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From Clinton Begin <clinton.be...@gmail.com>
Subject Re: Lazy loading differences between ibatis 2 and 3
Date Wed, 16 Dec 2009 19:04:52 GMT
Carlos,

We implemented it this way to handle issues with circular
dependencies.  Essentially, yes, all dependencies will be loaded if
you access any of them.

If your getName() getter method accessed the "boss" field internally,
it would fail.

Clinton

On Wed, Dec 16, 2009 at 10:16 AM, Carlos Pita <carlosjosepita@gmail.com> wrote:
> Hi Christian,
>
> I understand your point but I don't get its relation to my question at
> all. Continuing your example, I would ask why employee.getName() will
> prematurely load the boss. A priori, I would expect the proxy to be
> smarter and only trigger the loading of boss if getBoss() was
> effectively called.
>
> Regards
> --
> Bardamu
>
> On Wed, Dec 16, 2009 at 3:09 PM, Poitras Christian
> <Christian.Poitras@ircm.qc.ca> wrote:
>> Hi,
>>
>> The major problem that was present in iBATIS 2 was that lazy loaded class where not
always of the right type.
>> For exemple, if I have multiple subclasses of a class.
>> Person
>> Employee inherits Person
>> Director inherits Employee
>>
>> If I have an object Employee with a method getBoss() that returns an Employee (lazy
loaded), I expect that sometimes it will be a director.
>> In iBATIS 2, testing (employee.getBoss() instanceof Director) will always be false.
This problem is due to the fact that iBATIS does not know the real class of the boss property
and creates a Proxy of Employee.
>> In iBATIS 3, testing (employee.getBoss() instanceof Director) will be true if the
employee's boss is a Director. To know the real type, the statement must be executed.
>>
>> Christian
>>
>>
>> -----Original Message-----
>> From: Carlos Pita [mailto:carlosjosepita@gmail.com]
>> Sent: Wednesday, December 16, 2009 11:45 AM
>> To: user-java@ibatis.apache.org
>> Subject: Lazy loading differences between ibatis 2 and 3
>>
>> Hi all,
>>
>> I've the following sqlmap for ibatis 2. Suppose ibatis has its lazy-loading feature
enabled and I obtain a user U by means of findUserById. Then I call U.getEmail() and findMemberById
is not executed. That's fine, one wouldn't expect the associated member to be loaded until
there is a real need for it. Of course, if then I call
>> U.getMember().getDescription() findMemberById does execute its select, in due time.
That said, for ibatis 3 the same example executes findMemberById as soon as U.getEmail() is
invoked, loading the member before time. That's not surprising if one inspects the code of
ResultObjectProxy (relevant parts copied below). Is this intended to work the way it does
or is it a bug?
>>
>> <sqlMap namespace="User">
>>
>>        <resultMap id="userMap" class="User">
>>        <result property="email" column="email"/>
>>        <result property="member" column="member_id" select="findMemberById"/>
>>        </resultMap>
>>
>>        <resultMap id="memberMap" class="Member">
>>        <result property="description" column="description"/>
>>        </resultMap>
>>
>>        <select id="findUserById" resultMap="userMap">
>>                select * from qpoint_user where id = #id#
>>        </select>
>>
>>        <select id="findMemberById" resultMap="memberMap">
>>                select * from cpp_member where member_id = #id#
>>        </select>
>>
>> </sqlMap>
>>
>>
>> public class ResultObjectProxy {
>>
>>   public Object invoke(Object o, Method method, Object[] args) throws Throwable
{
>>      try {
>>        if (!Object.class.equals(method.getDeclaringClass()) &&
>> PropertyNamer.isGetter(method.getName())) {
>>            lazyLoader.loadAll(); <-- this loads all asociations for every
getter invoked on this proxy
>>        }
>>        return method.invoke(target, args);
>>      } catch (Throwable t) {
>>        throw ExceptionUtil.unwrapThrowable(t);
>>      }
>>    }
>> }
>>
>> Regards
>> --
>> Bardamu
>>
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>>
>>
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>>
>
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