使用EF CTP4映射反向关系.... [英] Mapping Inverse relationships using EF CTP4....

问题描述

我正在尝试使用CTP 4支持的实体框架4中的代码优先方法在我的项目中实现数据访问层。

I am trying to implement data access layer in my project using code first approach in Entity Framework 4 which is supported by CTP 4.

首先，我决定尝试使用Northwind示例数据库。

To start with I decided to try my hands on Northwind sample database.

我创建了2个类"类别"。和"产品"如下所示。

I created 2 classes "Category" and "Product" as following.

 

public class Category : EntityBase
 {
 public virtual string CategoryName { get; set; }

 public virtual string Description { get; set; }

 public double? TestColumn { get; set; }

 private ICollection<Product> _products;

 public virtual ICollection<Product> Products
 {
  get { return _products; }
  set { _products = value; }
 }

 public Category()
 {
  _products = new List<Product>();
 }
 }

 public class Product : EntityBase
 {
 public string ProductName { get; set; }

 public int SupplierID { get; set; }

 public string QuantityPerUnit { get; set; }

 public Decimal UnitPrice { get; set; }

 public Int16 UnitsInStock { get; set; }

 public Int16 UnitsOnOrder { get; set; }

 public Int16 ReorderLevel { get; set; }

 public bool Discontinued { get; set; }

 public virtual Category Category { get; set; }
 }

 

对于这些类，我创建了映射类来覆盖默认约定，如下所示。

For these classes I created mapping classes to override the default conventions as following.

public 
class
 CategoryMapping : EntityConfiguration<Category>
 {
 public
 CategoryMapping()
 {
  HasKey(c => c.Id);
  Property(c => c.Id).IsIdentity();
  Property(c => c.CategoryName).IsRequired().HasMaxLength(15);
  Property(c => c.Description);
  
  HasMany(c => c.Products).WithRequired(p =>p.Category);

  MapSingleType(c => new 
{ CategoryID = c.Id, c.CategoryName, c.Description}).ToTable("dbo.Categories"
);
 }
 }

 public 
class
 ProductMapping : EntityConfiguration<Product>
 {
 public 
ProductMapping()
 {
  HasKey(p => p.Id);
  Property(p => p.Id).IsIdentity();
  Property(p => p.ProductName).IsRequired().HasMaxLength(40);
  Property(p => p.SupplierID);
  Property(p => p.QuantityPerUnit).HasMaxLength(20);
  Property(p => p.UnitPrice);
  Property(p => p.UnitsInStock);
  Property(p => p.UnitsOnOrder);
  Property(p => p.ReorderLevel);
  Property(p => p.Discontinued);
  
  HasRequired<Category>(p => p.Category).WithMany(c => c.Products);

  MapSingleType(p => new
 { ProductID = p.Id, p.ProductName, CategoryID = p.Category.Id, p.SupplierID, p.QuantityPerUnit, p.UnitPrice, p.UnitsInStock, p.UnitsOnOrder, p.ReorderLevel, p.Discontinued }).ToTable("dbo.Products"
);
 }
 }

推荐答案

您可能希望切换延迟加载，以便在尝试访问时从数据库中检索给定产品的类别;

It looks like you probably want to switch lazy loading on so that the Category for a given product is retrieved from the database when you try to access it;

objectContext.ContextOptions.LazyLoadingEnabled = true;

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