176 lines
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HTML
176 lines
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<meta name="abstract" content="This topic discusses ResultSet characteristics such ResultSet types, concurrency, ability to close the ResultSet by committing the connection object, and specification of ResultSet characteristics." />
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<title>ResultSet characteristics</title>
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</head>
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<body id="rsltchar"><a name="rsltchar"><!-- --></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">ResultSet characteristics</h1>
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<div><p>This topic discusses ResultSet characteristics such ResultSet types,
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concurrency, ability to close the ResultSet by committing the connection object,
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and specification of ResultSet characteristics.</p>
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<p>By default, all created ResultSets have a type of forward only, a concurrency
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of read only, and cursors are held over commit boundaries. An exception to
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this is that WebSphere<sup>®</sup> currently
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changes the cursor holdability default so that cursors are implicitly closed
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when committed. These characteristics are configurable through methods that
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are accessible on Statement, PreparedStatement, and CallableStatement objects.</p>
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<div class="section"><h4 class="sectiontitle">ResultSet types</h4><p>The ResultSet type specifies the
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following about the ResultSet:</p>
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<ul><li>Whether the ResultSet is scrollable.</li>
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<li>The types of Java™ Database Connectivity (JDBC) ResultSets that are
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defined by constants on the ResultSet interface.</li>
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</ul>
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<p>Definitions of these ResultSet types are as follows:</p>
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<dl><dt class="dlterm"><strong>TYPE_FORWARD_ONLY</strong></dt>
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<dd>A cursor that can only be used to process from the beginning of a ResultSet
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to the end of it. This is the default type.</dd>
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</dl>
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<dl><dt class="dlterm"><strong>TYPE_SCROLL_INSENSITIVE</strong></dt>
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<dd>A cursor that can be used to <a href="rsltcurs.htm">scroll in various
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ways</a> through a ResultSet. This type of cursor is insensitive to changes
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made to the database while it is open. It contains rows that satisfy the query
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when the query was processed or when data is fetched.</dd>
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</dl>
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<dl><dt class="dlterm"><strong>TYPE_SCROLL_SENSITIVE</strong></dt>
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<dd>A cursor that can be used to scroll in various ways through a ResultSet.
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This type of cursor is sensitive to changes made to the database while it
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is open. Changes to the database have a direct impact on the ResultSet data.</dd>
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</dl>
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<p>JDBC 1.0 ResultSets are always forward only. Scrollable
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cursors were added in JDBC 2.0.</p>
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<p><strong>Note:</strong> The blocking enabled and
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block size connection properties affect the degree of sensitivity of a TYPE_SCROLL_SENSITIVE
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cursor. Blocking enhances performance by caching data in the JDBC driver layer
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itself.</p>
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<p>See <a href="sensitive.htm">Example: Sensitive and insensitive
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ResultSets</a> that shows the difference between sensitive and insensitive
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ResultSets when rows are inserted into a table.</p>
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<p>See <a href="sensitive2.htm">Example:
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ResultSet sensitivity</a> that shows how a change can affect a where clause
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of an SQL statement based on the sensitivity of the ResultSet.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Concurrency</h4><p>Concurrency determines whether the ResultSet
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can be updated. The types are again defined by constants in the ResultSet
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interface. The available concurrency settings are as follows:</p>
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<dl><dt class="dlterm"><strong>CONCUR_READ_ONLY</strong></dt>
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<dd>A ResultSet that can only be used for reading data out of the database.
