我是在课内还是课外编写这些 using 语句？

Question

我编写了一个类，其中包含对从我的数据库中提取的数据执行计算的不同方法。每个方法都从数据库中提取信息并对其执行计算，然后将其保存到类中的一个变量中，当我初始化类时可以访问该变量。我在下面有两种伪代码方法，我正在尝试找出以下内容：

1. 如果每个方法都提取数据然后对其执行计算，我应该以哪种方式使用 using 语句？
2. 我是否使用最有效的方式来存储数据？

这是我在初始化类时所做的

    public class Calculations
    {
    public string Symbol { get; set; }
    public string Market { get; set; }
    public List<decimal> stockPctReturns { get; set; }
    public List<decimal> marketPctReturns { get; set; }
    public enum returnType { Market, Stock };
    public decimal avgAnnualMarketGrowth { get; set; }
    public List<decimal> stockPctGains { get; set; }
    public List<decimal> stockPctLosses { get; set; }
    public List<decimal> positiveMoneyFlow { get; set; }
    public List<decimal> negativeMoneyFlow { get; set; }
    public decimal rsi { get; set; }
    public decimal mfi { get; set; }
    public decimal williamsR { get; set; }
    public decimal sma20 { get; set; }
    public decimal sma50 { get; set; }
    public decimal sma200 { get; set; }
    public const decimal riskFree10Yr = 2.58M;

    public Calculations(string symbol, string market)
    {
        // initialize everything in the class
        Symbol = symbol;
        Market = market;
    }
}

这样做：

public void fillPctReturns()
    {
        stockPctReturns = new List<decimal>();
        marketPctReturns = new List<decimal>();

        using (DailyGlobalDataTableAdapter dailyGlobalAdapter = new DailyGlobalDataTableAdapter())
        using (DailyAmexDataTableAdapter dailyAmexAdapter = new DailyAmexDataTableAdapter())
        using (DailyGlobalDataTable dailyGlobalTable = new DailyGlobalDataTable())
        using (DailyAmexDataDataTable dailyAmexTable = new DailyAmexDataDataTable())
        {
            dailyAmexAdapter.Fill(dailyAmexTable);
            dailyGlobalAdapter.Fill(dailyGlobalTable);
                    var amexQuery = from c in dailyGlobalTable.AsEnumerable()
                                    where c.Date >= DateTime.Now.Subtract(TimeSpan.FromDays(60))
                                    orderby c.Date descending
                                    join d in dailyAmexTable.AsEnumerable() on c.Date equals d.Date
                                    select new StockMarketCompare { stockClose = d.AdjustedClose, marketClose = c.AdjustedClose };

                    List<StockMarketCompare> amexResult = amexQuery.ToList();
// perform calculations here and save to stockPctReturns and marketPctReturns
         }
  }

或者我应该这样做：

using (DailyGlobalDataTableAdapter dailyGlobalAdapter = new DailyGlobalDataTableAdapter())
        using (DailyAmexDataTableAdapter dailyAmexAdapter = new DailyAmexDataTableAdapter())
        {
            Calculations calc = new Calculations();
            calc.Symbol = "GOOG";
            calc.Market = "nyse";
            dailyAmexAdapter.Fill(calc.dailyAmexTable);
            dailyGlobalAdapter.Fill(calc.dailyGlobalTable);
            calc.fillPctReturns();
        }

// 这个例子在数据表的计算类中有公共属性，你可以看到我像上面那样设置它们

希望你能说出我想要做什么。

Answer 1

看起来您展示的第二种方法现在允许您将 dailyAmexTable 和 dailyGlobalTable 包装在 using 块中，因此，如果它们各自的类实现 IDisposable（我假设它们基于您的其他代码），那么我更喜欢第一种方法。这允许您将所有 IDisposable 实例包装在 using 块中，您应该这样做。

使用块的主要问题是，您通常希望在不再需要它们时立即关闭它们以释放资源。因此，您应该尝试在 using 块之外进行计算，除非您需要在执行计算后将某些内容保存回数据库。所以它看起来像这样：

public void fillPctReturns()
{
    stockPctReturns = new List<decimal>();
    marketPctReturns = new List<decimal>();

    // Declare amexResult here so it is accessible outside the using block
    List<StockMarketCompare> amexResult;

    using (DailyGlobalDataTableAdapter dailyGlobalAdapter = new DailyGlobalDataTableAdapter())
    using (DailyAmexDataTableAdapter dailyAmexAdapter = new DailyAmexDataTableAdapter())
    using (DailyGlobalDataTable dailyGlobalTable = new DailyGlobalDataTable())
    using (DailyAmexDataDataTable dailyAmexTable = new DailyAmexDataDataTable())
    {
        dailyAmexAdapter.Fill(dailyAmexTable);
        dailyGlobalAdapter.Fill(dailyGlobalTable);
        var amexQuery = from c in dailyGlobalTable.AsEnumerable()
                        where c.Date >= DateTime.Now.Subtract(TimeSpan.FromDays(60))
                        orderby c.Date descending
                        join d in dailyAmexTable.AsEnumerable() on c.Date equals d.Date
                        select new StockMarketCompare { stockClose = d.AdjustedClose, marketClose = c.AdjustedClose };

        amexResult = amexQuery.ToList();

     }
     // perform calculations here and save to stockPctReturns and marketPctReturns
}

编辑：

现在我更清楚地看到了你在做什么，我建议在课堂之外使用 using 块。主要原因是确保您的代码是松散耦合，在这种情况下意味着数据访问代码与业务逻辑是分开的（又名计算）代码。一种方法是在计算类之外运行查询，并将查询结果传递给计算类中的属性。例如：

public class Calculations
{
    public List<StockMarketCompare> Data { get; set; }
    // (Other properties and methods omitted.)
}

然后在你的调用函数中：

var calc = new Calculations();
using (DailyGlobalDataTableAdapter dailyGlobalAdapter = new DailyGlobalDataTableAdapter())
using (DailyAmexDataTableAdapter dailyAmexAdapter = new DailyAmexDataTableAdapter())
using (DailyGlobalDataTable dailyGlobalTable = new DailyGlobalDataTable())
using (DailyAmexDataDataTable dailyAmexTable = new DailyAmexDataDataTable())
{
    dailyAmexAdapter.Fill(dailyAmexTable);
    dailyGlobalAdapter.Fill(dailyGlobalTable);
    var amexQuery = from c in dailyGlobalTable.AsEnumerable()
                    where c.Date >= DateTime.Now.Subtract(TimeSpan.FromDays(60))
                    orderby c.Date descending
                    join d in dailyAmexTable.AsEnumerable() on c.Date equals d.Date
                    select new StockMarketCompare { stockClose = d.AdjustedClose, marketClose = c.AdjustedClose };

    calc.Data = amexQuery.ToList();
    calc.fillPctReturns();
    // Run any other calculations here.
    // Save data to DB here.
}