我想在entityframework5 codefirst方式上用我的entites创建一个DbContext.我有品牌,类别和产品.
但是当我尝试获取产品时,它的品牌和类别字段为空.类别是可选的,但品牌不是.所以至少必须设置品牌领域.我试过下面的代码.有什么我想念的吗？
public DbSet<Brand> Brands { get; set; }
public DbSet<Product> Products { get; set; }
public DbSet<Category> Categories { get; set; }
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Entity<Brand>()
.HasMany(b => b.Products)
.Withrequired(p => p.Brand)
.HasForeignKey(p => p.BrandId);
modelBuilder.Entity<Category>()
.HasMany(c => c.Products)
.WithOptional(p => p.Category)
.HasForeignKey(p => p.CategoryId);
}
在MVC控制器方面：
using (var db = new InonovaContext())
{
var product = db.Products.Single(p => p.Id == id);
model.Description = product.Description;
model.ImageUrl = product.ImageUrl;
model.Name = product.Name;
model.BreadCrumb = product.Brand.Name + " / " + product.Category == null ? "" : (product.Category.Name + " / ") + product.Name; // Here Brand and Category are null
}
产品类如下
public class Product
{
public int Id { get; set; }
public int BrandId { get; set; }
public virtual Brand Brand { get; set; }
public string Name { get; set; }
public int? CategoryId { get; set; }
public virtual Category Category { get; set; }
public string ImageUrl { get; set; }
public string Description { get; set; }
}
品牌类如下：
public class Brand
{
public int Id { get; set; }
public string Name { get; set; }
public string ThumblogoImageUrl { get; set; }
public string Description { get; set; }
public ICollection<Product> Products { get; set; }
}
谢谢.
解决方法
如果您尚未将品牌和类别声明为虚拟,则延迟加载品牌和类别属性将不起作用.
public class Product
{
public int Id { get; set; }
public string Name { get; set; }
public virtual Brand Brand { get; set; }
public int BrandId { get; set; }
public virtual Category Category { get; set; }
public int? CategoryId { get; set; }
}
有关延迟和急切加载的更多信息,请参阅this.
