Hi,
I'll be brief to save you time.
I want to turn my webapplication (for a company I work for, I'm doing a
proof of concept to see if what I want is possible) into a Tapestry5
based system.
Our web applications use multiple databases (to enforce seperation of
concerns and for possible future scaling)
We currently use two filters that provide two EntityManagerFactory
objects (this is just for a small proof of concept webapp) and what I
would like is to have two differently configured Session services.
Obviously, I want to move on, embrace the future and start using a
proper IoC framework.
Now I see in the issue system that this (using multiple databases) is
unsupported. My question concerns a generalized approach. My first
thoughts were on creating some kind of a general Factory service that
would spawn the necessary custom services, but at second thought I found
something that might be less complex.
What if there were a way to copy existing services and override their
configurations? Unless I'm really stupid, this is not yet possible.
One rather obvious issue is that the services I'd like to copy depend on
eachother, so there would have to be a method to map them all to a copy.
Else I would copy a service only to find that it's still depending on
the original's services.
Constraints:
The software is supposed to be unaware of the implementation classes but
it may of course be aware of the externally provided services.
I don't want to copy existing code. Obviously. It would hurt reusability.
Basically, what we're dealing with is a matter of creating different
services (or groups of services) with different configurations.
So, we have 3 services
HibernateSessionManager
HibernateSessionSource
HibernateEntityPackageManager
Session
Now what I would like is to create 3 new services:
ContentSessionManager
ContentSessionSource
ContentEntityPackageManager
ContentSession
ProductsSessionManager
ProductsSessionSource
ProductsEntityPackageManager
ProductsSession
Now I would like a service "ServiceCopier" or something like that to
implement: [pseudocode]
Map<String, String> content = { "Session" => "ContentSession",
"HibernateSessionManager" => "ContentSessionManager",
"HibernateSessionSource"=>"ContentSessionSource",
"HibernateEntityPackageManager"=>"ContentEntityPackageManager" }
Map<String, String> products = {"Session" => "ProductsSession",
"HibernateSessionManager" => "ProductsSessionManager",
"HibernateSessionSource"=>"ProductsSessionSource",
"HibernateEntityPackageManager"=>"PrudctsEntityPackageManager" }
copier.add(first);
copier.add(second);
This would happen in the Module, of course. I would also set
DefaultConfiguration to false and provide my own thingie for that, but
that's simple once the new services are coaxed to use the contributions
using their new service id.
The service builder would construct the three services as normal, except
that whenever ContentSessionManager depends on HibernateSessionSource,
it will depend on ContentSessionSource instead, et cetera. I can then
use @InjectService("ContentSession")
There is one important thing: the contributions from the original
service will have to be included, as well as contributions for the new
service id. If this would not happen, configurers such as
PackageNameHibernateConfigurer.java would not be included. The proper
usage of the concept explained here is that a user would not provide
extra configuration contributions for the base case, but only for the
derived services.
Hmmm this sounds conceptually a bit like namespaces, but you're way
ahead of me in experience so I can't really comment on the similarity.
Anyway, I promised to keep it brief and I doubt I could describe it in
less words. I've described my problem and leave it to you to reply.
Hoping for an answer,
Tom van Dijk.
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