ASP.NET Web PDF Document Viewer/Editor Control Library

length;; val it : int = 1 However, be aware that these additional transformations are happening in-memory and not on the database The command object has different methods for executing different queries For instance, if you have a nonselect query, you need to use the ExecuteNonQuery method (for UPDATE, INSERT, or DELETE statements, like previously in execNonQuery), which returns the number of rows affected (updated, inserted, or deleted), or the ExecuteScalar method, which returns the first column of the first row of the result providing a fast and efficient way to extract a single value, such as the number of rows in a table or a result set..

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To create any of the six combinations of result sets, you can use one of the following methods in the Connection object: Statement createStatement (int resultSetType, int resultSetConcurrency) PreparedStatement prepareStatement(String sql, int resultSetType, int resultSetConcurrency) CallableStatement prepareCall(String sql, int resultSetType, int resultSetConcurrency) As mentioned earlier, although the Oracle JDBC documentation states that the result set scrollability and updatability are implemented in CallableStatement, I discovered that the current implementation does not work for result sets returned via stored procedures. This is not a real problem since updatability, as implemented currently, can be easily accomplished using standard SQL statements to update, insert, and delete rows. As far as scrollable result sets go, their most common use is to display a subset of rows at a time for a given result set and allow the user to scroll through it, say, ten rows at a time. For this scenario, as explained in

ERROR at line 1: ORA-02292: integrity constraint (BENCHMARK.SYS_C006564) violated child record found If you use references, you should always create a referential integrity constraint as just shown to avoid the problem of dangling references in your application data.

In the previous command, we extracted fields from the result rows using GetXXX methods on the reader object. The particular methods have to match the types of the fields selected in the SQL query, and a mismatch will result in a runtime InvalidCastException. For these and other reasons, DataReader tends to be suitable only in situations when the following items are true: You need to read data only in a sequential order (as returned from the database). DataReader provides forward-only data access. The field types of the result are known, and the query is not configurable. You are reading only and not writing data. DataReader provides read-only access. Your use of the DataReader is localized. The data connection is open throughout the reader loop.

Figure 2-4. The CreateSessionVars page on its third rendering By trapping the AcquireRequestState while preprocessing the page, you can keep track of how many Session variables are created during the lifetime of the request, regardless of where they re created. In this simple example you re only creating them in the Button Click event trap, but this pattern works even if you re creating or destroying Session variables in other preprocessors. The next event is PreRequestHandlerExecute. As you ll see in just a bit, any piece of code can process requests that come into the ASP .NET Framework by implementing the IHttpHandler interface. The main task in implementing this interface is to provide code

Always create a referential integrity constraints for any reference columns you use in your schema to Tip

Database connections are precious resources, and you should always release them as soon as possible. In the previous case, we did this by using a locally defined connection. It is also sufficient to implicitly close the reader by constructing it with the CloseConnection option that causes it to release and close the data connection upon closing the reader instance. Further, common options include SchemaOnly that you can use to extract field information only (without any data returned), SingleResult to extract a single value only (the same as using the ExecuteScalar method discussed earlier), SingleRow to extract a single row, and KeyInfo to extract additional columns (appended to the end of the selected ones) automatically that uniquely identify the rows returned.