c# - 加入 Linq 的最佳方式

Question

我一直在使用下面的第一种方法，但后来我找到了第二种方法，想知道它们之间的区别以及哪种方法最好。

有什么区别:

from a in this.dataContext.reglements
join b in this.dataContext.Clients on a.Id_client equals b.Id 
select...

和

from a in this.dataContext.reglements
from b in this.dataContext.Clients
where a.Id_client == b.Id 
select...

Answer 1

我创建了一个测试用例来测试差异，在您的场景中，结果证明它们是相同的。

我的测试示例使用 AdventureWorks 但基本上之间存在关联

Products->CategoryId->Categories

var q = (
    from p in Products
    from c in Categories
        where p.CategoryID==c.CategoryID
    select p
);

q.ToList();

生成此 SQL:

SELECT [t0].[ProductID], [t0].[ProductName], [t0].[CategoryID]
    FROM [Products] AS [t0], [Categories] AS [t1]
WHERE [t0].[CategoryID] = ([t1].[CategoryID])

---

var q2 = (
    from p in Products 
    join c in Categories 
        on p.CategoryID equals c.CategoryID
    select p);

q2.ToList();

生成此 sql:

SELECT [t0].[ProductID], [t0].[ProductName], [t0].[CategoryID]
FROM [Products] AS [t0]
INNER JOIN [Categories] AS [t1] ON [t0].[CategoryID] = ([t1].[CategoryID])