Saturday, April 24, 2010

Violating Single Resposibility Principle using VisualStudio Region

Single Responsibility Principle (SRP)says that "THERE SHOULD NEVER BE MORE THAN ONE REASON FOR A CLASS TO CHANGE.". Although this article mentions only about class, I think the SRP also applies to methods within the class: there should never be more than one reason for a method to change.

Visual Studio provides a good way to mark off section of file in the form of "region"so they can be collapsible and the code can be organized. Many people use region in a big method to organize the code. For example:
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public void CreeateOrder(/*some parameters*/)
{
    #region Validate the parameters
    //code goes here
    #endregion
 
    #region create the order
    //insert the order data in the database
    #endregion
 
    #region create the order item
    //insert the item data in the database
    #endregion
}
Note that not all people use regions like this. Many people use comments instead of regions in this kind of methods.

As you can see this is a clear violation of the single responsibility principle. The method does more than one thing: it validates the order data, create a top level order and create order items. This can certainly be put into separate method.

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private bool ValidateOrderData(/*some parameters*/)
{
    #region Validate the parameters
    //code goes here
    #endregion
}
 
private bool InsertOrder(/*order related parameter*/)
{
    #region create the order
    //insert the order data in the database
    #endregion
}
 
private bool InsertOrderItem(/*order item related parameter*/)
{
    #region create the order item
    //insert the item data in the database
    #endregion
}
 
public  void CreateOrder(/*Some parameter*/)
{
    If(ValidateOrder(/*parameter list*/))
    {
        if(InsertOrder(/*order parameter*/))
        {
            InsertOrderItem(/*order item parameter*/);
        }  
    }
}

As you can see, wherever you are using "region" in your method to demarcate the code, you can very well put that code in a separate method.