The real issue that is addressed with the groupBy is the ability to
use a single query for populating complex properties mapped in the
resultMap with the <result...resultMap="..."/> tag. In the past you
would be required to map to a statement with the select attribute of
the result tag which meant multiple additional queries and redundant
object population. There were other strategies that were just as
inneficient. The groupBy eliminates this by allowing you to specify
the repeating property that will identify this object and populate the
class defined in the resultMap. Further you can chain multiple
resultMaps using the <result...resultMap="..."/> tag and map any
number of objects with groupBy using the same select results.
Following is a sample Clinton posted from the unit tests a while back.
It may help you to understand groupBy better:
<resultMap id="categoryResult" class="testdomain.Category"
groupBy="categoryId">
<result property="categoryId" column="catid"/>
<result property="name" column="name"/>
<result property="description" column="descn"/>
<result property="productList" resultMap="productResult"/>
</resultMap>
<resultMap id="productResult" class="testdomain.Product" groupBy="productId">
<result property="productId" column="productid"/>
<result property="categoryId" column="category"/>
<result property="name" column="name"/>
<result property="description" column="descn"/>
<result property="itemList" resultMap="itemResult"/>
</resultMap>
<resultMap id="itemResult" class="testdomain.Item">
<result property="itemId" column="itemid"/>
<result property="productId" column="productid"/>
<result property="listPrice" column="listprice"/>
<result property="unitCost" column="unitcost"/>
<result property="supplierId" column="supplier"/>
<result property="status" column="status"/>
<result property="attribute1" column="attr1"/>
<result property="quantity" column="qty"/>
</resultMap>
<select id="getAllCategories" resultMap="categoryResult" >
select *
from category c, product p, item i, inventory v
where c.catid = p.category
and p.productid = i.productid
and i.itemid = v.itemid
</select>
<select id="getFish" resultMap="categoryResult" >
select *
from category c, product p, item i, inventory v
where c.catid = p.category
and p.productid = i.productid
and i.itemid = v.itemid
and c.catid = 'FISH'
</select>
On 6/8/05, Ersin Er <[EMAIL PROTECTED]> wrote:
> Brandon Goodin wrote:
>
> >This will help you:
> >http://opensource.atlassian.com/confluence/oss/display/IBATIS/How+do+I+get+around+the+N+Plus+1+selects+problem%3F
> >
> >
> Infact, the document is the same as the Developer's Guide. What a pity,
> it did not help me. Anyway, I'm trying and learning myself.
>
> The groupBy attribute's value is a class property, not a table column,
> right?
>
> >On 6/6/05, Ersin Er <[EMAIL PROTECTED]> wrote:
> >
> >
> >>Hi,
> >>
> >>What is the porpose of "groupBy" attribute used in the SQL Mapper doc for
> >>"Complex Collection Properties" subject? It says "The important items here
> >>are the groupBy="quarter" attribute.." but it doesn't say why. I've tried
> >>my own example for 1:M relations and I did not the effect of groupBy
> >>attribute clearly. (After a few examples, a new sample doc will come.. :)
> >>)
> >>
> >>Thanks.
> >>
> >>--
> >>Ersin
> >>
> >>
> >>
>
>
>
