entity-framework - 在 Entity Framework v1 中添加和更新外键

Question

我正在使用 .NET 3.5 SP1。我创建了实体 'Category'，基于表 'category_table' 和 'MyUser'，基于表 'App_User_table'。

CREATE TABLE category_table (
 catg_id int,
 catg_name varchar(50),
 catg_description varchar(250)
 )

CREATE TABLE App_User_table (
 userid int,
 username varchar(50),
 fullname varchar(50), catg_id int,
 fullAddress varchar(200),
 comments varchar(1000),CONSTRAINT FK_1 FOREIGN KEY (catg_id) REFERENCES Category_table (catg_id) 
)

public class Category: System.Data.Objects.DataClasses.EntityObject{    
 public int  CategoryId{get; set;}   
 public string CategoryName {get; set;} 
  ....
}

public class AppUser : System.Data.Objects.DataClasses.EntityObject{   
 public int Uid {get; set;}   
 public string UserName {get; set;}   
 public string Name {get; set;}   
 public string Address {get; set;}
 public string Comment {get; set;} 
 public Category category_table  { .. } 
 public System.Data.Objects.DataClasses.EntityReference<Category> category_tableReference {...}
 ...........   
}

---

我想在 ASP.NET MVC 应用程序中添加和更新 AppUser 实体。

添加:

//create entity with passed values
AppUser user = new AppUser(){Uid=id, ....  }
//Set EntityReference
user.category_tableReference.EntityKey = new System.Data.EntityKey("MyContext.CategorySet", "CategoryId", categoryIdSelected);
myContext.AddToCategorySet(user);
myContext.SaveChanges(true);

更新:

//create entity with passed Id 
AppUser user = new AppUser(){Uid=id  }
//Attach entitymyContext.AttachTo("UserSet", user);
//Update entity with passed values
user.Address = addr;
....

//从DropDownList更新选择的CategoryId

user.category_tableReference.EntityKey = new System.Data.EntityKey("MyContext.CategorySet", "CategoryId", categoryId);

Update 方法不会更新数据库中的 CategoryId。

请告知，解决问题的最佳方法是什么？

谢谢。

Answer 1

这是我在 MVC 应用程序中用于更新的方法:

// Put the original Stub Entities for both the original User and its 
// original category. The second part is vital, because EF needs to know 
// original FK values to successfully do updates in 3.5 SP1
AppUser user = new AppUser {
    Uid = id, 
    Category = new Category {
        CategoryId = OriginalCategoryID
    }
};
ctx.AttachTo("UserSet", user);

// Then do this:
if (user.Category.CategoryId != categoryIdSelected)
{
    Category newCategory = new Category {CategoryId = CategoryIdSelected};
    // Attach because I assume the category already exists in the database
    ctx.AttachTo("CategorySet", newCategory);
    user.Category = newCategory;
}

// Update entity with passed values
user.Address = addr;
....

正如您所见，您需要能够从某个地方获取 OriginalCategoryID，我建议在表单上设置一个隐藏字段。

这将完成您需要的一切。查看 Tip 26 - How to avoid database queries using Stub Entities有关 Stub Entity 技巧的更多信息。

希望对你有帮助

亚历克斯