实体框架导航属性为null

Question

我有2个简单的类:

public class Setting
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid SettingId { get; set; }

    [Required]
    public String Name { get; set; }

    public String Value { get; set; }

    [Required]
    public SettingCategory SettingCategory { get; set; }
}

public class SettingCategory
{
    [Key, DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public Guid SettingCategoryId { get; set; }

    [Required]
    public String Value { get; set; }

    public ICollection<Setting> Settings { get; set; }
}

当我SettingCategory从数据库中检索a时,集合Settings始终为null.

当我做它virtual然后会说:The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

我怎样才能访问我的Settings列表？

另一种方式是工作,如果我Setting从数据库中检索SettingCategory属性已填充.

这是我最初的代码迁移脚本:

CreateTable(
    "dbo.Settings",
    c => new
        {
            SettingId = c.Guid(nullable: false, identity: true),
            Name = c.String(nullable: false),
            Value = c.String(),
            SettingCategory_SettingCategoryId = c.Guid(nullable: false),
        })
    .PrimaryKey(t => t.SettingId)
    .ForeignKey("dbo.SettingCategories", t => t.SettingCategory_SettingCategoryId, cascadeDelete: true)
    .Index(t => t.SettingCategory_SettingCategoryId);

CreateTable(
    "dbo.SettingCategories",
    c => new
        {
            SettingCategoryId = c.Guid(nullable: false, identity: true),
            Value = c.String(nullable: false),
        })
    .PrimaryKey(t => t.SettingCategoryId);

这是从数据库中获取它的部分:

public SettingCategory Get(Guid settingCategoryId)
{
    using (var context = new BackofficeContext())
    {
        return context
            .SettingCategories
            .FirstOrDefault(s => s.SettingCategoryId == settingCategoryId);
    }
}

回答

我忘记了包含.SettingCategories,但我正在尝试使用lambda:

public SettingCategory Get(Guid settingCategoryId)
{
    using (var context = new BackofficeContext())
    {
        return context
            .SettingCategories
            .Include(s => s.Settings)
            .FirstOrDefault(s => s.SettingCategoryId == settingCategoryId);
    }
}

这不起作用,但这样做:

public SettingCategory Get(Guid settingCategoryId)
{
    using (var context = new BackofficeContext())
    {
        return context
            .SettingCategories
            .Include("Settings")
            .FirstOrDefault(s => s.SettingCategoryId == settingCategoryId);
    }
}

Answer 1

因为你正在处理你,所以BackofficeContext你不能使用LazyLoading,这就是Settings虚拟时发生的事情.

您可以增加您的生命周期BackofficeContext或急切负载Settings.您可以使用急切加载Include.

public SettingCategory Get(Guid settingCategoryId)
{
    using (var context = new BackofficeContext())
    {
        return context
            .SettingCategories
            .Include(s => s.Settings)
            .FirstOrDefault(s => s.SettingCategoryId == settingCategoryId);
    }
}