如何在C＃中的搜索表單中實現LIKE操作？

Question

我在下面的代碼中使用了我的搜索邏輯，基本上，它在相應的文本框或下拉列表中存在輸入時評估字段，我的問題是代碼僅用於完全匹配，最好的實現方式是什麼a .Contains（）搜索還是實現SQL LIKE搜索的搜索？

private void btnSearch_Click(object sender, EventArgs e) 
    {    
     bool ok_username = !txtUsername.IsBlank(); 
     bool ok_firstname = !txtFirstname.IsBlank(); 
     bool ok_lastname = !txtLastName.IsBlank(); 
     bool ok_userlevels = cboUserLevels.IsItemInList(); 

     _query = from _v 
       in Classes.Data.getdb().vUsers 
       where 
        _v.username ==(ok_username ? txtUsername.Text : _v.username) && 
        _v.firstname == (ok_firstname ? txtFirstname.Text : _v.firstname) && 
        _v.lastname == (ok_lastname ? txtLastName.Text : _v.lastname) && 
        _v.userlevel == (ok_userlevels ? cboUserLevels.Text : _v.userlevel) 
       select _v; 
     gv.DataSource = _query ; 


    } 

當我嘗試括在一。載（）函數中的eval表達，它說，僅可以在客戶端上被求值的表達式可以被用作在功能。載的參數。謝謝！感謝任何建議！

---

好吧，

感謝Alex給我關於SQLMethods功能的想法。但是現在我會跟着桑德的鏈式表達樹的建議。如果任何人都可以縮短代碼，我會非常感激，因爲在這個解決方案中，我有兩組查詢，一組是針對靈活性的，另一組是針對精確搜索。再次感謝Alex和Sander！

private void btnSearch_Click(object sender, EventArgs e) 
    {    

     bool ok_username = !txtUsername.IsBlank(); 
     bool ok_firstname = !txtFirstname.IsBlank(); 
     bool ok_lastname = !txtLastName.IsBlank(); 
     bool ok_userlevels = cboUserLevels.IsItemInList(); 

     if (optMode.CheckedIndex == 0) //flexible search, the else part is the exact search 
     { 
      _query = (from _v 
         in Classes.Data.getdb().vUsers 
         where 
         _v.userlevel == (ok_userlevels ? cboUserLevels.Text : _v.userlevel) 
         select _v); 

      if (ok_username) 
       _query = _query.Where(x => x.username.Contains(txtUsername.Text)); 

      if (ok_firstname) 
       _query = _query.Where(x => x.firstname.Contains(txtFirstname.Text)); 

      if (ok_lastname) 
       _query = _query.Where(x => x.lastname.Contains(txtLastName.Text)); 
     } 
     else 
     { 
      _query = (from _v 
         in Classes.Data.getdb().vUsers 
         where 
         _v.username == (ok_username ? txtUsername.Text : _v.username) && 
         _v.firstname == (ok_firstname ? txtFirstname.Text : _v.firstname) && 
         _v.lastname == (ok_lastname ? txtLastName.Text : _v.lastname) && 
         _v.userlevel == (ok_userlevels ? cboUserLevels.Text : _v.userlevel) 
         select _v); 
     } 

     gv.DataSource = _query.ToList(); 



    } 

Answer 1

您可以通過一步本查詢更具體的步驟：

var _query = from _v in Classes.Data.getdb().vUsers 
      select v; 

if(!txtUsername.IsBlank()) 
    _query = _query.Where(x => x.username.Contains(txtUsername.Text)); 

if(!txtFirstName.IsBlank()) 
    _query = _query.Where(x => x.firstname.Contains(txtFirstName.Text)); 

// etc. 

gv.DataSource = _query; 

Answer 2

你必須調用Contains從數據庫裏面的String：

_query = 
    from _v in Classes.Data.getdb().vUsers 
    where 
    (txtUsername.IsBlank() || _v.username.Contains(txtUsername.Text)) && 
    (txtFirstname.IsBlank() || _v.firstname.Contains(txtFirstname.Text)) && 
    (txtLastName.IsBlank() || _v.lastname.Contains(txtLastName.Text)) && 
    (!cboUserLevels.IsItemInList() || _v.userlevel.Contains(cboUserLevels.Text)) 
    select _v; 

如果你想使用SQL Like運算符，可以使用System.Linq.Data.SqlClient.SqlMethods：

_query = 
    from _v in Classes.Data.getdb().vUsers 
    where 
    SqlMethods.Like(_v.username, "%" + txtUsername.Text + "%") && 
    SqlMethods.Like(_v.firstname, "%" + txtFirstname.Text + "%") && 
    SqlMethods.Like(_v.lastname, "%" + txtLastName.Text + "%") && 
    SqlMethods.Like(_v.userlevel, "%" + cboUserLevels.Text + "%") 
    select _v;