Question

如何将以下产生正确结果的T-SQL查询转换为C＃中的LINQ表达式？

WITH    CTE
          AS ( SELECT RN = ROW_NUMBER() OVER ( PARTITION BY dbo.Product.ID ORDER BY dbo.Picture.UpdatedDate ASC )
                   ,Product.ID
                   ,Product.Name
                   ,Picture.Path
                FROM Dbo.Product
                INNER JOIN dbo.Product_Picture_Mapping
                    ON dbo.Product_Picture_Mapping.ProductID = dbo.Product.ID
                INNER JOIN dbo.Picture
                    ON dbo.Picture.ID = dbo.Product_Picture_Mapping.PictureID)
    SELECT ID AS 'ID'
           ,Name AS 'Name'
        FROM CTE
        WHERE RN = 1

我尝试过以下代码。

var result= (from c in cd.Product
              join pp in cd.Product_Picture_Mapping
                            on c.ID equals pp.ProductID
                        join pcc in cd.Picture
                            on pp.PictureID equals pcc.ID
                        select new ProductViewModel() { PicturePath = pcc.Path, ProductName = c.Name, ProductID = c.ID}).ToList();

Answer 1

查看以下内容是否有效：

var result= (from c in cd.Product
              join pp in cd.Product_Picture_Mapping
                            on c.ID equals pp.ProductID
              let pcc = pp.Pictures.FirstOrDefault()
              select new ProductViewModel() 
              {
                  PicturePath = pcc.Path,
                  ProductName = c.Name,
                  ProductID = c.ID
              }).ToList();

查看您的表名，看起来您有一个多表（product_picture_mapping），EF可以优化，让您可以选择执行以下操作：

var result = from c in cd.Product
             let ppc = c.Pictures.FirstOrDefault()
             select new ProductViewModel 
             {
                 PicturePath = pcc.Path, 
                 ProductName = c.Name, 
                 ProductID = c.ID
             };

如何将T-SQL转换为LINQ？

1 个答案: