Thanks for the response Craig :-) I'm just starting a page for our campus ACM group that will give the possibility of posting articles, forum data, links, etc.
I'm using OJB, but I have to do some odd things to the schema of the database (torque rules!). Issues arise when a table has 5 columns; the 5th is memo-type data which I don't want to select as part of an object most of the time: An example would be: list available articles, and then pull their page content when requested. What I have to do is put that 5th column in its own table to take advantage of lazy loading by OJB (a proxy reference). The other alternative is to create two versions of the bean: ArticleListItem and ArticleItem. ArticleItem extends ArticleListItem, but includes that 5th column. At this point, I would like anyone (even steve b. from tomcat-user) to tell me the recommended course of action in this case. Sorry for the OT Jacob | -----Original Message----- | From: Craig R. McClanahan [mailto:[EMAIL PROTECTED]] | Sent: Wednesday, February 05, 2003 1:10 AM | To: Struts Users Mailing List | Subject: RE: [OT] Which Object Relational mapping tool? | | | | On Tue, 4 Feb 2003, Jacob Hookom wrote: | | > Date: Tue, 4 Feb 2003 23:56:39 -0600 | > From: Jacob Hookom <[EMAIL PROTECTED]> | > Reply-To: Struts Users Mailing List <[EMAIL PROTECTED]> | > To: 'Struts Users Mailing List' <[EMAIL PROTECTED]> | > Subject: RE: [OT] Which Object Relational mapping tool? | > | > In my opinion, this topic is just fine-- it comes up every week :-) | > | > I personally dislike O/R mappers because in most cases, I completely | agree | > that beans and db should be separated, but it's at the point of merger | that | > things get overly complex at the expense of an additional layer that | needs | > just as much configuring as writing your sql code for each use case. | > | | I've had to write some read-only database apps lately -- you know, the | kind where you have 100 or so different SQL SELECT commands to manage, | that often do really complicated joins, and where your business folks keep | tweaking the set of columns to be returned ... and it's just not worth all | the effort to create an O/R mapping for every possible SELECT that you | might ever want to run. | | If you've got tasks like that, the recent nightly builds of Struts 1.1 | (which include commons-beanutils 1.6 or later) contain a secret weapon -- | the org.apache.commons.beanutils.RowSetDynaClass class, which copies the | contents of a java.sql.ResultSet into a set of DynaBeans whose properties | exactly match the columns in your query. This means you can use all the | Struts tags that you know and love to display the results, without ever | having to figure out how to run an O/R mapping tool for every possible | SELECT statement. | | Example code in an Action (assuming you're using JNDI-based data sources | for connection pooling): | | InitialContext ic = new InitialContext(); | DataSource ds = (DataSource) ic.lookup("java:comp/env/jdbc/MyDatabase"); | Connection conn = null; | Statement stmt = null; | ResultSet rs = null; | RowSetDynaClass rsdc = null; | try { | conn = ds.getConnection(); | stmt = conn.createStatement(); | rs = stmt.executeQuery | ("select custid as id, custname as name from customers" + | " where credit_limit > 1000 order by credit_limit descending"); | rsdc = new RowSetDynaClass(rs); | } catch (SQLException e) { | ... deal with exception ... | } finally { | if (rs != null) { | try { | rs.close(); | } catch (SQLException e) { | ; | } | rs = null; | } | if (stmt != null) { | try { | stmt.close(); | } catch (SQLException e) { | ; | } | stmt = null; | } | if (conn != null) { | try { | conn.close(); | } catch (SQLException e) { | ; | } | conn = null; | } | } | | if (rsdc != null) { | request.setAttribute("customers", rsdc.getRows()); | ... forward to the "list customers" page | } | | Example code from the "list customers" page: | | <table> | <tr> | <th>Customer Id</th> | <th>Customer Name</th> | </tr> | <logic:iterate id="customer" name="custoemrs"> | <tr> | <td><bean:write name="customer" property="id"/></td> | <td><bean:write name="customer" property="name"/></td> | </tr> | </logic:iterate> | </table> | | | You will still want to use O-R tools for use cases where you are updating | the contents of a database -- but, for all the selects, you don't really | need to go to all that effort if you don't want to. | | Craig | | PS: There is a performance tradeoff with the approach described above, | because the data is copied into an in-memory array. However, one key | advantage is that you can immediately release the database resources for | the query, so that the ultimate page that renders the output does not have | to worry about it. Most of the no-copy solutions I have seen require you | to deal with closing the result set, and/or releasing the connection back | to the connection pool, in the JSP page itself. To me, that does not seem | like something you really want to make the page author worry about. | | PPS: If you're using JSTL in your pages, the | javax.servlet.jsp.jstl.sql.ResultSupport class can be used in a manner | very similar to what is described above, but makes the query results easy | to access via JSTL tags. That way, you won't be tempted to code the SQL | queries directly in your page, which doesn't really fit into an MVC | paradigm :-). | | | --------------------------------------------------------------------- | To unsubscribe, e-mail: [EMAIL PROTECTED] | For additional commands, e-mail: [EMAIL PROTECTED] --------------------------------------------------------------------- To unsubscribe, e-mail: [EMAIL PROTECTED] For additional commands, e-mail: [EMAIL PROTECTED]
