C# Entity Framework Code-First - 如何仅使用外键的 id 添加带有外键的行？

问题描述

如果我有以下类（使用 CodeFirst 实体框架）：

public class Notifications
{
    [Key]
    public int ID { get; set; }
    public virtual ClientDetails Client { get; set; }
    public virtual NotificationTypes NotificationType { get; set; }
    public virtual NotificationFreqs Frequency { get; set; }
    public virtual NotificationStatus Status { get; set; }
    public DateTime SendDate { get; set; }
    public DateTime? SentDate { get; set; }
    public DateTime QueueDate { get; set; }
}

public class NotificationFreqs
{
    [Key]
    public int ID { get; set; }
    [MaxLength(25)]
    public string Name { get; set; }
}

public class NotificationStatus
{
    [Key]
    public int ID { get; set; }
    [MaxLength(25)]
    public string Status { get; set; }
}

添加新通知时，最有效的说 notification.status = 1 方式是什么？ 我是否每次都必须查询数据库才能获得可用列表？

var notification = new Notifications();

var notificationType = db.NotificationTypes.FirstOrDefault(n => n.ID == notificationTypeId);
var notificationFreq = db.NotificationFreqs.FirstOrDefault(n => n.Name == setting.Value);

notification.NotificationType = notificationType; // Works
notification.Frequency = notificationFreq; // Works
notification.Status = new NotificationStatus { ID = 1 };  // ObvIoUsly doesn't work

我觉得多次访问数据库效率低下，但我确实希望这些值标准化并在数据库中。

有什么建议吗，或者我的做法是 NotificationType 和 Frequency 的唯一方法？

谢谢！

解决方法

你必须修复你的课程。添加 ID 字段：

public class Notifications
{
    [Key]
    public int ID { get; set; }
    public virtual ClientDetails Client { get; set; }

    [ForeignKey("NotificationType")]
    public int? Type_ID  { get; set; }
    public virtual NotificationTypes NotificationType { get; set; }

    [ForeignKey("Frequency")]
    public int? Frequency_ID { get; set; }
    public virtual NotificationFreqs Frequency { get; set; }

    [ForeignKey("Status")]
    public int? Status_ID { get; set; }
    public virtual NotificationStatus Status { get; set; }

    public DateTime SendDate { get; set; }
    public DateTime? SentDate { get; set; }
    public DateTime QueueDate { get; set; }
}

在这种情况下：

notification.Type_ID = notificationTypeId; 
notification.Frequency_ID = notificationFreq.ID; 
notification.Status_ID = 1