114 lines
8.4 KiB
HTML
114 lines
8.4 KiB
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<meta name="DC.Title" content="Visual Basic: The compromise between Jet and ODBC APIs" />
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<meta name="abstract" content="While the database objects are easy to code, they sometimes can adversely affect performance. Coding to the APIs and to stored procedures can be a frustrating endeavor. Fortunately, if you are using Visual Basic Enterprise Edition in the Windows 95 environment, there are additional options. These options are a good compromise between the usability of database objects and the high performance of APIs: Remote Data Objects (RDO) and Remote Data Control (RDC)." />
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<meta name="description" content="While the database objects are easy to code, they sometimes can adversely affect performance. Coding to the APIs and to stored procedures can be a frustrating endeavor. Fortunately, if you are using Visual Basic Enterprise Edition in the Windows 95 environment, there are additional options. These options are a good compromise between the usability of database objects and the high performance of APIs: Remote Data Objects (RDO) and Remote Data Control (RDC)." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1999, 2006" />
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<title>Visual Basic: The compromise between Jet and ODBC APIs</title>
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</head>
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<body id="vb5jetodbc"><a name="vb5jetodbc"><!-- --></a>
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<!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Visual Basic: The compromise between Jet and ODBC APIs</h1>
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<div><p>While the database objects are easy to code, they sometimes can
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adversely affect performance. Coding to the APIs and to stored procedures
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can be a frustrating endeavor. Fortunately, if you are using Visual Basic
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Enterprise Edition in the Windows<sup>®</sup> 95 environment, there are additional
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options. These options are a good compromise between the usability of database
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objects and the high performance of APIs: Remote Data Objects (RDO) and Remote
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Data Control (RDC).</p>
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<div class="section"><p>RDO is a thin layer over the ODBC APIs. It provides a simple interface
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to advanced ODBC functionality without requiring programming to the API level.
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It does not have all of the overhead of the Jet Engine controlled Data Access
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Object (DAO) or its <span class="keyword">SQL</span> optimizer.
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Yet it maintains a nearly identical programming interface as the DAOs. If
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you understand programming to the DAO, then switching over to the RDO is relatively
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simple compared to trying to switch over to API calls.</p>
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</div>
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<div class="section"><p>The following are differences between DAO and RDO: </p>
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<ul><li>The DAO model is used for ISAM, Access and ODBC databases. The RDO model
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is designed for ODBC databases only, and it has been optimized for Microsoft<sup>®</sup> <span class="keyword">SQL</span> Server 6.0 and Oracle.</li>
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<li>The RDO model can have better performance, with the processing being done
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by the server and not the local machine. Some processing is done locally with
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the DAO model, so performance may not be as good.</li>
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<li>The DAO model uses the Jet Engine. The RDO model does not use Jet Engine,
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it uses the ODBC backend engine.</li>
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<li>The RDO model has the capability to perform synchronous or asynchronous
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queries. The DAO model has limitations in performing these type of queries.</li>
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<li>The RDO model can perform complex cursors, which are limited in the DAO
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model.</li>
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</ul>
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</div>
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<div class="section"><p>The RDC is a data control similar to the standard data control.
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This means that where ever you might have used a data control, and the Jet
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engine, you now can use the RDC. You can drag a "data aware" control on your
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form. It can be bound to an RDC, as it could be bound to a regular data control.</p>
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</div>
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<div class="section"><p>Some of the advanced ODBC functionality the RDO allows is prepared <span class="keyword">SQL</span> statements, multiple result
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sets, and stored procedures. When Jet executes a <span class="keyword">SQL</span> statement
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dynamically it is a two-step process on the iSeries™ server. In the first step, the iSeries server
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looks at the statement and determines the best plan to retrieve the data requested
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based on the current database schema. In the second step, that plan is used
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to actually retrieve the data. Creating that plan can be expensive in terms
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of time because the iSeries server has to evaluate many alternatives
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and determine the best way to access the data. There is an alternative to
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forcing the iSeries server
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to recreate the access plan every time a <span class="keyword">SQL</span> statement
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is run. The <strong>CreatePreparedStatement</strong> method of the <strong>rdoConnection</strong> object
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allows you to compile a data access plan on the iSeries server for an <span class="keyword">SQL</span> statement
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without executing it. You can even include parameters in prepared statements,
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so you can pass new selection criteria every time you run the select statement.</p>
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</div>
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<div class="section"><p>The following sample Visual Basic code will show how to prepare
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a <span class="keyword">SQL</span> statement with
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a parameter marker and run it multiple times with different values.</p>
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</div>
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<div class="section"><div class="fignone"><span class="figcap">Figure 1. Visual Basic 4.0 RDO sample code</span><br /><img src="vb4001.gif" alt="VB 4.0 RDO sample code" /><br /></div>
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</div>
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<div class="section"><p>Label A shows where the <span class="keyword">SQL</span> statement
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is defined. Notice that the statement does not include a specific for the
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CUSTNUM, but has a question mark for the value. The question mark signifies
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that this value is a parameter of the prepared statement. Before you can create
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a result set with the prepared statement, you must set the value of any parameters
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in the statement.</p>
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</div>
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<div class="section"><p>Label B shows where the value for the parameter is defined. Notice
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that the first parameter is defined as 0 not as 1. Once the value for the
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parameter is set you can run the <strong>OpenResultSet</strong> method of the <strong>rdoPreapredStatement</strong> to
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return the requested data.</p>
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</div>
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<div class="section"><p>Before you can re-query a prepared statement on the iSeries server,
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you have to make sure that the cursor has been completely processed and closed.
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Label C shows the <strong>MoreResults</strong> method of the <strong>rdoResultSet</strong> being
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used to do this. The <strong>MoreResults</strong> method queries the database. It determines
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if there is any more data in the result set to be processed, or if the result
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set has been processed completely. Once the cursor has been fully processed
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you can reset the parameter value and run the <strong>ReQuery</strong> method of the <strong>rdoResultSet</strong> to
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open a new result set.</p>
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</div>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzaikdirectcodeodbcapis.htm" title="Many PC applications make ODBC calls that allow the user to seamlessly access data on different platforms. Before you begin developing your own application with ODBC APIs, you should understand how an ODBC application connects to and exchanges information with a database server.">Code directly to ODBC APIs</a></div>
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</div>
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</div>
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</body>
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</html>
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