比較2名列表內部實體框架Where子句

Question

我有3個實體框架的實體：

public class Tag { 
    public Int32 Id { get; set; } 
    public String Name { get; set; } 
} 

public class Book { 
    public Int32 Id { get; set; } 
    public String Name { get; set; } 
    public IList<Tag> Tags { get; set; } 
} 

public class Post { 
    public Int32 Id { get; set; } 
    public String Name { get; set; } 
    public IList<Tag> Tags { get; set; } 
} 

鑑於一本書，我需要得到所有具有完全相同的標籤作爲書的帖子。

IList<Tags> tags = new List<Tag> { new Tag { Id = 1 }, new Tag { Id = 2 } }; 

Book book = new Book { Tags = tags }; 

context.Posts.Where(x => 
    new HashSet<Int32>(x.Tags.Select(y => y.Id)).SetEquals(book.Tags.Select(y => y.Id))) 
.ToList(); 

我得到以下錯誤：

An exception of type 'System.NotSupportedException' occurred in mscorlib.dll but was not handled in user code 

Additional information: LINQ to Entities does not recognize the method 'Boolean SetEquals(System.Collections.Generic.IEnumerable`1[System.Int32])' method, and this method cannot be translated into a store expression. 

任何想法如何解決這個查詢？

謝謝你， 米格爾

Answer 1

from p in context.Posts 
let tags = context.Books(b=>b.ID == bookId).Select(b=>b.Tags)//you might need .SelectMany 
where p.Tags.All(t=>tags.Any(bt=>bt.Id == t.Id)) 
select p 

只做lambda表達，它可能會更好，在率先拿到標籤，它可能會更好，即使在第一個選項。

var tags = context.Books(b=>b.ID == bookId).Select(b=>b.Tags)//you might need .SelectMany 

var result = context.Posts.Where(p=>p.Tags.All(t=>tags.Any(bt=>bt.Id == t.Id)).ToList(); 

Answer 2

我不知道，如果SequenceEqual工作，LINQ到實體，但你可以看一下。

http://msdn.microsoft.com/en-us/library/bb348567%28v=vs.110%29.aspx