加入3表

本文介绍了加入3表的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我想通过LINQ加入3表，我这样做了： var results = northwind.Products.Join（northwind.Categories，c => c.CategoryID，d => d.CategoryID ，（c，d）=> new {c.ProductID，c.ProductName，c.SupplierID，d.CategoryName}） .Where（q => q.ProductID> 12）。 （northwind.Suppliers，f => f.SupplierID，g => g.SupplierID，（f，g） => new {f.CategoryName，f.ProductName，g.CompanyName，g.ContactName， g.Country}）; 但查询太长了，谁能告诉我写得更短？ 谢谢。

解决方案

这是一种不同的编写方式，它更简洁，但最终两种方式在后端产生相同的SQL。

SELECT [t2]。[CategoryName]，[t0]。[ProductName]，[t1]。[CompanyName]，[t1 ]。[ContactName]，[t1]。[Country]

FROM [dbo]。[Products] AS [t0]

INNER JOIN [dbo]。[供应商] AS [t1] ON [t0]。[SupplierID] =（[t1]。[SupplierID]）

INNER JOIN [dbo]。[Categories] AS [t2] ON [t0]。[CategoryID] =（[t2]。[CategoryID]）

WHERE [t0]。[ProductID]> 12 var qresult = from p in db .Products

其中 p.ProductID> ; 12

join s in db.Suppliers on p.SupplierID equals s.SupplierID

join c in db.Categories on p.CategoryID equals c.CategoryID

选择 new {c.CategoryName，p.ProductName，s.CompanyName，s.ContactName，s.Country};

I want to join 3 table by LINQ , i did this : var results = northwind.Products.Join(northwind.Categories, c => c.CategoryID, d => d.CategoryID, (c, d) => new { c.ProductID, c.ProductName, c.SupplierID, d.CategoryName })                                            .Where(q => q.ProductID > 12)                                            .Join(northwind.Suppliers, f => f.SupplierID, g => g.SupplierID, (f, g) => new { f.CategoryName, f.ProductName, g.CompanyName, g.ContactName, g.Country });but the query is too long, who can tell me to write it shorter ?thank.         

解决方案

This is a different way to write it which is a little cleaner, but in the end both ways produce the same exact SQL on the back end.

SELECT [t2].[CategoryName], [t0].[ProductName], [t1].[CompanyName], [t1].[ContactName], [t1].[Country]

FROM [dbo].[Products] AS [t0]

INNER JOIN [dbo].[Suppliers] AS [t1] ON [t0].[SupplierID] = ([t1].[SupplierID])

INNER JOIN [dbo].[Categories] AS [t2] ON [t0].[CategoryID] = ([t2].[CategoryID])

WHERE [t0].[ProductID] > 12var qresult = from p in db.Products

where p.ProductID > 12

join s in db.Suppliers on p.SupplierID equals s.SupplierID

join c in db.Categories on p.CategoryID equals c.CategoryID

select new {c.CategoryName, p.ProductName, s.CompanyName, s.ContactName, s.Country };