Author: wyoung
Date: Thu Jun 28 07:38:44 2007
New Revision: 1632
URL: http://svn.gna.org/viewcvs/mysqlpp?rev=1632&view=rev
Log:
Added store_if() section to userman's tutorial chapter
Modified:
trunk/doc/userman/userman.dbx
Modified: trunk/doc/userman/userman.dbx
URL:
http://svn.gna.org/viewcvs/mysqlpp/trunk/doc/userman/userman.dbx?rev=1632&r1=1631&r2=1632&view=diff
==============================================================================
--- trunk/doc/userman/userman.dbx (original)
+++ trunk/doc/userman/userman.dbx Thu Jun 28 07:38:44 2007
@@ -844,6 +844,31 @@
<sect2>
+ <title>Conditional Result Row Handling</title>
+
+ <para><methodname>Query::store()</methodname> is fine if
+ you really need all the rows the query returns. It sometimes
+ happens that you can't express the full selection criteria
+ in a SQL query. Instead of storing the full result set,
+ then picking over it to find the rows you want to keep,
+ use <methodname>Query::store_if()</methodname>. This is
+ <filename>examples/store_if.cpp</filename>:</para>
+
+ <programlisting><xi:include href="store_if.txt" parse="text"
+ xmlns:xi="http://www.w3.org/2001/XInclude"/></programlisting>
+
+ <para>I doubt anyone really needs to select rows from
+ a table that have a prime number in a given field. This
+ example is meant to be just barely more complex than SQL
+ can manage, to avoid obscuring the point. Point being, the
+ <methodname>Query::store_if()</methodname> call here gives
+ you a container full of results meeting a criterion that you
+ probably can't express in SQL. You will no doubt have much
+ more useful criteria in your own programs.</para>
+ </sect2>
+
+
+ <sect2>
<title>Executing Code for Each Row In a Result Set</title>
<para>SQL is more than just a database query language. Modern
@@ -857,31 +882,27 @@
<programlisting><xi:include href="for_each.txt" parse="text"
xmlns:xi="http://www.w3.org/2001/XInclude"/></programlisting>
- <para>You only need to read the
- <function>main()</function> function to get a
- good idea of what the program does. The key line
- of code passes an SSQLS examplar and a functor
- to <methodname>Query::for_each()</methodname>.
- <methodname>for_each()</methodname> uses the SSQLS
- instance to build a <computeroutput>select
- * from TABLE</computeroutput> query,
- <computeroutput>stock</computeroutput> in this
- case. It runs that query internally, calling
- <classname>gather_stock_stats</classname> on each
- row. This is a pretty contrived example; you could
- actually do this in SQL, but we're trying to prevent
- the complexity of the code from getting in the way
- of the demonstration here.</para>
-
- <para>If you need a more complex query than the
- one <methodname>for_each()</methodname> knows
- how to build, there are two overloads that let
- you use your own query string. One just takes a
- functor and uses the query string held within the
- <classname>Query</classname> object, which you probably
- built up using <classname>Query</classname>'s stream
- interface. The other overload just takes the query
- string directly, along with the functor.</para>
+ <para>You only need to read the <function>main()</function>
+ function to get a good idea of what the program
+ does. The key line of code passes an SSQLS examplar and
+ a functor to <methodname>Query::for_each()</methodname>.
+ <methodname>for_each()</methodname> uses the SSQLS instance to
+ build a <computeroutput>select * from TABLE</computeroutput>
+ query, <computeroutput>stock</computeroutput> in
+ this case. It runs that query internally, calling
+ <classname>gather_stock_stats</classname> on each row. This
+ is a pretty contrived example; you could actually do this in
+ SQL, but we're trying to prevent the complexity of the code
+ from getting in the way of the demonstration here.</para>
+
+ <para>If you need a more complex query than the one
+ <methodname>for_each()</methodname> knows how to build,
+ there are two overloads that let you use your own query
+ string. One just takes a functor and uses the query string
+ held within the <classname>Query</classname> object, which
+ you probably built up using <classname>Query</classname>'s
+ stream interface. The other overload just takes the query
+ string directly, along with the functor.</para>
</sect2>
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