C# 使用'时保持数据库连接；收益率'；

我有一个基本的数据类（为简洁起见，将其剥离并编译）：

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仅供参考，你可以使用语句来堆叠你的

，如果你想避免所有的嵌套的话，我实际上使用的是VB.NET，但是我在家，所以只需要在C中模拟一下等价的语句#
public static class Database
{
    public static IEnumerable<T> GetRecords<T>(string query, Func<IDataReader, T> mappingFunction)
    {
        var connectionString = "";
        using (var connection = new SqlConnection(connectionString)) 
        {
            using (var command = new SqlCommand(query, connection)) 
            {
                using (var reader = command.ExecuteReader(CommandBehavior.CloseConnection)) 
                {
                    while(reader.Read()) {
                        yield return mappingFunction(reader);
                    }
                }
            }
        }
    }
}

var records = Database.GetRecords("SELECT FirstName FROM [Order]", reader => 
                                          new Order { FirstName = reader["FirstName"].ToString() });

public class Order {
    public string FirstName;
}           

using (var reader = command.ExecuteReader(CommandBehavior.CloseConnection)) 
{
    var items = new List<T>();
    while(reader.Read()) {
        items.Add(mappingFunction(reader));
    }
    return items;
}

var orders = Database.GetRecords("SELECT [things] FROM [Order]", reader =>  MapOrder(reader));

IEnumerable<ReportRecord>() GetRecords(IEnumerable<Order> orders) 
{
    foreach (var order in orders) 
    {
        var reportRecord = new ReportRecord();
        var items = GetOrderItems(order);

        // other queries, calculations etc

        yield return reportRecord;
    }
}

// save to disk using CsvHelper and output file
CsvHelper.Save(GetRecords(), filepath); // fake code -- but uses the IEnumerable instead of materialised list