我有一个ASP.NET MVC应用程序,它使用Entity Framework来获取数据.
在将它们传递给View之前,我需要将Entites转换为模型.预测可能非常复杂,但要保持简单:
public static IQueryable<usermodel> ToModel(this IQueryable<User> users) { return from user in users select new usermodel { Name = user.Name,Email = user.Email,}; }
这可以在这样的控制器中使用:
return View(Repository.Users.ToModel().ToList());
很好.但是,如果我想在另一个投影中使用这个投影怎么办?例:
public static IQueryable<BlogPostModel> ToModel(this IQueryable<BlogPost> blogs) { return from blogs in blogs select new BlogPostModel { Title = blog.Title,Authors = blog.Authors.AsQueryable().ToModel(),// (entities are POCOs) // This does not work,because EF does not understand method ToModel(). }; }
(假设博客可以有多个作者,而且类型为User).
我可以以某种方式将投影分开并在其他投影中重复使用吗?
解决方法
这里有一些实际工作(在一个简单的测试应用程序中),只选择请求的字段:
namespace Entities { public class BlogPost { public virtual int Id { get; set; } public virtual string Title { get; set; } public virtual DateTime Created { get; set; } public virtual ICollection<User> Authors { get; set; } } public class User { public virtual int Id { get; set; } public virtual string Name { get; set; } public virtual string Email { get; set; } public virtual byte[] Password { get; set; } public virtual ICollection<BlogPost> BlogPosts { get; set; } } } namespace Models { public class BlogPostModel { public string Title { get; set; } public IEnumerable<usermodel> Authors { get; set; } } public class usermodel { public string Name { get; set; } public string Email { get; set; } } public static class BlogPostModelExtensions { public static readonly Expression<Func<BlogPost,BlogPostModel>> ToModelConverterExpression = p => new BlogPostModel { Title = p.Title,Authors = p.Authors.AsQueryable().Select(usermodelExtensions.ToModelConverterExpression),}; public static readonly Func<BlogPost,BlogPostModel> ToModelConverterFunction = ToModelConverterExpression.Compile(); public static IQueryable<BlogPostModel> ToModel(this IQueryable<BlogPost> blogPosts) { return blogPosts.Select(ToModelConverterExpression); } public static IEnumerable<BlogPostModel> ToModel(this IEnumerable<BlogPost> blogPosts) { return blogPosts.Select(ToModelConverterFunction); } } public static class usermodelExtensions { public static readonly Expression<Func<User,usermodel>> ToModelConverterExpression = u => new usermodel { Name = u.Name,Email = u.Email,}; public static readonly Func<User,usermodel> ToModelConverterFunction = ToModelConverterExpression.Compile(); public static IQueryable<usermodel> ToModel(this IQueryable<User> users) { return users.Select(ToModelConverterExpression); } public static IEnumerable<usermodel> ToModel(this IEnumerable<User> users) { return users.Select(ToModelConverterFunction); } } }
要测试它而不实际创建数据库:
var blogPostsQuery = ( from p in context.BlogPosts where p.Title.StartsWith("a") select p).ToModel(); Console.WriteLine(((ObjectQuery)blogPostQuery).ToTraceString());