Hi Samuel,
 
Yes, you're right, in fact NHibernate is my other preferred tool but I like IBatis flexibility and performance. I just resisted to believe that all the developers using IBatis managed to manually solve the "multiple instances" problem.
 
I heard that there are users asking for some kind of hook into IBatis object instantiation to implement this kind of stateful operation.
 
Thanks for taking the time to answer.
 
Carlos Peix


From: Clough, Samuel (USPC.PRG.Atlanta) [mailto:Samuel_Clough@princetonrg.com]
Sent: Martes, 08 de Mayo de 2007 08:47 a.m.
To: user-cs@ibatis.apache.org
Subject: RE: Kind of architecture question

Not to sound smart or anything, but if you need to ensure that you have only one ref for each logical object, have you considered NHibernate?  iBatis is designed to work in the way it is working.  It allows you to write something very similar to a custom DAO without doing all the heavy lifting.  What you are doing sounds to me like a perfect NHibernate use case.  NHibernate enforces that only one actual reference exists in the session for a specific object.
 
As you've mentioned, you could tweak the iBatis caching but I'm not sure if that's going to give you want you want completely.
 
To me iBatis is perfect for a more high-performance, stateless type of world that I typically work in (although it works in a stateful world as well).  NHibernate is better suited for that more stateful world.  (This is not to say that there aren't crossover areas where you can use either one because there are).


From: Carlos Peix [mailto:peix-listas@praxia.com.ar]
Sent: Tuesday, May 08, 2007 7:31 AM
To: user-cs@ibatis.apache.org
Subject: Kind of architecture question

Hi Shane,
 
I heard the "no access to repository from the domain objects" idea but I can't do that in my daily work, I need to access repository from my domain. Besides that, I use interfaces for all my repositories and I maintain the implementation out of the domain model (reflection or DI is my glue), so I'm OK with that. I just use the service layer to start and commit transactions.
 
Regarding if my main concern is an IBatis issue or not, I was told that IBatis don't want to mess with internal identity maps and I can see why. It need ton control object identity, concurrency, object context, etc.
 
I just want to know how the many programmers that use IBatis cope with that problem.
 
Thanks
 
Carlos


From: Shane Courtrille [mailto:shanecourtrille@gmail.com]
Sent: Lunes, 07 de Mayo de 2007 07:34 p.m.
To: peix-listas@praxia.com.ar
Subject: Re: Kind of architecture question

Hey, Carlos.

Yes, I guess the name for it would be Identity Map.  I have a real concern with having my domain objects call to my repository.  In my world that's the job of my service layer.  To provide the "glue" that brings my domain and technical services together.  But at the same time it would definitely solve this issue. 

I do think I disagree with this not being an iBatis issue.  My understanding is that iBatis is suppose to provide a simple mapping solution that resolves 80% of the work with 20% of the code.  I don't see how you can consider something this simple as not being a very important part of that 80%.  I'm definitely looking forward to a better solution to this problem if anyone can come up with one.

Shane

On 5/7/07, Carlos Peix <peix-listas@praxia.com.ar> wrote:
Hi Shane, thanks for taking the time to answer.
 
Yes, you are talking about an Identity Map I guess, but this solution is harder to implement and tune. It's my last resort though.
 
Of course, definitely the select="CustomerById" needs to be removed. In fact, the command CustomerById uses a different cache that the command CustomerAll so, if we use cache for both commands we can stop IBatis building different instances.
 
One approach I used is for resolving this is implementing the CustomerRepository.GetAll() with an IBatis query (cached) and the CustomerRepository.GetById() resolved in memory. But I'm not very happy with this solution either
 
Of course, the Order ResultMap just get the Customer Id and I resolve the property getter or setter that way.
 
class Order {
 
    // This field is mapped in IBatis
    object customerId;
 
    // this is a transient field
    private Customer customer;
 
    public Customer Customer
    {
        get {
            if ( customer == null )
                customer = CustomerRepository.GetById( customerId );
            return customer;
        }
        set customerId = value.Id; }
    }
 
}
 
Carlos


From: Shane Courtrille [mailto:shanecourtrille@gmail.com]
Sent: Lunes, 07 de Mayo de 2007 07:03 p.m.
To: user-cs@ibatis.apache.org; peix-listas@praxia.com.ar
Subject: Re: Kind of architecture question

I'm just learning iBatis.Net now but I have used the repository <-> mapper pattern in the past.  Usually what I have done is have the repository contain a reference to a cache.  It checks the cache before using the mapping layer to retrieve the item.  The problem I see is your Order select="CustomerById".  Without knowing more about iBatis I would suggest you may need to remove that and instead have your repository fill in the reference after it gets the Order.  Definitely not a solution I'm in love with though.

Shane

On 5/7/07, Carlos Peix <peix-listas@praxia.com.ar> wrote:
Hi all,
 
I used IBatis.NET with success in various projects now but I am still not very happy with my implementations. I'll try to explain my concerns.
 
My environment is .NET 1.1 but I think .NET 2.0 is the same thing. I should say that I try to work guided by the DDD principles, so I access the final store through repositories.
 
I have, for example, an entity Customer (aggregate root or simply a persistent identifiable object) and a CustomerRepository with the following interface:
 
Customer CustomerRepository.GetById( object id );
IList CustomerRepository.GetAll();
...
 
and I also have a Order and OrderRepository with the following interface
 
OrderRepository.GetByNumber( int number );
...
 
The problem I face all the time with IBatis is the I get different instances if I do:
 
// implemented with a Mapper.QueryForObject( "CustomerById", id );
Customer customer1 = CustomerRepository.GetById( object id );
 
// implemented with a Mapper.QueryForList( "CustomerAll" );
Customer customer2 = CustomerRepository.GetAll()[0];
 
// implemented with a Mapper.QueryForObject( "OrderByNumber", number );
// and Customer mapped this way in the OrderResultMap:
//  <result property="customer" column="CustomerId" select="CustomerById" />
Customer customer3 = OrderRepository.GetByNumber( 100 ).Customer;
 
But customer1.Id, customer2.Id and customer3.Id are the same.
 
Ok, this is a situation that need to be controlled, otherwise I could modify or check different instances of the same object. I was told previously that this is not an IBatis problem and I see why (in fact IBatis doesn't know anything about object identity, so it can't control this).
 
The question is: how are you structuring your code to control that situation? there are some "recommended practices"? I started with some ideas (one of them include IBatis cache configuration) but I'm not happy with any of them.
 
Sorry about the long post and thanks in advance.
 
Carlos Peix
 
 



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