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If we expect that categories are already cached in the session or second-level cache, then we only need the identifier value (the key to the cache). This will reduce the amount of data we have to fetch from the database. The following SQL would be slightly more efficient:

It should be obvious what listing 2.26 does. Starting with a sequence of 1 through 10, plus another 10, the first delete operation removes the first index, the second deletes a range from index positions 0 to 2 (inclusive), the third removes any tens from the sequence, and the final delete removes the entire sequence. One final trick is the ability to reverse the order of a sequence, as shown here.

You should be careful of adding too many constructors to a class or struct. It is easy to lose track of which parameters are which, or to make arbitrary choices about which constructors you provide and which you don t. For example, let s say we wanted to add yet another constructor to PolarPoint3D that lets callers pass just the angle and altitude, initializing the distance to a default of zero, as Example 3-31 shows.

Chunk.NEWLINE contains a newline character in the default font; and the default font is Helvetica. You could have avoided this by replacing that line with this one:

A WHERE clause in a query containing both the GROUP BY and HAVING clauses results in multistage processing. First, the WHERE clause is applied to filter the results. Then, the results are aggregated based on the GROUP BY clause. Finally, the HAVING clause is applied to filter the aggregated result.

Our service is designed to let people chat, so it will need to provide clients with a way to send a short bit of text, which we ll refer to as a note. (A more obvious name would be message, but that would introduce ambiguity WCF sends messages to and from the server for every operation, so to call one of the pieces of information that crops up

The login() method in listing 11.2 provides the details on authentication. We extract the username and password from the request g and then invoke findUser(), which contacts the database for a matching row i. (We ve abstracted away the details of the database behind a DBUtil object here.) If a row matching the user is found, the function returns a User object j, which is then stored in session h for the next time we pass through this filter. On subsequent passes through this filter, we won t need to provide the username and password in the querystring, because the User object will already be in session.

Invoke Method(s)

Yup; we re no better off than before, because all we ve done is to pass the responsibility up to the client, and they are still free to ignore our pleadings. Given that the problem is a result of our oversight in the first place, what is the likelihood that we ll remember to check the error message Things would be even worse if this was in a library; we could recompile against this new version, and everything would seem fine, while in the background everything would quietly be going horribly wrong. It is probably about time we did something with the error message, so let s see what happens in our client code (see Example 6-10).

In this example, the Employee IDs start at 1005 and proceed from there. You see that you need to create each Employee object with the new keyword in the for loop. To access the EmpID member of each Employee object, you use the dot notation: empArray[i].EmpID. Notice that the dot comes after the square brackets. Remember that empArray represents the entire array, but empArray[i] represents a single Employee, so you can access the member fields and methods of each individual object.

public class Address { ... @OneToOne(mappedBy = "shippingAddress") private User user; ... }