LINQ 了解非等值联接

发布于 2024-10-21 03:15:49 字数 1125 浏览 2 评论 0原文

我使用 asp.net 4、ef 4 和 c#、LINQ 和非等值连接。

下面我写了两个非等值连接的例子。两者在我的模型中都运行良好。

因为我对 Linq 还很陌生，所以我想问您：

您建议我在代码中采用哪种语法类型？
哪个代码性能更快？

感谢您的帮助：

这里有一些有用的链接：

http://msdn.microsoft.com /en-us/library/bb882533.aspx

http://msdn .microsoft.com/en-us/library/bb311040.aspx

http ://msdn.microsoft.com/en-us/library/bb310804.aspx

// Query sintax
var queryContents = 
    from cnt in context.CmsContents
    let cntA =
        from a in context.CmsContentsAssignedToes
        select a.CmsContent.ContentId
    where cntA.Contains(cnt.ContentId) == false
    select cnt;

// Query method   
var queryContents02 =
    from c in context.CmsContents
    where !(
        from a in context.CmsContentsAssignedToes 
        select a.ContentId).Contains(c.ContentId)
    select c;

原文

I use asp.net 4, ef 4 and c#, LINQ and Non-Equijoins.

Here below I wrote two examples of Non-Equijoins.
Both are working fine in my model.

Because I'm pretty new to Linq, I would like ask you:

Which syntax typology would you advice me to adopt in my code?
Which code performance faster?

Thanks for your help:

Here some useful links:

http://msdn.microsoft.com/en-us/library/bb882533.aspx

http://msdn.microsoft.com/en-us/library/bb311040.aspx

http://msdn.microsoft.com/en-us/library/bb310804.aspx

// Query sintax
var queryContents = 
    from cnt in context.CmsContents
    let cntA =
        from a in context.CmsContentsAssignedToes
        select a.CmsContent.ContentId
    where cntA.Contains(cnt.ContentId) == false
    select cnt;

// Query method   
var queryContents02 =
    from c in context.CmsContents
    where !(
        from a in context.CmsContentsAssignedToes 
        select a.ContentId).Contains(c.ContentId)
    select c;

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∝单色的世界 2024-10-28 03:15:49

我会提示第三个选项：

var validContentIds = from a in context.CmsContentsAssignedToes 
                      select a.ContentId;

var queryContents = from cnt in context.CmsContents
                    where !validContentIds.Contains(cnt.ContentId)
                    select cnt;

或者（等效地）：

var validIds = context.CmsContentsAssignedToes.Select(a => a.ContentId);

var queryContents = context.CmsContents
                           .Where(cnt => !validIds.Contains(cnt.ContentId));

我不希望性能受到影响 - 我希望所有这些最终都会得到相同的 SQL。

I'd prompt for a third option:

var validContentIds = from a in context.CmsContentsAssignedToes 
                      select a.ContentId;

var queryContents = from cnt in context.CmsContents
                    where !validContentIds.Contains(cnt.ContentId)
                    select cnt;

Or alternatively (and equivalently):

var validIds = context.CmsContentsAssignedToes.Select(a => a.ContentId);

var queryContents = context.CmsContents
                           .Where(cnt => !validIds.Contains(cnt.ContentId));

I wouldn't expect the performance to be impacted - I'd expect all of these to end up with the same SQL.

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