[Engine-devel] [engine-devel] frontend builders proposal

[Tomas Jelinek]

Hi Tal,

> I was wondering, for entity such as VM, isn't it better to make a 
> builder for the entity as a whole? Unless you know of a specific parts 
> that are used in smaller units?
well, when you create a new VM or a Template, in both cases you need to build the VM entity from UnitVmModel. 
But, not all the fields which are taken from the UnitVmModel in case of creating the new VM are used also for new Template. 
So, in this case both can use CommonUnitToVmBuilder and QuotaUnitToVmBuilder, but the creating of the VM uses also others (e.g. UsbPolicyUntiToVmBuilder etc)

The situation will be even more complex when the Instance Types and the Images will be introduced which all will be basically VM and UnitVmModel subsets. 
So, they will be able to use some of the common builders but not all and will have some custom.

Tomas

----- Original Message -----
From: "Tal Nisan" <tnisan at redhat.com>
To: "Tomas Jelinek" <tjelinek at redhat.com>
Sent: Monday, January 28, 2013 5:44:31 PM
Subject: Re: [Engine-devel] [engine-devel] frontend builders proposal

Hi Tomas,
I was wondering, for entity such as VM, isn't it better to make a 
builder for the entity as a whole? Unless you know of a specific parts 
that are used in smaller units?

Tal.


On 01/25/2013 11:55 AM, Tomas Jelinek wrote:
> Hi All,
>
> as many of you may know, the way how the frontend and backend models are built on frontend (uicommonweb project) is not really ideal. Currently this logic is copy pasted over and over again to different places where it is needed with minor changes to fulfill the specific requirements. It is not only aesthetically problematic, but I recall tons of bugs caused by introducing a new field and forgetting to add it to every place it is used in GUI.
>
> Now, as there will be big changes in the VM/Template models (http://www.ovirt.org/Features/Instance_Types), so the way how the VM, Template, Pool and also the newly created Instance Types models are being built has to be touched anyhow, it is a great opportunity to rethink the way how we do it.
>
> I have created a simple infrastructure (http://gerrit.ovirt.org/#/c/10874/) which could be used for it, and a PoC patch which uses this infrastructure (http://gerrit.ovirt.org/#/c/11354/). Please note that the PoC is not really impressive in means of removing duplications, I wanted to start with the simplest possibility.
>
> The principles behind the infrastructure:
> - have small, well named, easy to understand and reuse builders
> - this builders can be chained together or embedded to each other to build the full resulting object (composite pattern)
> - this builders can be asynchronous, and the next builder in the chain has to be executed only when the current is completely done
>
> The structure:
> - the base is an interface called Builder which has a method build(source, destination, rest)
> - the builder implementing this interface
>    + will get the source and destination objects
>    + copies whatever he wants from source to destination
>    + when done, executes build on the first element of the rest
>      + this may sound awkward, but this is the way how the async calls can be "linearized" in a general way, not embedding anonymous class into anonymous
>        class into anonymous class... as we do it today.
>      + for synchronous builders, there is a BaseSyncBuilder which takes care of this boilerplate calling of next and exposes a simple method
>        build(S source, D destination)
>    + to simplify the creating and running the chain of builders, there is a BuilderExecutor class (can be created as sync or async)
>
> So, a simple example - even more simple than the PoC patch :)
>
> //create the first builder
> class FirstLetterBuilder extends BaseSyncBuilder<String, StringBuilder>  {
>   @Override
>   protected void build(String source, StringBuilder destination) {
>       // copy the first letter to the destination
>       destination.append(source.charAt(0));
>   }
> }
>
> //create the second builder
> class SecondLetterBuilder extends BaseSyncBuilder<String, StringBuilder>  {
>   @Override
>   protected void build(String source, StringBuilder destination) {
>       // copy the second letter to the destination
>       destination.append(source.charAt(1));
>   }
> }
>
> // usage
> ...
> // create the destination object
> StringBuilder res = new StringBuilder();
>
> // configure the executor with the two builders
> BuilderExecutor<String, StringBuilder>  executor = new BuilderExecutor<String, StringBuilder>(
>          new FirstLetterBuilder(),
>          new SecondLetterBuilder()
>          );
>
> // execute the builder chain ("ab" is the source, res the destination)
> executor.build("ab", res);
>
> // use the result
> ...
>
> That's it. And the nice part is, that this FirstLetterBuilder and SecondLetterBuilder can be reused anywhere or combined with any other builders.
>
> Any comments on this will be more than welcome!
>
> Thank you,
> Tomas
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