Reusing a resultMap for different column names

Question

Is there a way of reusing the same resultMap multiple times in a single query.

For example, suppose I have a "foo" resultMap:

<resultMap id="foo" class="Foo">
  <result property="Bar" column="bar" />
</resultMap>

Is there a way to define another resultMap that reuses the above for different columns? Something like...

<resultMap id="fizz"class="Fizz">
  <result property="Foo1" column="bar=bar1" resultMapping="foo" />
  <result property="Foo2" column="bar=bar2" resultMapping="foo" />
  <result property="Foo3" column="bar=bar3" resultMapping="foo" />
</resultMap>

Answer 1

Almost. If you select the ID of the Foo in your query, you can have the Fizz result map execute a SELECT for that ID, which will use the Foo result map.

<result property="Foo1" column="bar1Id" select="selectFoo"/>

(Assuming you have a selectFoo query defined.) But that's extremely slow with large result sets, since it does an additional SELECT for every row.

iBATIS has a solution to this problem for the typical case, where you have a composite object that contains various other objects. First, you define a query that joins your tables, then you can use fooMap to populate a Foo:

<result property="Foo1" resultMap="fooMap"/>

But you can't use that result map twice for two different Foos because the result map specifies certain column names. You can use another technique, though:

<result property="foo1.bar" column="foo1bar"/>
<result property="foo2.bar" column="foo2bar"/>

More detail in page 35 of the iBatis Datamapper manual.

Answer 2

you could use resultmaps, which extend another resultmap e.g.

<resultMap id="document" class="Document"> 
  <result property="Id" column="Document_ID"/>
  <result property="Title" column="Document_Title"/>
  <discriminator column="Document_Type" type="string"/>
  <subMap value="Book" resultMapping="book"/>
  <subMap value="Newspaper" resultMapping="newspaper"/>
</resultMap>

<resultMap id="book" class="Book" extends="document"> 
  <property="PageNumber" column="Document_PageNumber"/>
</resultMap>

more info: http://ibatis.apache.org/docs/dotnet/datamapper/ch03s05.html