实体框架代码返回空字段的第一个导航属性 [英] Entity Framework Code First navigational properties returning null fields

问题描述

对于程序，我第一次使用EF代码。在过去我使用linq到SQL en EF DbFirst。当检索主记录时，我无法使用导航属性加载子记录。我得到一个空的子记录，所有记录字段为0或为空。

For a program I'm using EF code first for the first time. In the past I used linq to SQL en EF DbFirst. When retreiving the main record'I'm unable to load the subrecords using the navigational properties. I get an empty subrecord with all record-fields are 0 or null.

当我想要加载加载。我已经设置了以下类：

When I want to apply eager loading. the .Include(x=>x.......) isn't showing my navigationals.

I have set up the following classes:

public Record()
    {
        Shipping = new ShippingData();
        Delivery = new DeliveryData();
        Items = new List<Item>();
        ImportDate = DateTime.Now;
    }

    [Key]
    public int RecordId { get; set; }
    public int ShippingId { get; set; }
    public int DeliveryId { get; set; }
    public DateTime ImportDate { get; set; }

    public virtual ShippingData Shipping { get; set; }
    public virtual DeliveryData Delivery { get; set; }
    public virtual List<Item> Items { get; set; }
    public virtual Collecting CollectingOrder { get; set; }

与以下上下文：

public class TweemansContext : DbContext
{
    public TweemansContext()
        : base("xxxx")
    {
    }

    public DbSet<Add.Record> Records { get; set; }
    public DbSet<Add.ShippingData> Shipping { get; set; }
    public DbSet<Add.DeliveryData> Delivery { get; set; }
    public DbSet<Add.Item> ProductItems { get; set; }
    public DbSet<Add.Kolli> Kolli { get; set; }
    public DbSet<Add.Collecting> CollectingOrders { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        base.OnModelCreating(modelBuilder);
        modelBuilder.Entity<Record>().HasRequired(s => s.Shipping)
                    .WithMany()
                    .HasForeignKey(s => s.ShippingId);
        modelBuilder.Entity<Record>().HasRequired(d => d.Delivery)
                    .WithMany()
                    .HasForeignKey(d => d.DeliveryId);
        modelBuilder.Entity<Record>().HasOptional(c => c.CollectingOrder)
                    .WithOptionalDependent(a => a.Record).Map(p => p.MapKey("CollectionID"));
    }
}

交付类是一个公共类，如下：

the delivery class is a public class as wel as follows:

    public class DeliveryData
{
    [Key]
    public int DeliveryId { get; set; }
    public virtual Record Record { get; set; }

    ....lots of public properties

使用延迟加载我的所有属性的交付类都是null使用以下代码：

now when I try to use lazy loading all my properties of the delivery class are null using the following code:

using (TweemansContext context = new TweemansContext())
        {
            var imported = (from record in context.Records
                            where record.ImportDate.Year == date.Year && record.ImportDate.Month == date.Month && record.ImportDate.Day == date.Day
                            select record).ToList();

            foreach (var Record in imported)
            {
                string email;
                string telnr;
                CustomerService service = new CustomerService(connectionString);
                **string servicenr = Record.Delivery.AccountNumber.Substring(2, 8);**
                service.GetUserData(servicenr, out email, out telnr);
                Record.Delivery.Email = email;
                Record.Delivery.TelephoneNbr = telnr;
            }
            context.SaveChanges();
        }

在我的调试器的行上告诉我交付存在，所有的属性都为null。

on the rows with the ** my debugger is telling me that delivery exists but all of it's properties are null.

如果要应用include，则.include不显示导航：

When wanting to apply an include as follows the .include isn't showing my navigation:

    var imported = (from record in context.Records.Include(x=>x.)
                            where 
                               record.ImportDate.Year == date.Year 
                               && record.ImportDate.Month == date.Month
                               && record.ImportDate.Day == date.Day
                            select record).ToList();

我做错了什么，或者哪个部分我误入了？

What am I doing wrong, or which part have i misuderstood??

推荐答案

您必须从记录中删除导航引用的初始化构造函数，空导航集合的初始化可以：

You must remove the initialization of the navigation references from the Record constructor, the initialization of the empty navigation collection is OK:

Shipping = new ShippingData(); // remove this line
Delivery = new DeliveryData(); // remove this line

本质上这些行将加载数据与 code> ShippingData 和 DeliveryData 设置，可能是默认值 0 和 null 。

Essentially these lines "overwrite" the loaded data with values that the constructors of ShippingData and DeliveryData set, probably the default values 0 and null.

关于你的评论的旁注.include（x => x .... ...）没有显示我的导航。您需要使用System.Data.Entity; 在代码文件的开头放置，使 Include 扩展方法可以使用lambda表达式作为参数。

Side note about your remark "the .Include(x=>x.......) isn't showing my navigationals". You need to put using System.Data.Entity; at the beginning of your code file to make the Include extension method available that takes a lambda expression as parameter.

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