Subversion-Projekte lars-tiefland.prado

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<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>

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<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>

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<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}

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<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>&lt;sqlMap&gt;</tt> root element.

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