Saturday, June 30, 2012

Programming with Database: Using Prepared Statements in whole program

I have blogged several times about the benefits of programming with prepared statements when using database connections (About prepared statements, MySQL's prepared statements made easy, About SQL Injection).

But this time, I will focus on development time, and another advantages that using prepared statements give to programmers rather than its security or performance (for that you can read the other blog posts stated above).

As I stated in other posts, I recommend everyone who uses a database, to make use of Prepared Statements everywhere, not only in certain parts where you are interested.

That way, combined with Model View Controller design (MVC), can save you a lot of time and problems when database scheme changes over time (and make sure it will despite you may not think).

I am talking of common cleaning that a database may suffer some time after it has been used for some time: For example, field removal on a table, table rename, table removal, etc...

To reflect the time you can save when that happens with Prepared Statements, let's start with a very simple example and watch how it could be solved from 2 different points of view: Using prepared statements, and not using them.

Suppose we have a table called Customers with this schema (using PostgreSQL):

Column NameColumn Type

Having this table amongst others, and in a running company with plenty of data inside, now, some time after the initial database schema, we decide to switch to paypal payments processing (just an example).
In this case, having credit card info of our clients is not longer relevant, and should be deleted due to security issues.
Then now we need something like:
ALTER TABLE Customers DEL COLUMN credit_card_no;
Unfortunatelly, we are not done yet, as we need to change some parts.
As part of this example, we will see what would happen in 2 cases: 

Using MVC and Prepared Statements:
Now that we have changed database scheme, the changes that are need to be made in source code are very easy to find. If we used something like the database class I blogged here, we just need to open the browser and wait for the errors it will come out, since all SQL sentences are prepared and loaded with database initialization.
It will tell us exactly which prepared statement failed, and just a seach will show in which function member we are using it, allowing us to change it.
Once changed, you just have to be sure to change the model class which receives that old data to remove it.

Not using MVC and not using Prepared Statements:
In this scenario, the changes that needs to be done are not easy to find as we don't have any mechanism to look at every SQL sentence we have in the whole program at once.
So we should to do a seach on every project's file, and do as much as replacements we need in order to achieve the changes, and thus, more time programming which may mean more money.

So to sum up, I will render a table containing most important things about each others to reflect why is so important to use Prepared Statements rather than SQL statements as strings defined at runtime.

MVC and Prepared StatementsSQL statements on the fly
Changes find timeImmediateSearch every project's file
Number of files/classes to modify2 (Database and Model classes)Undefined (as it may be in use from several files)
Possibility of runtime errorsNo (as SQL sentence is not loaded with errors)Yes (If, for example, you forgot to change a SQL sentence which is based on strings concatenation)

So now you know that programming with prepared statements does not only protects us from SQL Injection, give us more performance, prevents from having dangerous runtime errors that may harm our public image to our customers and makes us save tons of time when things changes, why are you still not using them in your whole project?

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