构建一个定制|在LINQ查询进步？ [英] Building a custom|progressive query in LINQ?

问题描述

我有五个文本框的页面时，每一个重$ P $在我的数据库表和一个搜索按钮psenting字段：

如果我是使用SQL我可以建立我的SQL语句，这取决于域在他们的数据。

不过，我想使用LINQ和我在一个不知如何做到这一点。例如，看看下面的查询：

 变种DB =新BookDBDataContext（）;        变种Q =
            从在db.Books
            其中，a.Title.Contains（txtBookTitle）及＆放大器;
                  a.Author.Contains（txtAuthor）及＆放大器;
                  a.Publisher.Contains（txtPublisher）
            选择a.ID;
 

上面的查询将返回，所有的字段匹配表数据。但是，如果用户没有输入什么在txtAuthor领域的作者？如果我建立这个作为查询字符串，我可以检查每个字段的数据，并将其添加到查询字符串。由于这是LINQ，我不能动态地改变搜索条件，它似乎。

任何意见将是极大的AP preciate！

解决方案

 变种DB =新BookDBDataContext（）; 在db.Books变种Q =（从
          其中，a.Title.Contains（txtBookTitle））; 如果（！String.IsNullOrEmpty（txtAuthor））
 {
      Q = q.Where（一个= GT; a.Author.Contains（txtAuthor））;
 }
 如果（！String.IsNullOrEmpty（txtAuthor））
 {
      Q = q.Where（一个= GT; a.Publisher.Contains（txtPublisher））;
 } 变种的id = q.Select（一个= GT; a.ID）;
 

I have a page with five text boxes, each one representing a field in my database table and a search button:

If I were using SQL I could build my SQL statement depending on which fields have data in them.

However, I want to use LINQ, and I'm at a loss as to how to accomplish this. For instance, take a look at the query below:

        var db = new BookDBDataContext();

        var q =
            from a in db.Books
            where a.Title.Contains(txtBookTitle) &&
                  a.Author.Contains(txtAuthor) &&
                  a.Publisher.Contains(txtPublisher)
            select a.ID;

The query above will return data where all the fields match data in the table. But, what if the user didn't enter an Author in the txtAuthor field? If I were building this as a query string, I could check each field for data and add it to the query string. Since this is LINQ, I can't dynamically change the search criteria, it seems.

Any advice would be greatly appreciate!

解决方案

 var db = new BookDBDataContext();

 var q = (from a in db.Books
          where a.Title.Contains(txtBookTitle));

 if(!String.IsNullOrEmpty(txtAuthor)) 
 {
      q = q.Where(a => a.Author.Contains(txtAuthor));
 }


 if(!String.IsNullOrEmpty(txtAuthor)) 
 {
      q = q.Where(a => a.Publisher.Contains(txtPublisher));
 }

 var id = q.Select(a => a.ID);

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