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This is the default setting.</dd>
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</dl>
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<dl><dt class="dlterm"><strong>CONCUR_UPDATEABLE</strong></dt>
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<dd>A ResultSet that allows you to make changes to it. These changes can be
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placed into the underlying database. See <a href="rsltchng.htm">Change
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ResultSets</a> for more information.</dd>
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</dl>
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<p>JDBC 1.0 ResultSets are always forward only. Updateable
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ResultSets were added in JDBC 2.0.</p>
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<div class="note"><span class="notetitle">Note:</span> According to the JDBC specification,
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the JDBC driver is allowed to change the ResultSet type of the ResultSet concurrency
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setting if the values cannot be used together. In such cases, the JDBC driver
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places a warning on the Connection object.</div>
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<p>There is one situation
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where the application specifies a TYPE_SCROLL_INSENSITIVE, CONCUR_UPDATEABLE
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ResultSet. Insensitivity is implemented in the database engine by making a
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copy of the data. You are then not allowed to make updates through that copy
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to the underlying database. If you specify this combination, the driver changes
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the sensitivity to TYPE_SCROLL_SENSITIVE and create the warning indicating
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that your request has been changed.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Holdability</h4><p>The holdability characteristic determines
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whether calling commit on the Connection object closes the ResultSet. The
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JDBC API for working with the holdability characteristic is new in version
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3.0. However, the native JDBC driver has provided a connection property for
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several releases that allows you to specify that default for all ResultSets
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created under the connection (see <a href="conprop.htm">Connection properties</a> and <a href="dasrprop.htm">DataSource properties</a>). The API support overrides
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any setting for the connection property. Values for the holdability characteristic
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are defined by ResultSet constants and are as follows:</p>
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<dl><dt class="dlterm"><strong>HOLD_CURSOR_OVER_COMMIT</strong></dt>
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<dd>All open cursors remain open when the commit clause is called. This is
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the native JDBC default value.</dd>
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</dl>
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<dl><dt class="dlterm"><strong>CLOSE_CURSORS_ON_COMMIT</strong></dt>
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<dd>All open cursors are closed when commit clause is called.</dd>
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</dl>
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<div class="note"><span class="notetitle">Note:</span> Calling rollback on a connection always closes all open
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cursors. This is a little known fact, but a common way for databases to handle
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cursors.</div>
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<p>According to the JDBC specification, the default for cursor
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holdability is implementation-defined. Some platforms choose to use CLOSE_CURSORS_ON_COMMIT
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as the default. This does not usually become an issue for most applications,
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but you must be aware of what the driver you are working with does if you
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are working with cursors across commit boundaries. The IBM<sup>®</sup> Toolbox for Java JDBC driver also uses the HOLD_CURSORS_ON_COMMIT
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default, but the JDBC driver for UDB for Windows NT<sup>®</sup> has a default of CLOSE_CURSORS_ON_COMMIT.</p>
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</div>
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<div class="section"><h4 class="sectiontitle">Specify ResultSet characteristics</h4><p>A ResultSet's
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characteristics do not change once the ResultSet object has been created.
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Therefore, the characteristics have be specified before creating the object.
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You can specify these characteristics through overloaded variations of the
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createStatement, prepareStatement, and prepareCall methods.</p>
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<p>See the
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following topics to specify ResultSet characteristics:</p>
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<ul><li><a href="statemnt.htm">Specify ResultSet characteristics</a> for
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Statements</li>
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<li><a href="prepstat.htm">Specify ResultSet characteristics and automatically
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generated key support</a> for PreparedStatement</li>
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<li><a href="callable.htm">Specify ResultSet characteristics and auto-generated
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key support</a> for CallableStatements</li>
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</ul>
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<div class="note"><span class="notetitle">Note:</span> There are ResultSet methods to obtain the ResultSet type and the
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concurrency of the ResultSet, but there is no method to obtain the holdability
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of the ResultSet.</div>
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</div>
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</div>
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<div>
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<ul class="ullinks">
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<li class="ulchildlink"><strong><a href="sensitive.htm">Example: Sensitive and insensitive ResultSets</a></strong><br />
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The following example shows the difference between sensitive and insensitive ResultSets when rows are inserted into a table.</li>
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<li class="ulchildlink"><strong><a href="sensitive2.htm">Example: ResultSet sensitivity</a></strong><br />
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The following example shows how a change can affect a where clause of an SQL statement based on the sensitivity of the ResultSet.</li>
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</ul>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rsltsets.htm" title="The ResultSet interface provides access to the results generated by running queries. Conceptually, data of a ResultSet can be thought of as a table with a specific number of columns and a specific number of rows. By default, the table rows are retrieved in sequence. Within a row, column values can be accessed in any order.">ResultSets</a></div>
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</div>
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<div class="relconcepts"><strong>Related concepts</strong><br />
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<div><a href="rsltcurs.htm" title="The iSeries Java Database Connectivity (JDBC) drivers support scrollable ResultSets. With a scrollable ResultSet, you can process rows of data in any order using a number of cursor-positioning methods.">Cursor movement</a></div>
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<div><a href="rsltdata.htm" title="The ResultSet object provides several methods for obtaining column data for a row. All are of the form get<Type>, where <Type> is a Java data type. Some examples of these methods include getInt, getLong, getString, getTimestamp, and getBlob. Nearly all of these methods take a single parameter that is either the column index within the ResultSet or the column name.">Retrieve ResultSet data</a></div>
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<div><a href="rsltclse.htm" title="To create a ResultSet object, you can use executeQuery methods, or other methods. This article describes options for creating ResultSets.">Create ResultSets</a></div>
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</div>
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<div class="reltasks"><strong>Related tasks</strong><br />
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<div><a href="rsltchng.htm" title="With the iSeries JDBC drivers, you can change ResultSets by performing several tasks.">Change ResultSets</a></div>
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</div>
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<div class="relref"><strong>Related reference</strong><br />
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<div><a href="resultex.htm" title="This is an example of how to use the ResultSet interface.">Example: ResultSet interface for IBM Developer Kit for Java</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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