使用 C# 更新 mySQL 表
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update a mySQL table using C#
提问by user498213
I have written some C# to update a MySql table but I get an exception every time I call the method ExecuteNonQuery(). I have researched this on the web and every solution I find produces the same error. I have an open connection to the database and the update query to the database is written correctly. The code that I have so far come up with is :
我编写了一些 C# 来更新 MySql 表，但每次调用方法 ExecuteNonQuery() 时都会出现异常。我在网上对此进行了研究，我找到的每个解决方案都会产生相同的错误。我有一个与数据库的开放连接，并且对数据库的更新查询已正确写入。到目前为止，我想出的代码是：
public int executeUpdate()
{
int result = 0;
if (isConnected)
{
try
{
MySqlConnection cn = new MySqlConnection(connection.ConnectionString);
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = cn;
cmd.CommandText = "UPDATE test SET status_id = 1 WHERE test_id = 1";
int numRowsUpdated = cmd.ExecuteNonQuery();
}
catch (MySqlException exSql)
{
Console.Error.WriteLine("Error - SafeMySql: SQL Exception: " + query);
Console.Error.WriteLine(exSql.StackTrace);
}
catch (Exception ex)
{
Console.Error.WriteLine("Error - SafeMySql: Exception: " + query);
Console.Error.WriteLine(ex.StackTrace);
}
}
else
Console.Error.WriteLine("Error - SafeMySql: executeQuery failed. Not connected to DB");
}
回答by DOK
I don't see the connection being opened.
我没有看到正在打开的连接。
Here is an example from MSDN: even inside a using block, they open the connection explicitly
这是MSDN 中的一个示例：即使在 using 块中，它们也会显式打开连接
private static void CreateCommand(string queryString,
string connectionString)
{
using (SqlConnection connection = new SqlConnection(
connectionString))
{
SqlCommand command = new SqlCommand(queryString, connection);
command.Connection.Open();
command.ExecuteNonQuery();
}
}
Edit: The principle is the same for MySQLas it is for SQL Server:
编辑：MySQL的原理与SQL Server的原理相同：
public void CreateMySqlCommand(string myExecuteQuery, MySqlConnection myConnection)
{
MySqlCommand myCommand = new MySqlCommand(myExecuteQuery, myConnection);
myCommand.Connection.Open();
myCommand.ExecuteNonQuery();
myConnection.Close();
}
回答by Espen Burud
Change your try section to the code below:
将您的尝试部分更改为以下代码：
try
{
using(MySqlConnection cn = new MySqlConnection(connection.ConnectionString))
{
MySqlCommand cmd = new MySqlCommand();
cmd.Connection = cn;
cmd.CommandText = "UPDATE test SET status_id = 1 WHERE test_id = 1";
cn.Open();
int numRowsUpdated = cmd.ExecuteNonQuery();
cmd.Dispose();
}
}
The connection must be opened before you execute a command. In the example above the command object will immediately be disposed and the connection object will implcitly be closed and disposed when you leave the using section.
在执行命令之前必须打开连接。在上面的示例中，当您离开 using 部分时，命令对象将立即被释放，而连接对象将被隐式关闭和释放。
