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From "Clough, Samuel \(USPC.PRG.Atlanta\)" <Samuel_Clo...@princetonrg.com>
Subject RE: Kind of architecture question
Date Tue, 08 May 2007 11:46:40 GMT
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.


	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. 
	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
		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; }


			From: Shane Courtrille
			Sent: Lunes, 07 de Mayo de 2007 07:03 p.m.
			To: user-cs@ibatis.apache.org;
			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. 
			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 =
				// implemented with a
Mapper.QueryForObject( "OrderByNumber", number );
				// and Customer mapped this way in the
				//  <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
				Carlos Peix 

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