1

我想排除特定数据库的显示，但我排除的项目在运行程序时仍然显示。没有编译错误。

    private ComboBox cb;
    private Label label;
    private object[] databases;

    public MForm() {

       string connectionString =
          "Server=localhost;" +
          "Database=information_schema;" +
          "User ID=root;" +
          "Password=root;" +
          "Pooling=false";
       IDbConnection dbcon;
       dbcon = new MySqlConnection(connectionString);
       dbcon.Open();
       IDbCommand dbcmd = dbcon.CreateCommand();

        string sql = "SELECT COUNT(*) as count FROM information_schema.SCHEMATA"; //count the databases(string) and names it count
        dbcmd.CommandText = sql;                        //sends the string to sql
        IDataReader reader = dbcmd.ExecuteReader();     //assign the function to reader
        reader.Read();                                  //uses its getter(Read)
        int count = Convert.ToInt32(reader["count"]);   //converts the "count"(column) to integer

        reader.Close();
        reader = null;
        dbcmd.Dispose();
        dbcmd = null;

        databases = new object[count];

        dbcmd = dbcon.CreateCommand();
        sql = "show databases";
        dbcmd.CommandText = sql;
        reader = dbcmd.ExecuteReader();

        int i = 0;
        while(reader.Read()) {
            if((string) databases[i] != "information_schema" &&(string)databases[i] != "sakila" && (string)databases[i] != "enrollmentsystem" && (string)databases[i] != "mysql" &&
            (string)databases[i] != "world" && (string)databases[i] != "performance_schema"){
            databases[i] = (string) reader["Database"];
            i++;
            }
        }

       reader.Close();
       reader = null;
       dbcmd.Dispose();
       dbcmd = null;
       dbcon.Close();
       dbcon = null;




        Text = "School Year";
        Size = new Size(340, 240);

        cb = new ComboBox();
        cb.Parent = this;
        cb.Location = new Point(50, 30);

        cb.Items.AddRange(databases);

        cb.SelectionChangeCommitted += new EventHandler(OnChanged);

        label = new Label();
        label.Location = new Point(80, 170);
        label.Parent = this;
        label.Text = "...";

        CenterToScreen();


    }

    void OnChanged(object sender, EventArgs e) {
         ComboBox combo = (ComboBox) sender;
         label.Text = combo.Text;
    }
}


class MApplication {
    public static void Main() {
        Application.Run(new MForm());
    }
}
4

1 回答 1

1

你的逻辑不正确。我假设这些都是您不想添加到数组中的表名。

  • 假设您要排除“information_schema”。该名称不等于“sakila”，因此该名称将添加到您的数组中。
  • 此外，由于您刚刚在此之前定义了databases数组，并且其中的所有元素都是空的（或 null？），因此这些条件都不会满足。

将所有更改||为&&，并将它们与阅读器中返回的数据进行比较：

while (reader.Read())
{
    var database = reader["Database"].ToString();

    if ((database != "information_schema" && database != "sakila" &&
         database != "enrollmentsystem" && database != "mysql" &&
         database != "world" && database != "performance_schema")
    {
        databases[i] = database;
        i++;
    }
}

我认为一些 LINQ 和使用 aList<string>会使这更容易阅读。它还将消除对获取用于在数组中分配空间的计数的第一个查询的需要。

var databases = new List<string>();

var excludedDatabases =
    new List<string> { "information_schema", "sakila", "enrollmentsystem",
                       "mysql", "world", "performance_schema" };

while (reader.Read())
{
    var database = reader["Database"].ToString();

    if (!excludedDatabases.Contains(database))
        databases.Add(database);
}
于 2015-01-18T13:15:52.157 回答