My struggles in understanding and learning about Object Oriented design, and the tools and knowledge I've taken from them.

Friday, January 28, 2011

Writing Code That Writes Code

This blog references an executable and source code available for download. To download the referenced executable, Click Here

To download source, Click Here

The Pragmatic Programmer, which is a really nifty book that outlines principles for how a programmer should conduct himself (or herself), tells us to "write code that writes code."

There are several reasons one would want to have code that writes code:

1. We tend to write code in a consistent way.
2. If we don't write code in a consistent way, we should
3. Because of 1 & 2, reducing the amount of lines of code we have to physically write can increase our productivity, because it takes less physical work to create more functionality.

When I'm building a database application in C#, my business logic classes often look very similar. When considering how I would build an application that would write code for me, I started by looking at the consistencies in my code. I found the following:

1. I mostly write database applications, and business classes that represent (more or less) table definitions in my database. For example, for a CRM application that manages marketing campaigns, I might have a table called "Person" that represents people in my database; I may also have a table called "MarketingCampaign" that allows me to keep track of my marketing campaigns. I may have a link table called "MarketingRecipient" that links "Person" to "MarketingCampaign" (in other words, the MarketingRecipient table has a record for each person a marketing campaign targeted). To represent these business concepts in code, I would probably build *at least* 3 classes (probably more because I'm careful to avoid violating the Open-Closed principle). But these classes would probably be: Person, MarketingCampaign, and MarketingHistory (which is a collection of MarketingCampaign objects). I don't use ORM (object-relational mapping), because I don't like to surrender as much as it seems ORM asks us to surrender for the sake of convenience.

2. Most of the business layer classes I build have a load() method and a Save() method, and they often look similar; however, not similar enough to over-rely on inheritance.

3. I often have a need to represent business layer classes as a collection. These collections often look very similar - again, not similar enough to use inheritence (IMHO).

4. I make an effort to document (comment) every private member, public attribute, constructor, and method.

5. I often have a need to have a corresponding public attribute for every private member I have. Obviously this is not always the case.

Armed with these bits of information, I embarked on building a rinky-dink code generator that suits my needs.

So, this little application looks as follows:

As you can see, this app is quite simple, and the top input control is for "Class Name". This, as you might guess, asks you to enter a class name.

In the below example, I create a class name of "Person". Once I click the "Create" button, the panel below is activated.

At this point, I can start adding attributes to the class. I can manually type in the data type I want, or there is a set of primitive types in the dropdown.

Once I'm done adding attributes to the class, I click the "Generate Code" button in the lower right corner:

And voila - we have code. Granted, there's not a ton of functionality or code smarts this buys me, but it does do the following:

1. It does quite a bit of typing of members and attributes - this can be a big time saver when talking about 10-50 classes being created
2. It comments for me. Maybe not the best comments, but I like to comment all my members, attributes, and methods
3. It saves me from having to rewrite the same things over and over again, which helps me to abide by the "Don't repeat yourself" principle.

Granted, I often have to change things that are producted from this little app, but as mentioned above, this little app has turned out to be a big time saver. I'm sure there are better code generators out there, but for now, this works for me.

To download the referenced executable, Click Here

To download source, Click Here
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