.NET/ASP.NET/C#/VB.NET PDF Document SDK

We update an object by selecting it into memory, changing the in-memory Java object as required, and using the Java object to update the object value in the database. An important point to note is that when we select an object in memory, we don t have exclusive access to it, because in Oracle reads don t block writes. So it is possible that the changes we make are overridden by someone else who happens to be simultaneously updating the same set of rows using the same technique. This phenomenon is called lost updates. We will revisit and resolve this issue in detail in 16. To avoid lost updates, we need to lock any selected rows. We do that by using the for update nowait clause in our select statement. This tells Oracle to either lock the row for us or fail with an exception if the lock is already held by someone else updating the same row. The method _demoUpdate() illustrates this concept: private static void _demoUpdate( Connection connection ) throws SQLException { As a first step, we need to select the object using the concepts discussed in the section Selecting Objects earlier. The only major difference is that the select statement has a phrase for update nowait at the end to indicate that we want to try and lock any rows that get selected: PreparedStatement pstmt = null; PreparedStatement pstmt1 = null; ResultSet rset = null; try { MyAddress myAddress = null; String selectStmt = "select value(a) from address_table a"+ " where line1 = for update nowait"; pstmt = connection.prepareStatement ( selectStmt ); pstmt.setString( 1, "145 Apt # 7" ); rset = pstmt.executeQuery();

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ASP.NET files of the types shown in Tables 14-1 and 14-2 are located in the web application s web root directory and the various subfolders within. The standard ASP.NET folders are as follows: App_Code: Utility, application, and data access layer code basically, all source files that are not codebehind files App_Data: Database and XML files App_GlobalResources: Global resource files, such as those related to localization App_LocalResources: Resource files associated with specific controls or pages App_WebReferences: Web reference discovery files and service descriptions (wsdl) Bin: Third-party binaries, libraries these are automatically referenced in the web application

while( rset.next() ) { myAddress = (MyAddress) rset.getObject(1); After obtaining the object, we modify the street attribute (you can, of course, change any other attribute as well): myAddress.setStreet ( "Wonderful St" ); Then we update the corresponding row: String updateStmt = "update address_table a" + " set value(a) = " + " where a.line1 = "; pstmt1 = connection.prepareStatement ( updateStmt ); pstmt1.setObject (1, myAddress ); pstmt1.setString (2, "145 Apt # 7" ); int rows = pstmt1.executeUpdate(); System.out.println ( "Updated " + rows + " rows " ); } connection.commit(); } finally { JDBCUtil.close( rset ); JDBCUtil.close( pstmt ); JDBCUtil.close( pstmt1 ); } }

created them, the factory still creates all of the output parameters, which you use after executing the command This simplifies your code, but comes at the cost of an extra round trip to the database to query the schema so the factory knows what parameters to create To compensate for this, the block uses a cache to keep the definition of the parameters present in memory after the initial round trip to retrieve the metadata This means the penalty for the extra round trip is only incurred on the first request; subsequent requests will retrieve the parameters from the cache This yields better performance for subsequent requests (after the first) than the previous example, which has to re-create all of the parameter objects with each request.

The simplest websites use only HTML static content. We do not consider these in this book, though we assume you are familiar with authoring HTML. Beyond this, the building blocks of the dynamic content on ASP.NET websites are .aspx web forms (web pages). These are essentially HTML files that contain ASPX markup for server-side controls, although they are not processed as embedded scripts; instead, the page should be viewed as an object type that produces the

There is nothing special about deleting an object. It is a simple relational statement, as illustrated in the following definition of the method _demoDelete(): private static void _demoDelete( Connection connection ) throws SQLException { PreparedStatement pstmt = null; try { String deleteStmt = "delete address_table a" + " where a.line1 = "; pstmt = connection.prepareStatement ( deleteStmt ); pstmt.setString (1, "145 Apt # 7" ); int rows = pstmt.executeUpdate(); System.out.println ( "Deleted " + rows + " row(s) " ); connection.commit(); }