使用LINQ构建动态查询
问题描述:
我将rebuilding this website php/mysql导入到asp.net中。我正在构建页面标题中的主卡搜索表单。有一个文本输入,多个下拉列表(全部指向不同的列)和一些条件搜索选项。使用LINQ构建动态查询
对于mysql版本,我能够使用条件来构建包含查询的sting,然后执行它。
//MySql/PHP example
$query = "SELECT * FROM cards WHERE ";
//Encounter_set
if (isset($_GET['Encounter_Set']){
$query.= "Encounter_Set=:Encounter_Set AND ";
$queryArray['Encounter_Set'] = $_GET['Encounter_Set'];
}
//radio statements
switch ($_GET['radio']) {
case "All": $query.= "(Title LIKE :terms OR Traits LIKE :terms OR Shadow_Text LIKE :terms OR Text LIKE :terms)";break;
case "Title": $query.= "(Title LIKE :terms)";break;
case "Traits": $query.= "(Traits LIKE :terms)";break;
case "Text": $query.= "(Shadow_Text LIKE :terms OR Text LIKE :terms)"; break;
default: $query.= "(Title LIKE :terms OR Traits LIKE :terms OR Shadow_Text LIKE :terms OR Text LIKE :terms)";
}
//Finally
$result = $db_con->prepare($query);
我该怎么去做这件事在LINQ?
答
using (var context = new MyDbContext())
{
IQueryable<Card> query = context.Cards;
if (!string.IsNullOrEmpty(Encounter_Set))
{
query = query.Where(c => c.Encounter_Set == Encounter_Set);
}
switch (radio)
{
default:
case "All":
query = query.Where(c => c.Title.Contains(terms)
|| c.Traits.Contains(terms)
|| c.Shadow_Text.Contains(terms)
|| c.Text.Contains(terms));
break;
case "Title":
query = query.Where(c => c.Title.Contains(terms));
break;
case "Traits":
query = query.Where(c => c.Traits.Contains(terms));
break;
case "Text":
query = query.Where(c => c.Shadow_Text.Contains(terms)
|| c.Text.Contains(terms));
break;
}
// ...
return query.ToList(); // Execute the query
}
LINQ允许您撰写查询。 http://*.com/questions/11194/conditional-linq-queries –
不会这inital声明:'var logs =从登录上下文.Logs选择日志;'将得到所有行表?从表中拉出每一行开始似乎效率不高。 – Mason240
不,linq是懒惰的,它不会执行查询,直到您实际尝试枚举值 –