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From Poitras Christian <Christian.Poit...@ircm.qc.ca>
Subject RE: Lazy loading differences between ibatis 2 and 3
Date Wed, 16 Dec 2009 17:09:32 GMT
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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