回传同时循环
回传同时循环
提问于 2018-12-06 16:45:10
我在c#中有一个带有数据库的方法。现在我尝试返回值，但是因为字符串是在while循环中创建的，所以它说它不存在。是否有一种方法可以返回字符串kampioen及其在with read循环中创建的值？
public string getkampioen(string selecteditem)
{
using (MySqlConnection connection = new MySqlConnection(connectionString))
{
connection.Open();
string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader Reader = cmd.ExecuteReader();
while (Reader.Read())
{
string kampioen = (string)Reader["aantalkampioenschappen"].ToString();
}
return kampioen;
}
}回答 3
Stack Overflow用户
回答已采纳
发布于 2018-12-06 16:48:01
可以在while循环之前声明字符串。
public string getkampioen(string selecteditem)
{
using (MySqlConnection connection = new MySqlConnection(connectionString))
{
connection.Open();
string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader Reader = cmd.ExecuteReader();
string kampioen = "";
while (Reader.Read())
{
kampioen = (string)Reader["aantalkampioenschappen"].ToString();
}
return kampioen;
}
}Stack Overflow用户
发布于 2018-12-06 16:47:34
只需将声明移出循环：
public string getkampioen(string selecteditem)
{
string kampioen; //declare here
using (MySqlConnection connection = new MySqlConnection(connectionString))
{
connection.Open();
string query = ("select * FROM clubs where naam = '" + selecteditem + "'");
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader Reader = cmd.ExecuteReader();
while (Reader.Read())
{
kampioen = (string)Reader["aantalkampioenschappen"].ToString();
}
return kampioen;
}
}Stack Overflow用户
发布于 2018-12-06 16:52:27
正如其他人所说，将kampioen移出循环。但是，如果希望获得特定值而不是随机值(如果返回多个记录)，则可能希望将字符串连接起来或将结果限制在第一行，如下所示：
public string getkampioen(string selecteditem)
{
string kampioen = string.empty; // declared outside of the while
using (MySqlConnection connection = new MySqlConnection(connectionString))
{
connection.Open();
string query = ("select * FROM clubs where naam = '" + selecteditem + "' limit one");
MySqlCommand cmd = new MySqlCommand(query, connection);
MySqlDataReader Reader = cmd.ExecuteReader();
while (Reader.Read())
{
kampioen = (string)Reader["aantalkampioenschappen"].ToString();
}
return kampioen;
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/53656025
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