SQL Server 2008 CLR聚合函数

Question

我一直在寻找使用CLR聚合来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这个主题的文章和很多的小技巧，我还是不太明白。

我的输入是一系列的日期和价值观，我希望能够做到以下几点：

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

这是到目前为止我的代码：

[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); 
     } 
    } 
} 

如何顺利拿到将SQL查询中的数据放入List<Transaction>以便我可以处理它并返回计算的值？

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;}} 
} 

那么，我想那是你真正想要看起来是这样的：

[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()); 
     } 
    } 
}