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<com:TContent ID="body">
<h1>Composite Keys or Multiple Complex Parameters Properties</h1>
<p>You might have noticed that in the above examples there is only a single key
being used as specified in the <tt>resultMap</tt> by the <tt>column</tt> attribute.
This would suggest that only a single column can be associated to a related
mapped statement. However, there is an alternate syntax that allows multiple
columns to be passed to the related mapped statement. This comes in handy for
situations where a composite key relationship exists, or even if you simply
want to use a parameter of some name other than <tt>#value#</tt>. The alternate
syntax for the column attribute is simply <tt>param1=column1, param2=column2, ... ,
paramN=columnN</tt>. Consider the example below where the PAYMENT table
is keyed by both Customer ID and Order ID:</p>
<com:TTextHighlighter Language="xml" CssClass="source">
<resultMap id="select-order-result" class="order">
<result property="id" column="ORD_ID"/>
<result property="customerId" column="ORD_CST_ID"/>
...
<result property="payments" column="{itemId=ORD_ID, custId=ORD_CST_ID}"
select="selectOrderPayments"/>
</resultMap>
<statement id="selectOrderPayments" resultMap="select-payment-result">
select * from PAYMENT
where PAY_ORD_ID = #itemId#
and PAY_CST_ID = #custId#
</statement>
</com:TTextHighlighter>
<p>Optionally you can just specify the column names as long as they're in the
same order as the parameters. For example:</p>
<com:TTextHighlighter Language="xml" CssClass="source">
{ORD_ID, ORD_CST_ID}
</com:TTextHighlighter>
<div class="note"><b>Important!</b>
<p>Currently the SQLMap DataMapper framework does not automatically resolve
circular relationships. Be aware of this when implementing parent/child
relationships (trees). An easy work around is to simply define a second result
map for one of the cases that does not load the parent object (or vice versa),
or use a join as described in the "N+1 avoidance" solutions.</p>
</div>
<div class="info"><b class="tip">Info:</b>
Result Map names are always local to the Data Map definition file that they
are defined in. You can refer to a Result Map in another Data Map definition
file by prefixing the name of the Result Map with the namespace of the SqlMap
set in the <tt><sqlMap></tt> root element.
</div>
</com:TContent>
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