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[ASP.net教程]EntityFrameWork Code First 多对多关系处理


场景2: 一个文章类别(Category)下含有多篇文章(Article),而文章也可能对应多个类别

Article和Category的代码更改如下:

/// <summary>/// 文章信息/// </summary>public class Article:ModelBase{  /// <summary>  /// 类别名字  /// </summary>  public string Name { get; set; }  public ICollection<Category> Categorys { get; set; }}

 

public class Category : ModelBase{  /// <summary>  /// 类别名字  /// </summary>  public string Name { get; set; }  public ICollection<Article> Articles { get; set; }}


然后在Entity Framework的OnModelCreating中通过Fluent API定义“多对多”关系
如下配置会在数据库生成一张叫ArticleCategory的表属性分别为ArticleID和CategoryID

public class CmsDbContext : DbContextBase{  public CmsDbContext():base(CachedConfigContext.Current.DaoConfig.Cms,new LogDbContext()) {       }  protected override void OnModelCreating(DbModelBuilder modelBuilder)  {    Database.SetInitializer<CmsDbContext>(null);    modelBuilder.Entity<Article>().HasMany(a => a.Categorys)      .WithMany(c => c.Articles)      .Map(u =>      {        u.MapLeftKey("ArticleID");        u.MapRightKey("CategoryID");        u.ToTable("ArticleCategory");                });    base.OnModelCreating(modelBuilder);  }  public DbSet<Category> Categorys { get; set; }  public DbSet<Article> Articles { get; set; }}


分别编写两个场景来测试以下结果:

public interface ICmsService{  //通过文章id获取文章同时加载该文章所有类别信息  Article GetArticle(int articleId);  //通过类别id获取类别同时加载该类别下所有文章  Category GetCategory(int categoryId);}


接口实现类:

public class CmsService : ICmsService{  public Article GetArticle(int articleId)  {    using (var dbContext = new CmsDbContext())     {      return dbContext.Articles.Include("Categorys").FirstOrDefault(a => a.ID == articleId);    }  }  public Category GetCategory(int categoryId)  {    using (var dbContext = new CmsDbContext())     {      return dbContext.Categorys.Include("Articles").FirstOrDefault(c => c.ID == categoryId);    }  }}


这里使用ASP.NET MVC来显示结果,在View中传入的model可以在视图的Model对象直接获取数据(需要在视图页指定类型)

public class ArticleController: AdminControllerBase{  public ActionResult Index()   {    var models = this.CmsService.GetArticle(1);    return View(models);  }}


Razor视图页编写如下:

@model Qxun.Cms.Contract.Article<h2>显示文章的所有类型</h2>@if (Model!=null) {  @Model.Name<br/>  foreach (var item in Model.Categorys)   {    <span>@item.Name</span><span>|@item.CreateTime</span> <br/>     }}


通过下面的结果发现,已经把文章相关的类别加载进来了。通过类别加载文章原理是一样的,就不再写一遍了。