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Notice how we re able to initialize the field to a default value right where we declare it, by using the = operator. (This sort of code is called, predictably enough, a field initializer.) Alternatively, we could have initialized it inside a constructor, but if the default is a constant value, it is conventional to set it at the point of declaration. What about the first example of a field that we saw the one we used as the backing data for a property in Example 3-12 We didn t explicitly initialize it. In some other languages that would be a ghastly mistake. (Failure to initialize fields correctly is a major source of bugs in C++, for example.) Fortunately, the designers of .NET decided that the trade-off between performance and robustness wasn t worth the pain, and kindly initialize all fields to a default value for us numeric fields are set to zero and fields of other types get whatever the nearest equivalent of zero is. (Boolean fields are initialized to false, for example.)

You have just witnessed the mechanism that will bring your build files to life: allowing them to adapt to user preferences, environment conditions, provide mapping indirections, and scaling to large multi-build-file processes.

The child must be added to the childCategories collection of the new par-

reportForm.StartReport("Library.ReportPatronFines.rdlc", _ "Library_ReportSchemaPatronFines", reportData)

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Once the datagram is created, the buffer must be populated with data. Datagrams only deal with data in a byte form. Below we create a String and convert it to a byte array. Once we have a byte array of data, this data can be placed into the datagram using the setData() method.

This XML document lists orders linked to that customer:

Let s take a moment to consider what we ve accomplished so far. We ve written a helper class called XSLTHelper, which encapsulates the hard-earned knowledge of providing XSLT support on the browser client. We ve taken advantage of that helper in our live search component. We ve written a simple yet generic configurable live search component that can take just a few pieces of information and transform the user s web page into a responsive searching animal. We ve written our component in a clean OO style that exemplifies simple design and separation of responsibilities. Overall, not bad for a day s work.

We could save a new instance using this code:

Let s look at the output of this program in Microsoft Internet Explorer and Mozilla Firefox, respectively. Note that the sequence of readyStates is different, but the end result is the same. The important point is that the fine details of the readyState shouldn t be relied on in a cross-browser program (or indeed, one that is expected to support multiple versions of the same browser). Here is the output in Microsoft Internet Explorer:

The ASP.NET AJAX CTP-enabled Website template creates the following files:

How does the persistence logic interact at runtime with the objects of the business domain This is a problem of generic programming, and there are a number of solutions including source generation, runtime reflection, runtime bytecode generation, and build-time bytecode enhancement. The solution to this problem may affect your build process (but, preferably, shouldn t otherwise affect you as a user). What is the lifecycle of a persistent object Does the lifecycle of some objects depend upon the lifecycle of other associated objects How do we translate the lifecycle of an object to the lifecycle of a database row What facilities are provided for sorting, searching, and aggregating The application could do some of these things in memory, but efficient use of relational technology requires that this work often be performed by the database. How do we efficiently retrieve data with associations Efficient access to relational data is usually accomplished via table joins. Object-oriented applications usually access data by navigating an object network. Two data access patterns should be avoided when possible: the n+1 selects problem, and its complement, the Cartesian product problem (fetching too much data in a single select).

public class User { private String username; private String name; private String address; private Set billingDetails; // Accessor methods (getter/setter), business methods, etc. ... } public class BillingDetails { private String accountNumber; private String accountName; private String accountType; private User user; // Accessor methods (getter/setter), business methods, etc. ... } Figure 1.1 A simple UML class diagram of the User and BillingDetails entities