Question

我不知道我的错误在哪里..我已经把connection.close（）放到了各处。我正在使用microsoft visual studio 2013 C＃中的访问数据库。它在没有数据库的情况下运行良好，但是当我尝试向其中添加数据库时，问题就开始发生了。

private void btnLogin_Click(object sender, EventArgs e)
    {
        connection.Open();
        OleDbCommand command = new OleDbCommand();
        command.Connection = connection;
        command.CommandText = "SELECT * from Login where [Username]='" + txtUser.Text + "' and [Password]='" + txtPass.Text + "' ";
        OleDbDataReader reader = command.ExecuteReader();
        int count = 0;
        while (reader.Read())
        { 
            count = count + 1;
        }
        if (count == 1)
        {
            connection.Open();
            Form main = new AdminMain();
            main.Show();
            this.Hide();

            try
            {
                connection.Open();
                command.Connection = connection;
                command.CommandText = "INSERT into LogHisto ([Username],[LogDate],[LogTime]) values ('" + txtUser.Text + "','" + dateTimePicker1.Text + "','" + dateTimePicker2.Text + "')";
                command.ExecuteNonQuery();
                connection.Close();
            }

            catch (Exception ex)
            {
                MessageBox.Show("Error" + ex);
            }
            connection.Close();
        }

        else
        {
            MessageBox.Show("Username/Password is incorrect");
            try
            {
                connection.Open();
                command.Connection = connection;
                command.CommandText = "INSERT into LogHisto (Username,LogDate,LogTime) values ('" + txtUser.Text + "','" + dateTimePicker1.Text + "','" + dateTimePicker2.Text + "')";
                command.ExecuteNonQuery();
                connection.Close();
            }

            catch (Exception ex)
            {
                MessageBox.Show("Error" + ex);
            }
        }
        connection.Close();
    }

Answer 1

    if (count == 1)
    {
        connection.Open(); // <-------------FIRST TIME
        Form main = new AdminMain();
        main.Show();
        this.Hide();

        try
        {
            connection.Open();// <-------------SECOND TIME
            command.Connection = connection;
            command.CommandText = "INSERT into LogHisto ([Username],[LogDate],[LogTime]) values ('" + txtUser.Text + "','" + dateTimePicker1.Text + "','" + dateTimePicker2.Text + "')";
            command.ExecuteNonQuery();
            connection.Close();
        }

        catch (Exception ex)
        {
            MessageBox.Show("Error" + ex);
        }
        connection.Close();
    }

在此代码块中，您打开两次相同的连接，因为您有此异常。只需删除connection.Open()之一;您还需要删除其中一个connection.Close();。

此外，您应该在查询中使用参数！这将阻止sql注入。我建议你为DataAccess制作不同的课程。这样可以防止这样的错误。

错误：连接未关闭，连接的当前状态已打开

1 个答案: