如何使用sqCommand.ExecuteReader（）返回数据;？

Question

我有sqlite的方法，使SELECT查询：

try { 
myConn.Open(); 

using(SQLiteCommand sqCommand = new SQLiteCommand(sql, myConn)) { 
    sqCommand.CommandText = sql; 
    SQLiteDataReader reader = sqCommand.ExecuteReader(); 
    return reader.GetString(0); 
} 
} catch (Exception e) { 
// do exception handling 
} 

我试图让最后插入的ID：

sql = 'SELECT id FROM Pacients ORDER BY id DESC LIMIT 1'; 

我试图迪，像：

return reader.GetString(0); 

它抛出我打破例外“没有当前行”

Answer 1

Afte r调用ExecuteReader需要调用Read以定位数据集的第一条记录。 Read返回true/false以通知您是否有要读取的记录。所以，你的代码更改为

try { 
myConn.Open(); 

using(SQLiteCommand sqCommand = new SQLiteCommand(sql, myConn)) { 
    sqCommand.CommandText = sql; 
    SQLiteDataReader reader = sqCommand.ExecuteReader(); 
    if(reader.Read()) 
    return reader.GetString(0); 
    else 
    return ""; // or whatever you want to return if no records are present 
} 
} catch (Exception e) { 
// do exception handling 
} 

说，记住，如果你想要一个像你在查询必须从单行检索只是一列，然后它是更好，而不是使用的ExecuteReader

try { 
myConn.Open(); 

using(SQLiteCommand sqCommand = new SQLiteCommand(sql, myConn)) { 
    sqCommand.CommandText = sql; 
    object result = sqCommand.ExecuteScalar(); 
    return result != null ? result.ToString() : ""; 
} 
} catch (Exception e) { 
// do exception handling 
} 

的ExecuteScalar