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From Ersin Er <ersin...@cs.hacettepe.edu.tr>
Subject Re: groupBy
Date Wed, 08 Jun 2005 21:39:37 GMT
The main problem with the developer guide for Complex List Properties 
section was

1) The example uses groupBy attribute value as the table column name 
which is same as class property. I thought its value comes from table 
column. It the table column's and class property's names were different 
it would be much more easier to understand.
2) The example query was also a groupBy query. So I thought that groupBy 
attribute in the mapping xml has some relation with the query itself.

I think these are important points that makes the document hard to 
understand for a newbea.

Cheers,
Ersin

Ersin Er wrote:

> 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 <ersin.er@cs.hacettepe.edu.tr> 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 <ersin.er@cs.hacettepe.edu.tr> 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
>>>>>
>>>>>
>>>>>
>>>>>       
>>>>
>>>
>>>   
>>
>



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