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for the ProcessRequest method This is the last preprocessing event that fires before the ProcessRequest method is called on the handler It s your last chance to do any pre-processing, before the code from your Page object starts executing Almost everything is available to you from this event The context has been long established, so the Request, Response, Cache, and Cookies are all available Session state has been restored and is available Plus, the context handler has been created and the HttpContextHandler property has exposed an instance of it In the case of Page processing, the only thing not available at this point are the values ViewState restores, as those don t move from the Post variables to the protected instance variables until the page is initialized.

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There are many reasons why you should avoid references, in general. Since references ultimately point to object rows in tables, all the reasons to avoid objects as a storage mechanism are applicable to references as well (as discussed in the section Using Objects to Store Data [Not Recommended] of 8). The following are some additional reasons for you to consider: References can complicate your code considerably. For example, if you want to write a hierarchical query that retrieves all child and parent records in a table, you can do so easily using the connect by clause for a traditional parent/child table. But if you use references instead, you will have to dereference each record separately, resulting in complicated and slow code. References result in extra information being stored in tables (see the section Storage Size of Refs in 8 of Oracle Database Application Developer s Guide Object Relational Features (10g Release 1). This takes up extra space, which you can avoid by adopting a design that uses simple parent/child relational tables. Performing DML operations with references can be complex and result in slow-running code, as you ll see shortly. In return for all the complexity and performance degradation, you don t get any particular benefit when using references. That discussion concludes the brief introduction to references. Even though references are not a very useful feature for the reasons mentioned in this section, we ll cover JDBC access techniques for completeness and so that you can deal with them if you encounter them in code. In the next section, we ll examine how you can use references in your JDBC code.

Datasets allow applications to work in a so-called disconnected mode, which means the application connects to the database, loads relevant data to an in-memory representation, and processes the data locally. When the processing is completed, the data in the in-memory dataset can be synchronized with the database. ADO.NET datasets are compact in-memory databases and provide similar functionality to real databases; however, they are designed to work with a limited amount of data. A DataSet contains a collection of tables, the relationships between those tables, and various constraints. Tables are represented by the DataTable type. And like in a SQL server, tables are defined by their columns (DataColumn objects), and the data is stored in rows (DataRow objects). In ADO.NET, the loading of data to the dataset and the synchronization to the database are coordinated by data adapters, for instance, SqlDataAdapter objects. Consider the following example in which we define a buildDataSet function that takes a connection and a SQL SELECT query and returns the resulting DataSet object:

As in the case of object types and collections, Oracle gives you the option of using weakly typed reference classes (java.sql.Ref or oracle.sql.REF) in your JDBC application. You can also use custom classes created by the now familiar utility JPublisher. In the next two sections we ll look at both options. We ll begin with a discussion of how to use weakly typed Ref and REF interfaces to query references in your JDBC programs.