LINQ：如何构建动态查询？ [英] LINQ: How to build dynamic query?

问题描述

您好，

与逆戟鲸玩了一点，并通过构建动态

查询来解决问题。我想构建一个动态的where子句，但只有参数

不为空=（TextBox.Text！=""）。

通过构建一个字符串很简单，但如何用LINQ做呢？


string sql ="" ;;

if（TextBox1.Text！=" "）

sql + =" Columns_1 =''" + TextBox1.Text +"''" ;;

if（TextBox2.Text！=" ;"）

sql + =" Columns_2 =''" + TextBox2.Text +"''" ;;

如何将if查询包括在内linq ???


var query =来自db.MyTable中的c

其中c.Column_1 == TextBox1.Text&&

c.Column_2 == TextBox2.Text

选择c;


谢谢！


-Stefan

Hello,
played a little with orcas and went into a problem by building dynamic
queries. I want to build a dynamic where clause but only with parameters that
are not empty =(TextBox.Text != "").
Doing this by building a string is very simple, but how to do it with LINQ?

string sql = "";
if (TextBox1.Text != "")
sql += "Columns_1=''"+TextBox1.Text+"''";
if (TextBox2.Text != "")
sql += "Columns_2=''"+TextBox2.Text+"''";
How to include the if query to linq???

var query = from c in db.MyTable
where c.Column_1 == TextBox1.Text &&
c.Column_2 == TextBox2.Text
select c;

Thank you!

-Stefan

推荐答案

（稍微简单）：


if（！string.IsNullOrEmpty（inputA）） {

query = query.Where（x = x.PropertyB == inputA）;

}

i f（！string.IsNullOrEmpty（inputB））{

query = query.Where（x = x.PropertyB == inputB）;

}


Marc

(slightly simpler):

if (!string.IsNullOrEmpty(inputA)) {
query = query.Where(x =x.PropertyB == inputA);
}
if (!string.IsNullOrEmpty(inputB)) {
query = query.Where(x =x.PropertyB == inputB);
}

Marc

[注意拼写错误 - 应该是PropertyA]

[watch for typo - should have been PropertyA]

它'' s实际上比忽略查询稍微容易一点

It''s actually slightly easier than that if you ignore the query

表达式语法：

...

查询在许多情况下，表达式语法很好，但只需添加一个

" where"我更喜欢使用直接方法调用。

expression syntax:
...
Query expression syntax is nice in many cases, but just to add a
"where" clause I prefer to use the direct method call.

是的 - 我在我的初始帖子后发布了这个帖子（尽管有一个

错字）...我同意。

Yes - I posted that right after my initial post (albeit with a
typo)... I agree.

如果有必要，您甚至可以编写一个方法来抽象出来。

You could even write a method to abstract it out if necessary.

注意扩展这个？我能想出几种解释这个问题的方法，但我只是对你的意思感兴趣......？


Marc

Care to expand on this? I can think of a few ways of interpreting
this, but I''m just interested in how you mean it...?

Marc

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