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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 18:45:05 GMT
Hi Bardamu,

I think it was not clear enough due to the lack of Proxy explanation.
If I have an employee and I call getBoss() on it, it has to load the boss property. But what
if I call a method like this in employee?
public boolean askARase() {
  if (this.getBoss().hasMoney()) {
    return true;
  } else {
    return false;
  }
}

Then, I hope the boss property is loaded before hasMoney() is called on it.
The boss property itself is a proxy that can be defined as <E extends Employee>, but
what is E? Since iBATIS does not know for sure, I has to call the select to get the right
type for boss as soon as any method on Employee is called.

Christian


-----Original Message-----
From: Carlos Pita [mailto:carlosjosepita@gmail.com] 
Sent: Wednesday, December 16, 2009 12:16 PM
To: user-java@ibatis.apache.org
Subject: Re: Lazy loading differences between ibatis 2 and 3

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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