一個參數例外

Question

當我通過給用戶名和密碼登錄，我得到一個異常：

「參數化查詢「（@username爲nvarchar（4000），@ password12 爲nvarchar（4000））SELECT我'期待 參數'@username'，它沒有提供。「

通過代碼：

public DataSet showoption1(seter set) 
{   
    string sql = "SELECT menue.menuename,roleid, [right].rightname,   
    role.rolename, employee.employeename, employee.password FROM [right] INNER JOIN 
    permission ON [right].rightid = permission.rightid INNER JOIN role ON 
    permission.roleid = role.roleid INNER JOIN emp_men INNER JOIN employee ON 
    emp_men.employeeid = employee.employeeid ON role.roleid = employee.roleid 
    INNER JOIN menue ON emp_men.menueid = menue.menueid 
    where employee.employeenamee=@username 
    AND employee.password=@password12"; 

    SqlCommand cmd = new SqlCommand(sql, con); 
    cmd.Parameters.AddWithValue("@username",set.Username); 
    cmd.Parameters.AddWithValue("@password12",set.Password); 
    SqlDataAdapter adptr = new SqlDataAdapter(cmd); 

    DataSet ds = new DataSet(); 
    adptr.Fill(ds); 
    int id= Convert.ToInt32(ds.Tables[2].Rows[0]["rooleid"]); 

    st.Username= Convert.ToString(ds.Tables[2].Rows[id]["roolename"]); 

    adptr.Dispose(); 

    return ds; 

    } 

Answer 1

由於DB的參數是如何工作的一個怪胎，如果set.Username是null會發生。因此：檢查set.Username是否爲null，並且可能在此情況下引發異常（因爲null用戶名聽起來像是一個錯誤）。

if(string.IsNullOrWhiteSpace(set.Username)) 
    throw new InvalidOperationException("No username was provided"); 

在更一般的情況，如果你做想傳遞null，你必須使用DBNull.Value代替，即是這樣的：

object username = set.Username; 
if(username == null) username = DBNull.Value; 
cmd.Parameters.AddWithValue("@username", username); 

Answer 2

你有兩個內部連接回不背相應的ON ...是導致解析錯誤？

SELECT 
     menue.menuename, 
     roleid, 
     [right].rightname, 
     role.rolename, 
     employee.employeename, 
     employee.password 
    FROM 
     [right] 
     INNER JOIN permission 
      ON [right].rightid = permission.rightid 
      INNER JOIN role 
       ON permission.roleid = role.roleid 
       INNER JOIN employee 
        ON role.roleid = employee.roleid 
        INNER JOIN emp_men 
        ON emp_men.employeeid = employee.employeeid 
        INNER JOIN menue 
         ON emp_men.menueid = menue.menueid 
    where 
      employee.employeenamee = @username 
     AND employee.password=@password12"; 

Answer 3

我認爲最可能的解釋是，set.Username爲空。

使用調試器逐個檢查並檢查值。