.Latitude, l.Longitude, l.ParkId, l.Contact })
        });

Error: Invalid anonymous type member declarator. Anonymous type members must be declared with a member assignment, simple name or member access.

基本上位置不允许我使用 select 子句。谁能帮忙解决这个问题。提前致谢。

Answer 1

用这一行:

s.Location.Select(l => new Location { l.Name, l.Latitude, l.Longitude, l.ParkId, l.Contact }

您不会将您的值分配给任何属性，如果您想将您选择的列表分配给@Stephen Muecke 说您应该写的属性，您只需选择它:

Location = s.Location.Select(l => new Location { l.Name, l.Latitude, l.Longitude, l.ParkId, l.Contact }

实际上您的完整查询应该如下所示:

var alerts = db.Alerts.Where(a=>a.alertType.Slug== alert && a.EndDate>=DateTime.Now && a.Published=="Yes").Select(s=>new
        { 
            Title = s.Title, 
            Description = s.Description, 
            AlertType = s.alertType.Slug, 
            StartDate = s.StartDate, 
            EndDate = s.EndDate, 
            Location = s.Location.Select(l => new Location { l.Name, l.Latitude, l.Longitude, l.ParkId, l.Contact })
        });

但是 C# 编译器知道如何命名简单的属性。