使用LINQ构建动态查询

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？

来源

2012-12-15 Mason240

LINQ允许您撰写查询。 http://stackoverflow.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 –

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 
}

来源

2012-12-15 17:27:13

使用LINQ构建动态查询

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