SQL Server 2008 CLR 聚合函数

Question

我一直在研究使用 CLR 聚合对一系列数据执行一些复杂的财务计算，但是尽管阅读了很多关于该主题的文章并且进行了很多摆弄，但我还是无法弄清楚。

我的输入是一系列日期和值，我希望能够执行以下操作：

SELECT dbo.FinancialCalc(amount, date)
FROM (VALUES
            (-100000, '11/30/2011'),
            (-50000, '3/15/2012'),
            (-2500, '7/18/2012')         
            ) n(amount, date)

到目前为止，这是我的代码：

[SqlUserDefinedAggregate(Format.UserDefined, MaxByteSize = 8000, Name = "FinancialCalc", IsInvariantToDuplicates = false, IsInvariantToNulls = true, IsInvariantToOrder = true, IsNullIfEmpty = true)]
[Serializable]
[StructLayout(LayoutKind.Sequential)]
public class FinancialCalc : IBinarySerialize
{    
    private List<Transaction> transactions;
    private List<DateTime> dates;
    private List<Double> values;

    public void Init()
    {        
        this.transactions = new List<Transaction>();
        this.dates = new List<DateTime>();
        this.values = new List<double>();
    }

    public void Accumulate(SqlDouble amount, SqlDateTime date)
    {
        this.dates.Add(date.Value);
        this.values.Add(amount.Value);
    }

    public void Merge(FinancialCalc Group)
    {
       //is this needed?
    }

    public SqlDouble Terminate()
    {
       //here is where I would do the calc: return transactions.Calculate() or somethine
        return values.Sum();
    }

    public void Read(System.IO.BinaryReader r)
    {
        int itemCount = r.ReadInt16();

        for (int i = 0; i <= itemCount - 1; i++)
        {
            this.values.Add(r.ReadDouble());          
        }
    }

    public void Write(System.IO.BinaryWriter w)
    {
        w.Write(this.values.Count);
        foreach (double s in this.values)
        {
            w.Write(s);
        }
    }
}

如何将SQL查询中的数据成功拿到List<Transaction>中，以便处理并返回计算值？

Answer 1

如果我假设 Transaction 看起来像这样：

public class Transaction
{
  private readonly double _amount;
  private readonly DateTime _date;
  public Transaction(double amount,DateTime date){
    _amount = amount;
    _date = date;
  }
  public double Amount {get{return _amount;}}
  public DateTime Date {get{return _date;}}
}

然后我假设你真正想要的看起来像这样：

[SqlUserDefinedAggregate(Format.UserDefined,
        //Play it safe, we don't know how large we'll get
        MaxByteSize = -1,
        Name = "FinancialCalc", IsInvariantToDuplicates = false,
        IsInvariantToNulls = true, IsInvariantToOrder = true,
        IsNullIfEmpty = true)]
[Serializable]
[StructLayout(LayoutKind.Sequential)]
public class FinancialCalc : IBinarySerialize
{    
    private List<Transaction> transactions;

    public void Init()
    {        
        this.transactions = new List<Transaction>();
    }

    public void Accumulate(SqlDouble amount, SqlDateTime date)
    {
        this.transactions.Add(new Transaction(date.Value,amount.Value));
    }

    public void Merge(FinancialCalc Group)
    {
       //Yes, you do need this. Group contains another set of transactions
       //and is going to disappear after this method has been called
       this.transactions.AddRange(Group.transactions);
    }

    public SqlDouble Terminate()
    {
        //Do your calculation based on the content of transactions
        return new SqlDouble(transactions.Sum(t=>t.Amount));
    }

    public void Read(System.IO.BinaryReader r)
    {
        int itemCount = r.ReadInt16();

        for (int i = 0; i <= itemCount - 1; i++)
        {
            this.transactions.Add(new Transaction(r.ReadDouble(),
                                       new DateTime(r.ReadInt64()));          
        }
    }

    public void Write(System.IO.BinaryWriter w)
    {
        w.Write(this.transactions.Count);
        foreach (var t in this.transactions)
        {
            w.Write(t.Amount);
            w.Write(t.Date.ToBinary());
        }
    }
}