實體框架導航屬性爲null

Question

我有2個簡單的類：

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; } 
} 

當我從數據庫中檢索集合設置總是空一個SettingCategory。

當我讓它virtual然後它會說：The ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

如何訪問我的Settings名單？

如果我從數據庫中檢索Setting，則會填充SettingCategory屬性，反之亦然。

這是我最初的代碼遷移腳本：

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); 

這是得到它從數據庫中部分：

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

回答

我忘了包括在.SettingCategories，但我試着用拉姆達：

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

這並不工作，但這樣做：

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

Answer 1

因爲你處置您的BackofficeContext不能使用惰性加載，這是當你Settings虛擬發生了什麼。

您可以延長BackofficeContext的使用期限或迫切加載Settings。您可以使用Include進行熱切加載。

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