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From Tim.Ham...@mcnichols.com
Subject Re: Problem with several one to many relationships in breadth
Date Mon, 19 Feb 2007 15:47:17 GMT
Hi Jeff,

I'm very confused.  Our application has many examples of  independent 
lists as in Claudio's example.  This worked until we implemented release 
2.3.  We then backed up to 2.2 with the same result and then regressed 
back to 2.1.7.597 which does indeed work.  We will have much work to do in 
order to change to nested selects for the many cases where we used this 
feature.  There must be some code differences related to this area from 
2.1.7.597 to 2.2.0.638.

Tim Hammar







"Jeff Butler" <jeffgbutler@gmail.com> 
02/19/2007 10:36 AM
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Re: Problem with several one to many relationships in breadth






iBATIS groupBy support does not support two independant lists.  This would 
be a very difficult problem to solve and would require us to deal with 
object identity - which we don't deal with now.
 
So with groupBy, you can have one and only one list that is automatically 
populated.  Other lists will need to be populated with a nested select.
 
Jeff Butler


 
On 2/19/07, Tim.Hammar@mcnichols.com < Tim.Hammar@mcnichols.com > wrote: 

Greetings Claudio, 

We too have this problem with the latest two releases.  If you use version 
2.1.7.597 you should have no problems - hopefully you have not implemented 
any new features like we had (and had to scramble to undo).  Versions 2.2 
and 2.3 will not handle what you are trying to do.  I have been so swamped 
that I have been unable to generate a test case and submit a bug report. 
Maybe your example will suffice. 

Regards, 
Tim Hammar 




"Claudio Iacovozzi" <claudio.iacovozzi@googlemail.com > 
02/19/2007 06:51 AM 

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Problem with several one to many relationships in breadth









We have a problem filling objects with several '1 to many
relationships' in breadth from one single SQL statement.

On page 40 of the iBatis Data Mapper Developer Guide the 'groupBy' 
construct is described as follows:
"Using this approach, you can solve any N+1 problem of any depth or 
breadth."

This just seems to work for any depth but NOT for any *breadth*.

Example:

An insurance agent contains a list of customers as well as a list of
insured events.

<resultMap class="agent" id="agent" groupBy="id" >
<result property="id" column="agentId" /> 
 <result property="firstName" column="agent_firstname" />
 <result property="lastName" column="agent_lastname" />
 <result property="events" resultMap="event" /> 
 <result property="customers" resultMap="customer" />
</resultMap>

<resultMap class="event" id="event" groupBy="id" >
 <result property="id" column="eventId" /> 
 <result property="title" column="title" />
</resultMap>

<resultMap class="customer" id="customer" groupBy="id" >
<result property="id" column="customerId" /> 
 <result property="firstName" column="customer_firstname" />
 <result property="lastName" column="customer_lastname" />
 <result property="street" column="street" /> 
 <result property="city" column="city" />
</resultMap>

- The used SQL statement:

<select id="getAgent" resultMap="agent" parameterClass="int"> 
SELECT a.agentId, a.FirstName as agent_firstname, a.LastName as
agent_lastname, b.eventId, b.title,
c.customerId, c.FirstName as customer_firstname, c.LastName as
customer_lastname, c.street, c.city

FROM insurance_agent a, agenteventlink ab, insured_event b, customer c 
WHERE a.agentId = ab.agentId
AND ab.eventId = b.eventId
AND b.customerId = c.customerId
AND a.agentId = #id#

ORDER BY a.agentId,  c.customerId
</select>

- The returned result set:
agentId,agent_firstname,agent_lastname,eventId,title,customerId,customer_firstname,customer_lastname



{1,Agent1,Smith,1,housebreaking,1,Customer1,Johnson}
{1,Agent1,Smith,4,theft,1,Customer1,Johnson}
{1,Agent1,Smith,2,damage,3,Customer2,Miller}


What we would like to achieve is getting a bean of type Agent, which 
contains two lists of all its customers and all its associated
insured events:

Agent1  --> List<Customer> {1:Customer1, 3:Customer2}
            --> List<Event> {1:housebreaking, 2:damage, 4:theft} 
 

But iBatis creates a bean like this:
Agent1  --> List<Customer> {1: Customer1, 1:Customer1, 3: Customer2}
           --> List<Event> {1:housebreaking, 2:damage, 4:theft} 


We want to avoid several SQL statements to get the necessary data (one
to get all events, and one to get all customers).

Any solution ?



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