Entity Framework 具有 2 个多对多连接的查询

Question

我正在处理一个首先使用 EF 代码并具有以下模型关系的项目：

Item (Id, Name, virtual List<Category>, virtual List<Tag>)  
Category (Id, Name, virtual List<Item>)  
Tag (Id, Name, virtual List<Item>)

我正在运行进行搜索，我想在其中获取项目名称 = searchTerm、类别 ID 包含在整数列表中以及标签名称存在于列表中的所有项目标签。

public IEnumerable<Item> Search(string searchTerm, IEnumerable<int> categoryIds, IEnumerable<string> tags)
{
    var query = (
        from i in context.Items
        from c in context.Categories
        from t in context.Tags
            where i.Name.Contains(searchTerm)
            && categoryIds.Contains(c.Id)
            && tags.Contains(t.Name)
        select i);

    return query.ToList();
}

在 SQL 中，查询如下所示：

SELECT I.* FROM Items I
INNER JOIN ItemItemCategories IIC ON IIC.Item_Id = I.Id
INNER JOIN ItemCategories C ON C.Id = IIC.ItemCategory_Id
INNER JOIN ItemItemTags IIT ON IIT.Item_Id = I.Id
INNER JOIN ItemTags T On T.Id = IIT.ItemTag_Id
WHERE I.Question like '%sample%' -- searchTerm
AND C.Id in (1,2) -- categoryIds
AND (T.Text like '%Difficult%' OR T.Text like '%Technical%') -- tags

我的问题是如何将我的代码形成为 return 上面的查询。据我所知，这是执行查询的最有效方法。当前正在从代码运行中查询以下查询：

SELECT 
    [Filter1].[Id1] AS [Id], 
    [Filter1].[Name] AS [Name]
    FROM   (
    SELECT 
        [Extent1].[Id] AS [Id1], 
        [Extent1].[Name] AS [Name] 
        FROM  [dbo].[Items] AS [Extent1]
        CROSS JOIN [dbo].[Categories] AS [Extent2]
        WHERE [Extent2].[Id] IN (1, 2) ) AS [Filter1]
        CROSS JOIN [dbo].[Tags] AS [Extent3]
    WHERE ([Filter1].[Name] LIKE @p__linq__0 ESCAPE N'~') AND ([Extent3].[Name] IN (N'Difficult', N'Technical')) AND ([Extent3].[Name] IS NOT NULL)

Answer 1

试试这个：

var query = ( from i in context.Items
              from c in i.Categories
              from t in i.Tags
              where i.Name.Contains(searchTerm) 
              && categoryIds.Contains(c.Id)
              && tags.Contains(t.Name)
              select i).ToList();

您不必搜索所有类别和标签元素，只需搜索与您相关的元素 Item。

关于您想要的查询，恕我直言，我认为在 Linq to Entities 中没有更有效的查询来获得您期望我上面提出的查询的结果。查看生成的 sql 代码：

   SELECT 
        [Filter1].[Id] AS [Id], 
        [Filter1].[Name] AS [Name]
   FROM   (SELECT [Extent1].[Id] AS [Id], [Extent1].[Name] AS [Name]
            FROM  [dbo].[Items] AS [Extent1]
            INNER JOIN [dbo].[ItemCategories] AS [Extent2] ON [Extent1].[Id] = [Extent2].[Item_Id]
            WHERE [Extent2].[Category_Id] IN (1, 2) ) AS [Filter1]
            INNER JOIN  (SELECT [Extent3].[Item_Id] AS [Item_Id]
            FROM  [dbo].[TagItems] AS [Extent3]
            INNER JOIN [dbo].[Tags] AS [Extent4] ON [Extent4].[Id] = [Extent3].[Tag_Id]
            WHERE ([Extent4].[Name] IN (N'Difficult', N'Technical')) AND ([Extent4].[Name] IS NOT NULL) ) AS [Filter2] ON [Filter1].[Id] = [Filter2].[Item_Id]
   WHERE [Filter1].[Name] LIKE @p__linq__0 ESCAPE N'~'

如您所见，它与您期望的查询非常相似。

Entity Framework 具有 2 个多对多连接的查询

Entity Framework query with 2 many-to-many joins

c#

sql-server

entity-framework

entity-framework-5