ASP.NET-如何与实体框架进行内部联接

不知道你的模式,我无法给出具体的答案,但是 Join() ,您需要提供:

IEnumerable<TInner> inner -这是你想要加入的 到 .

Expression<Func<TOuter, TKey>> outerKeySelector -这是如何从要加入的内容中指定字段的方法 从 .

Expression<Func<TInner, TKey>> innerKeySelector -这是您如何指定要加入的字段的方式-来自 TInner 先前定义。

Expression<Func<TOuter, TInner, TResult>> resultSelector -这是您将从加入中返回的内容。

例如,此SQL查询:

SELECT i.*
FROM Outer o JOIN Inner i ON o.SomeId = i.SomeId
WHERE o.SomeValue < 5

可以用 连接() 像:

var result = outers.Where(o => o.SomeValue < 5)
                 .Join(inners, o => o.SomeId, i => i.SomeId, (o, i) => i);

实体框架使用配置来反映相关实体之间的关系。给定实体,如:

public class BlogClass
{
   public int Id {get; set;}
   public string Title {get; set;}
   public string Post {get; set;}
   public DateTime Date {get; set;}
   public string FeaturedImage {get; set;} // Assuming a URL?

   public virtual ClassCategory Category {get;set;}
}

public class ClassCategory
{
   public int Id {get; set;}
   public string Category {get; set;}
   // Other properties...
}

我们可以设置配置:

public class BlogClassConfiguration : EntityTypeConfiguration<BlogClass>
{
   public BlogClassConfiguration()
   {
      ToTable("BlogClasses");
      HasKey(x => x.Id)
         .Property(x => x.Id)
         .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity); // Assuming the ID's are set up as identity or have defaults.

      HasRequired(x => x.Category)
         .WithMany()
         .Map(x => x.MapKey("Category")); // This maps our CategoryClasses reference (Category) to a column on the BlogCategories table called "Category".
   }
}
Public class ClassCategoryConfiguration : EntityTypeConfiguration<ClassCategory>
{
   public ClassCategoryConfiguration()
   {
      ToTable("CategoryClasses");
      HasKey(x => x.Id)
         .Property(x => x.Id)
         .HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
   }
}

我们告诉dbContext在构建模型时加载这些配置:

public class BlogDbContext : DbContext
{
   public DbSet<BlogClass> BlogClasses {get; set;}

   public BlogDbContext(string connectionString)
      : base (connectionString)
   {}

   protected override void OnModelCreating(DbModelBuilder modelBuilder)
   {
      base.OnModelCreating(modelBuilder);

 modelBuilder.Configurations.AddFromAssembly(typeof(TestDbContext).Assembly);
   }
}

然后,ef完全管理连接。

var categoryName = category.Replace("_", " ");

using (var context = new BlogContext("BlogConnectionString"))
{
   var blogs = context.BlogClasses
      .Where(x => x.Category.Category == categoryName)
      .OrderByDescending(x => x.Date)
      .ToList(); // Assumes not too many items returned!
}

此示例将dbContext作为示例范围。理想情况下,这应该由IOC容器管理并作为依赖项提供。