Hi,
Thanks for the detailed reply. Today, I have implemented a similar
example and understood the concept. I've realized that groupBy attribute
take the related key from the "class property", not db table column.
When I've tried the table column as the value of the groupBy, it worked
without any exeptions but with silly results. Every row was mapped with
a category, however there were 9 rows and 3 categories. Isn't it
possible for SQL Mapper to determine if the value of the groupBy really
maps with an existing property?
By the last example everything (ofcourse in the context of groupBy :) )
became more clear.
And one more question. As I see, you prefer to put a product list to
category class, but you do not prefer to put a category reference to
product class. Is this the prefered way to implement this kind of
relationships especially where circular dependencies exist?
Thanks.
-- Ersin
Brandon Goodin wrote:
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
