SQL Server查詢不返回任何結果在asp.net

Question

我想通過在刑事數據庫中查找他的NIC號碼來檢查一個人是否有過去的犯罪歷史。但是查詢不會獲取任何數據，儘管數據庫中沒有異常和相關數據，但數據讀取器仍爲空。

請參見下面的代碼：

SqlCommand cmd5 = new SqlCommand("select * from criminal where NIC ="+nic, conn); 
string nic = "null"; 

foreach (var person in allInvolved) 
{ 
    conn.Open(); 
    nic = person.NIC; 

    dr3 = cmd5.ExecuteReader(); 

    if (dr3.HasRows) 
    { do something } 
    else if (!dr3.HasRows) 
    { do something else} 
} 

變量NIC中有正確的值，我檢查它在調試。我不知道我哪裏錯了。如果您需要關於代碼的其他信息，請詢問。

在此先感謝。

Answer 1

當你這樣做：

SqlCommand cmd5 = new SqlCommand("select * from criminal where NIC ="+nic, conn); 

的nic當前值在那一刻使用;這不要緊，你改變什麼nic到事後：

nic = person.NIC; 
dr3 = cmd5.ExecuteReader(); 

因爲該值不使用。理想情況下，你應該參數：

SqlCommand cmd5 = new SqlCommand(
    "select * from criminal where NIC = @nic", conn); 
var param = cmd5.Paramters.Add("nic", SqlDbType.SomethingRelevant); 
// ^^^ note: I don't know what the data type is, you'll need to pick that 

foreach(...) { 
    param.Value = ((object)person.NIC) ?? DBNull.Value; 
    using(var dr3 = cmd5.ExecuteReader()) { 
     // ... 
    } 
} 
... 

另外還要注意，很多這些對象都是IDisposable並應在using塊;或者，看看像「小巧玲瓏」的工具，所以你可以做這樣的事情：

var criminals = conn.Query<Criminal>(
    "select * from criminal where NIC = @nic", 
    new { nic = person.NIC}).AsList(); 

Answer 2

嘗試此

SqlConnection con = new SqlConnection(connectionString); 
SqlCommand cmd = new SqlCommand(); 
cmd.Connection = con; 
con.Open(); 

foreach (var person in allInvolved) 
{ 
nic = person.NIC; 
cmd.CommandText = "select * from criminal where NIC ="+nic; 
dr3 = cmd.ExecuteReader(); 

while (dr3.Read()) 
{ 
     if (dr3.HasRows) 
     { do something} 
     else if (!dr3.HasRows) 
     { do something else} 
} 

} con.Close（）;