Question

我制作了一个程序，它使用OleDbDataReader读取数据库中的数据，但问题是我有不同的表，这些代码工作正常，但我发现它有点“硬编码”或{{1}这是我的示例代码

recursive

我需要一次又一次地重复这一点，只是为了阅读另一张桌子上的内容（例如，private void loadMilk() { cn.Open(); OleDbDataReader reader = null; OleDbCommand cmd = new OleDbCommand("select* from Milk", cn); reader = cmd.ExecuteReader(); while (reader.Read()) { Milk.Add(reader["Product"].ToString()); } cn.Close(); }然后"select* from Fruit ....）有什么办法让我不再重复这段代码一次又一次？感谢：）

Answer 1

您可以将该方法重构为以下内容：

private IList<string> Load(string tableName, string columnName)
{
    var result = new List<string>();
    cn.Open();
    OleDbDataReader reader = null;
    OleDbCommand cmd = new OleDbCommand(string.Format("select* from {0}", tableName), cn);
    reader = cmd.ExecuteReader();
    while (reader.Read())
    {
        result.Add(reader[columnName].ToString());
    }
    cn.Close();

    return result;
}

您的代码示例将是：

var milkItems = Load("Milk", "Product");
var classicItems = Load("Classics", "..."); //Enter the column here.

修改：

您可能想要更具体的内容（例如，存储List<SomeObject>而不仅仅是List<string>）。假设您有时想要返回Person列表，并且还想阅读Building列表。然后你可以写这样的东西（未编译和测试）：

private IList<T> Load<T>(string tableName, Func<OleDbDataReader, T> selector) { IList<T> result = new List<T>(); cn.Open(); OleDbDataReader reader = null; OleDbCommand cmd = new OleDbCommand(string.Format("select* from {0}", tableName), cn); reader = cmd.ExecuteReader(); while (reader.Read()) { result.Add(selector(reader)); } cn.Close(); return result; }

你可以这样称呼：

Func<OleDbDataReader, Person> selector = x => new Person { Name = x["Person"].ToString() }; Load("People", selector);

Answer 2

private void loadMilk(string TableName, string itemValue)
        {
            string SQLString = String.Format("select * from {0}",TableName);

            cn.Open();
            OleDbDataReader reader = null;
            OleDbCommand cmd = new OleDbCommand(SQLString, cn);
            reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                Milk.Add(reader[ItemValue].ToString());
            }
            cn.Close();
        }

Answer 3

不确定“Milk”是什么类型。尝试：

private void loadObjectsFrom(string tableName, object obj, string column)
        {
            cn.Open();
            OleDbDataReader reader = null;
            OleDbCommand cmd = new OleDbCommand("select* from " + tableName, cn);
            reader = cmd.ExecuteReader();
            while (reader.Read())
            {
                obj.Add(reader[column].ToString());
            }
            cn.Close();
        }

Answer 4

只需将表名作为参数传递：

    private void loadMilk(string tableName)
    {
        cn.Open();
        OleDbDataReader reader = null;
        OleDbCommand cmd = new OleDbCommand(string.Format("select* from {0}",tableName), cn);
        reader = cmd.ExecuteReader();
        while (reader.Read())
        {
            Milk.Add(reader["Product"].ToString());
        }
        cn.Close();
    }

简化OleDbDataReader代码

4 个答案: