Andrei Ivanov wrote:
Hi Steve, thanks for answer. So far I am using solution when one have to modify assembly to switch between implementations. As you pointed out, I am using the following approach (let me quote whole picture to make things clear):
assembly.xml
<block class="com.xxx.Main" name="main"> <provide name="block1" role="com.xxx.Service"/> </block>
<block class="com.xxx.DefaultService1" name="block1"> ... </block>
<block class="com.xxx.DefaultService2" name="block2"> ... </block> ------------------------------------------------- Main.xinfo <blockinfo>
<services> <service name="... contract.for.Main..." version="1.0"/> </services>
<dependencies> ... <dependency> <service name="com.xxx.Service" version="1.0"/> </dependency> </dependencies> </blockinfo>
------------------------------------------------- DefaultService1.xinfo
<blockinfo>
<services> <service name="com.xxx.Service" version="1.0"/> </services>
<dependencies> ... </dependencies> </blockinfo> ------------------------------------------------- DefaultService2.xinfo <blockinfo>
<services> <service name="com.xxx.Service" version="1.0"/> </services>
<dependencies> ... </dependencies> </blockinfo> ------------------------------------------------- config.xml <block1>...</block1> <block2>...</block2>
As you pointed, in this case to switch from "block1" to "block2" to be used by "main", one have to simply replace word "block1" with word "block2" in provide clause of "main". So far so good.
Two drawbacks: 1. if there are many blocks which require "com.xxx.Service" to function, one have to replace block1 with block2 in every place in assembly. This is where mistakes can happen
Yep.
2. someone who is implementing new block then must have some idea about how assembly.xml is constructed and this is bad (requires extra documentation and so on).
Yep.
Therefore, it will not be bad if only changes in config will be necessary to add and select new block which provides com.xxx.Service. Then about second approach proposed in your reply:
If you want to do this a composition time, then you would need to
declare "top-block" as dependent on two services (using different
role names) and during your initialization, your implementation
Let me "redraw" above, so that you may point if I am mistaken or not:
top-block: assembly.xml
<block class="com.xxx.Main" name="main"> <provide name="top-block" role="com.xxx.TopBlock"/> </block>
<block class="com.xxx.DefaultTopBlock" name="top-block"> <provide name="block1" role="role1"/> <provide name="block2" role="role2"/> </block>
rest of assembly is the same, is it?
Correct.
------------------------------------------------- Main.xinfo ... <dependency> <service name="com.xxx.TopBlock" version="1.0"/> </dependency>
I think I may stop here since, as I see it already, it will not work. Because there is no way to fetch block1 or block2 inside Main, simply because it's component / service manger will not contain block1 or block2...
Phoenix can establish block1 and block2 and provide these to top-block. The top-block implementation is basically acting as a proxy and directing requests to either block12 or block2 based on the configuration supplied policy. As far as Phoenix is concerning, top-block is a perfectly valid cvandidate for supply the service to Main.
I don't see an issue (but I'm working on other things at the same time and my have just missing simothing important).
Cheers, Steve.
Andrei
----- Original Message ----- From: "Stephen McConnell" <[EMAIL PROTECTED]> To: "Avalon-Phoenix Developers List" <[email protected]> Sent: Wednesday, June 12, 2002 12:59 AM Subject: Re: Doesn't work Re: Using Service / Component Selector in Phoenix
doesn'tAndrei Ivanov wrote:
Hm, after closer look I see that this solution doesn't work.
It just shows how to use other role names (that class name) but it
<[email protected]>tell how to select implementations :-(
If I understand you correctly, you want to be able to select which block implementation is going to provide a service to a dependent block. The routing of the provider to the dependent is declared in the assembly.xml file.
<block class="myDependentBlockClassName" name="top-block" > <provide name="block-b" role="the-role-for-service-A"/> </block>
This is telling Phoenix to use a block you have named as "blockB" as the component provider of service A. To switch between "block-a" and "block-c" is basically a matter of updating the mapping in your assembly.xml.
If you want to do this a composition time, then you would need to declare "top-block" as dependent on two services (using different role names) and during your initialization, your implementation selects which service it is going to use based on the information contained in the configuration.
Hope the helps.
Cheers, Steve.
Andrei
----- Original Message -----
From: "Stephen McConnell" <[EMAIL PROTECTED]>
To: "Avalon-Phoenix Developers List"
theySent: Tuesday, June 11, 2002 4:03 PM Subject: Re: Using Service / Component Selector in Phoenix
The documenthttp://jakarta.apache.org/avalon/phoenix/guide-example-configuration.html
contains a description of how to handle this inside Phoinix.
Cheers, Steve.
Andrei Ivanov wrote:
Hi, I came across with simple problem (I think it is simple for experienced Avalon developers) with my Phoenix-based application.
The problem is as follows: I have phoenix service which contract is defined in interface
A. ServiceInterface
I have two different block which offer service A (in other words
different
implementation for the same service):
Blocks B. offers A C. offers A
B and C should be configured and initialized differently as well as
thoughwill depend on different services.
I would like to be able to specify which block will be used (B or C) to provide service A changing only configuration (config.xml) file. Can anyone give me example how to achieve that and what is the standard practice for Phoenix-based application for this?
Regards, Andrei
----- Original Message ----- From: "Peter Royal" <[EMAIL PROTECTED]> To: "Avalon-Phoenix Developers List"
<[email protected]>
Sent: Monday, June 10, 2002 5:44 PM Subject: Re: Constraints on dependencies
On Thursday 06 June 2002 07:43 pm, Peter Donald wrote:
1. Sometimes. I haven't seen any container-specific examples yet1. Are constraints container specific or not? 2. Is there a subset of constraints that are container agnostic? 3. How do we represent constraints in the system? An opaque string? A Configuration tree? An XPath expression? 4. Do the providers or the Kernel validate the constraints? 5. Do the providers get informed that they must conform to certain constraints? 6. Does validation occur at initialization time or assembly time?
My answers would be;
likely
;)
2. Yes. Mainly anything that involves lookup( ROLE ), ie. component
assembly
3. XPath or other evaluated expression :) 4. Kernel 5. No, but there may be cases where they need to be queried by the
kernel
for
constraint resolution (like the ORB example. the kernel will most
<mailto:[EMAIL PROTECTED]>
be
unaware that its ORB component hosts others) 6. Both. As much as possible should be done at assembly, but I'm sure
some
must be defered to init time.
The problem is basically that in some cases it is going to be
practically
impossible for kernel to validate the constraint unless the provider conforms to very specific contracts or is self validating.
I agree. I'd opt more for the "specific contracts" option, which could
be
as
easy as exposing MetaInfo classes. -pete
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