Real World Object-Oriented Development with ASP.NET: A Custom Data Class
This chapter is from the book
This chapter is from the book
This chapter is from the book
In Chapter 1, "The Object Model," I gave you an analogy that compares the concept of a class to that of a car. A class encapsulates some kind of functionality into one neat and simple package.
Many Web coders who have used other platforms such as PHP or Cold Fusion are a little surprised at the number of steps required to get data in and out of a database in .NET. Just to get a few values out of the database, you need to create a connection object, a command object, and then at the very least a DataReader. (In all fairness, you get back much of your time when data binding!) Sounds like the perfect place to build a useful class!
If we put all of our database logic into one class, we can write the SQL statements once and manipulate the data with far less code throughout our application. You'll also benefit from having just one place to change code if you decide to use a different database (such as Oracle). Best of all, implementing a data-caching scheme is that much easier when all of your data code is in one place.
To help you see the benefit of this write-once, use-everywhere class, Listing 5.1 shows a code sample that creates a row in our database, reads the row, and then deletes it, all via a class that we'll build in this chapter.
Example 5.1. A class in action
C#
// Instantiate the Customer class using the default constructor
Customer customer = new Customer();
// Assign some of its properties
customer.LastName = "Jones";
customer.FirstName = "Jeff";
// Call its Create() method to save the values in the database,
// and get its new primary key (CustomerID) value
int customerID = customer.Create();
// Instantiate the Customer class using the constructor that takes
// the CustomerID as a parameter
Customer customer2 = new Customer(customerID);
Trace.Write("LastName: " + customer2.LastName);
Trace.Write("FirstName: " + customer2.FirstName);
// Change the value of the first name then save the changes
// to the database
customer2.FirstName = "Stephanie";
customer2.Update();
// On second thought, let's just delete the record entirely
customer2.Delete();
VB.NET
' Instantiate the Customer class using the default constructor
Dim customer As New Customer()
' Assign some of its properties
customer.LastName = "Jones"
customer.FirstName = "Jeff"
' Call its Create() method to save the values in the database,
' and get its new primary key (CustomerID) value
Dim customerID As Integer = customer.Create()
' Instantiate the Customer class using the constructor that takes
' the CustomerID as a parameter
Dim customer2 As New Customer(customerID)
Trace.Write(("LastName: " + customer2.LastName))
Trace.Write(("FirstName: " + customer2.FirstName))
' Change the value of the first name then save the changes
' to the database
customer2.FirstName = "Stephanie"
customer2.Update()
' On second thought, let's just delete the record entirely
customer2.Delete()
You can see by these few lines of code that we didn't go through the entire process of creating connection, command, and other data objects. A few simple method calls are all we need to manipulate the data. Imagine how much time you'd save if you had to manipulate the data in dozens of places around your application!
Analyzing Design Requirements
The first step in designing any class is to identify your needs in human terms before writing code. In our case, we want to make it easy to get, update, and delete data from a table called Customers in SQL Server. None of the columns in our table allows null values.
Table 5.1. The Customers table
|
CustomerID (primary key/identity) |
int |
|
LastName |
nvarchar |
|
FirstName |
nvarchar |
|
Address |
nvarchar |
|
City |
nvarchar |
|
State |
nvarchar |
|
Zip |
nvarchar |
|
Phone |
nvarchar |
|
SignUpDate |
datetime |
We know that the Customers table has nine columns that we can manipulate. We also know that we want to create, update, and delete records in this table. The most obvious need we'll have is to get data from the table. After we have the basics of our class nailed down, we'll revise the class to cache data and explore ways to get a number of records at one time.