Subversion-Projekte lars-tiefland.prado

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<h1>Implicit Result Maps</h1>

<p>If the columns returned by a SQL statement match the result object, you may

not need an explicit Result Map. If you have control over the relational

schema, you might be able to name the columns so they also work as property

names. In the following example, the column names and property names

already match, so a result map is not needed.</p>

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<statement id="selectProduct" resultClass="Product">

  select

    id,

    description

  from PRODUCT

  where id = #value#

</statement>

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<p>Another way to skip a result map is to use column aliasing to make the column

names match the properties names, as shown in the following example.</p>

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<statement id="selectProduct" resultClass="Product">

  select

  PRD_ID as id,

  PRD_DESCRIPTION as description

  from PRODUCT

  where PRD_ID = #value#

</statement>

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<p>Of course, these techniques will not work if you need to specify a column

type, a null value, or any other property attributes.</p>

<h1>Primitive Results (i.e. String, Integer, Boolean)</h1>

<p>Many times, we don't need to return an object with multiple properties. We

just need a string, integer, boolean, and so forth. If you don't need to

populate an object, SQLMap can return one of the primitive types instead. If

you just need the value, you can use a primitive type as a result class, as

shown in following example.</p>

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<select id="selectProductCount" resultClass="integer">

  select count(1)

  from PRODUCT

</select>

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<resultMap id="select-product-result" resultClass="string">

  <result property="value" column="PRD_DESCRIPTION"/>

</resultMap>

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<h1>Maps with ResultMaps</h1>

<p>Instead of a rich object, sometimes all you might need is a simple key/value

list of the data, where each property is an entry on the list. If so, Result

Maps can populate an array instance as easily as property objects. The syntax

for using an array is identical to the rich object syntax. As shown in following example,

only the result object changes.</p>

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<resultMap id="select-product-result" class="array">

  <result property="id" column="PRD_ID"/>

  <result property="code" column="PRD_CODE"/>

  <result property="description" column="PRD_DESCRIPTION"/>

  <result property="suggestedPrice" column="PRD_SUGGESTED_PRICE"/>

</resultMap>

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<p>In the above example, an array instance would be created for each row

in the result set and populated with the Product data. The property name

attributes, like <tt>id</tt>, <tt>code</tt>, and so forth, would be the key of the

entry, and the value of the mapped columns would be the value of the entry.</p>

<p>As shown in the following example, you can also use an implicit Result

Map with an array type.</p>

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<statement id="selectProductCount" resultClass="array">

  select * from PRODUCT

</statement>

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<p>What set of entries is returned by the above example depends on what

columns are in the result set. If the set of column changes (because columns

are added or removed), the new set of entries would automatically be returned.</p>

<div class="note"><b class="tip">Note:</b>

Certain providers may return column names in upper case or lower case format.

When accessing values with such a provider, you will have to pass the key name

in the expected case.

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