MySQL连接抛出null引用 [英] MySQL connection throws null reference

问题描述

我的MySQL连接抛出null引用，尽管这个代码在一年前运行良好。

调试器指示异常的行包含

connection = new MySqlConnection（connectionString）; ：

My MySQL connection throws null reference although this code worked well one year ago.
The line where the debugger indicates the exception contains
"connection = new MySqlConnection(connectionString);":

DBConnect MySqlConnection = new DBConnect();

string[] resultArray = MySqlConnection.GetValidUser(
    "tbl_user",
    tbEmail.Text, 
    tbPassword.Text
);

//THROWS null reference exception in method 'private bool OpenConnection()'
//A first chance exception of type 'System.ArgumentException' occurred in System.Data.dll

这是我的DBConnect类：

This is my DBConnect class:

class DBConnect
{
    private MySqlConnection connection;
    private string server;
    private string database;
    private string uid;
    private string password;

    public DBConnect()
    {
        server = "x.x.x.x";
        database = "...";
        uid = "...";
        password = "...";

        string connectionString = "SERVER=" + server + ";" +
                                  "DATABASE=" + database + ";" +
                                  "UID=" + uid + ";" +
                                  "PASSWORD=" + password + ";";

        connection = new MySqlConnection(connectionString);
    }

    private bool OpenConnection()
    {
        try
        {
            connection.Open();
            return true;
        }
        catch (MySqlException ex)
        {
            switch (ex.Number)
            {
                case 0:
                    MessageBox.Show("Cannot connect to MySQL server.");
                    break;

                case 1045:
                    MessageBox.Show("Invalid username or password.");
                    break;
            }
            return false;
        }
    }

    public string[] GetValidUser(string dbTable, string dbUsername, string dbPassword)
    {
        string query = "SELECT id,email,password FROM " + dbTable +
                       " WHERE email='" + dbUsername +
                       "' AND password='" + dbPassword + "'";

        string[] resultArray = new string[3];

        if (this.OpenConnection() == true)
        {
            MySqlCommand cmd = new MySqlCommand(query, connection);
            MySqlDataReader dataReader = cmd.ExecuteReader();

            while (dataReader.Read())
            {
                resultArray[0] = dataReader.GetInt32(0).ToString();
                resultArray[1] = dataReader.GetString(1);
                resultArray[2] = dataReader.GetString(2);
            }

            dataReader.Close();
            this.CloseConnection();
        }
        return resultArray;
    }
}

可以找到数据库类的原始代码< a href =http://www.codeproject.com/Articles/43438/Connect-C-to-MySQL =nofollow>此处。

The original code for the database class can be found here.

推荐答案

其他事情，它听起来像你有连接字符串的问题 - 从注释：

Among other things, it sounds like you have problems with the connection string - from comments:

而connection = new MySqlConnection（）; connection.ConnectionString = connectionString;抛出一个异常语句connection = new MySqlConnection（）;不... ...

While "connection = new MySqlConnection(); connection.ConnectionString = connectionString;" throws an exception the statement "connection = new MySqlConnection();" does not...

这里的区别是：在后面的 em> - 所以它听起来像你的连接字符串不能正确转义的值（最有可能的密码）;你可以尝试：

The difference here is simply: in the latter you aren't setting the connection string - so it sounds like your connection string is not correctly escaping the values (most likely, the password); you could try:

var cs = new DbConnectionStringBuilder();
cs["SERVER"] = server;
cs["DATABASE"] = database;
cs["UID"] = uid;
cs["PASSWORD"] = password;
var connectionString = cs.ConnectionString;

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