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authorcoreyg <coreyg@13f79535-47bb-0310-9956-ffa450edef68>2014-11-21 09:30:19 +0000
committercoreyg <coreyg@13f79535-47bb-0310-9956-ffa450edef68>2014-11-21 09:30:19 +0000
commit200a40b332420f94992eb39a6d0ea1cf1490ffc4 (patch)
tree1c76ef1d254c7bfc91128a313d319bd60da9d01e /site/trunk/site-publish/rdb-das-cpp-conventionoverconfiguration.html
parent85f53ab6ab4f664d63774c94b672a875c9e52b8a (diff)
Adding tuscany's website to their svn repo for svnpubsub
git-svn-id: http://svn.us.apache.org/repos/asf/tuscany@1640879 13f79535-47bb-0310-9956-ffa450edef68
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+ <H1><A name="RDBDASCPP-ConventionOverConfiguration-ConventionOverConfiguration"></A>ConventionOverConfiguration</H1>
+
+<P>This concept reflects the notion that configuration (defining a bunch of stuff in a side file) can be avoided by following convention (adhering to prescribed patterns) and that this is generally a good thing. The RDB DAS has several reasonable conventions in place and using these can significantly reduce a developer's work-load.</P>
+
+<P>As an example, the RDB DAS provides a straight-forward, one-to-one mapping of database tables to DataObject Types and from table columns to DataObject properties. If a user provides no mapping information to the contrary, a graph of DataObjects returned by the DAS will directly map Types/Properties to the Tables/Columns queried.</P>
+
+<P>For example, consider a database with the following table:</P>
+<DIV class="code panel" style="border-width: 1px;"><DIV class="codeContent panelContent">
+<PRE class="code-java">TABLE CUSTOMER
+ ID INTEGER
+ LASTNAME VARCHAR(20)
+ ADDRESS VARCHAR(30)
+</PRE>
+</DIV></DIV>
+<P>If an application uses the DAS to query this table with the following SQL statement:</P>
+<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent">
+<PRE>SELECT * FROM CUSTOMER
+</PRE>
+</DIV></DIV>
+<P>The DAS will return a graph of DataObjects each of Type CUSTOMER and each instance in will have three properties: (ID, LASTNAME, ADDRESS). Here is the example code. Note that no configuration data is provided at all.</P>
+<DIV class="panel" style="border-width: 1px;"><DIV class="panelContent">
+<P>DASImpl&#42; das = (DASImpl*) DASImpl::getFactory().createDAS(getConnection());<BR>
+ CommandPtr readCustomers = das-&gt;createCommand(&quot;select * from CUSTOMER&quot;);<BR>
+ DataObjectPtr root = readCustomers-&gt;executeQuery();</P>
+
+<P>&nbsp;delete das;</P>
+</DIV></DIV>
+<P>Another piece of convention followed by the RDB DAS has to do with database table keys. When asked to &quot;apply changes&quot;, the RDB DAS scans the SDO ChangeSummery and generates the set of INSERT/UPDATE and DELETE statements needed to flush the graph changes to the database. To generate the correct statements the RDB DAS needs to know how a DataObject's properties map to a database table key. In typical Object/Relational mappings frameworks, this information is provided in a config file with something like this:</P>
+<DIV class="preformatted panel" style="border-width: 1px;"><DIV class="preformattedContent panelContent">
+<PRE>&lt;Table tableName=&quot;COMPANY&quot;&gt;
+ &lt;Column columnName=&quot;ID&quot; primaryKey=&quot;true&quot;/&gt;
+ .
+ .
+ .
+ &lt;/Table&gt;
+</PRE>
+</DIV></DIV>
+<P>However, the RDB DAS understands is that, in the absence of user provided cofiguration data, a DataObject property named &quot;ID&quot; maps to a key column named &quot;ID&quot; in the database. If a developer follows this convention (naming key columns &quot;ID&quot;) then this key-mapping information need not be specified in a configuration file. Convention Over Configuration strings are not case sensitives, so &quot;ID&quot;, &quot;Id&quot;, &quot;iD&quot; or&quot;id&quot; will be mapped as a primary key.</P>
+
+<P>The RDB DAS also has convention in place for mapping DataObject relationships. If a database table (yyy) has a column named xxx_ID then the DAS will assume, in the absence of config data to the contrary, that there is a one-to-many relationship from table xxx to table yyy and that the key column for table xxx is named &quot;ID&quot;.</P>
+
+<P>There is more &quot;convention over configuration&quot; coming. We are currently looking into support for optimistic concurrency control conventions and other areas. </P>
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