strategy_pattern

---

---

Strategy pattern - The strategy pattern (also known as the policy pattern) is a software design pattern, whereby an algorithm's behavior can be selected at run time. Formally speaking, the strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it.

In the pseudo-code example below, the Command pattern sets the parameters and sql for each unique run. What is actually run at run time is determined organically. [workflow].[run] executes each <sql> object that it is passed with no knowledge of the actual implementation.</sql>

---

Command pattern using [xml]
- command object
- receiver object

    declare @command [xml] = 
    N'<command>
        <receiver>
            <parameters>@output [xml] output</parameters>
            <sql>select @output = (<select statement> 
                for xml path(output'), root(N'output_tree'));</sql>
        </receiver>
    </command>';

---

Setter / Run
- invoker object

    declare procedure [workflow].[run] @workflow [xml], @output [xml] output
    as
        if (@workflow  is not null)
            execute sp_execute
                @sql=@workflow.value(N'(/command/receiver/sql/text())[1]', 
                    N'[nvarchar](max)'),
                @parameters=@workflow.value(
                    N'(/command/receiver/parameters/text())[1]', N'[nvarchar](max)'),
                @output=@output output;
    go

---

---

copyright Katherine Elizabeth Lightsey 1959-2013 (aka; my life)

"Always forgive your enemies; nothing annoys them so much." - Oscar Wilde

---

---