Re: Two step transactions?

I'm against this current version of your proposal because:
1. It's more code than just performing validation in "execute" method
itself (e.g. before modifying the prevalent object).
2. It appears to unnecessarily add an intermediate "validation" object.

A better implementation, in my opinion, although I'm still not sure that
pre-execution validation in Prevayler itself is a good idea, would be:

interface ValidatingTransaction<P>{
    void execute(...
    boolean validate();
}


On 15 November 2013 07:35, Karl Wettin <[email protected]> wrote:

> This is more or less just me thinking out loud, but how would you people
> feel about a transaction that validates fields prior to adding it to the
> journal and executing it?
>
> Why? I'm not quite sure. I just sort of enjoy the idea of separating the
> code that loads objects and throws possible exception from the part that
> actually execute the change on the prevalence.  And I suppose it opens up
> for catching some bad use of transactions and fail faster in business logic.
>
> I was thinking something along the lines of this:
>
>
> interface Validating<P, V> {
>   V prepare(P prevalence)  throws Exception;
> }
>
> interface ValidatingTransaction<P, V> extends Validating<P, V> {
>   void executeOn(P prevalence, Date executionTime, V validation) throws
> Exception;
> }
>
> interface ValidatingTransactionWithQuery<P, R, V>, Validating<P, V> {
>   R executeAndQuery(P prevalence, Date executionTime, V validation) throws
> Exception;
> }
>
> class AddBarToFoo implements ValidatingTransaction<Root, Preparation> {
>
>   static class Preparation {
>     Bar bar;
>     Foo foo;
>   }
>
>   long barIdentity;
>   long fooIdentity;
>
>   Preparation prepare(Root root) throws Exception {
>     Preparation p = new Preparation();
>     p.bar = root.bars.get(barIdentity);
>     if (p.bar == null) throw new NullPointerException("No bar with
> identity " + barIdentity);
>     p.foo = root.foos.get(foodentity);
>     if (p.foo == null) throw new NullPointerException("No foo with
> identity " + barIdentity);
>     return preparation;
>   }
>
>   void executeOn(P prevalence, Date executionTime, Preparation p) throws
> Exception {
>     p.foo.bars.add(bar);
>   }
> }
>
>
> class BusinessLogic {
>   void logic() throws Exception {
>      …
>      try {
>        Service.getInstance().getPrevayler().execute(new
> AddBarToFoo(foo.identity, bar.identity);
>      } catch (PreparationException pe) {
>        // Preparation failed, transaction not appended to the journal
>      } catch (Exception e) {
>        // Execution failed, transaction was appended to the journal
>      }
>   }
> }
>
>
>
>
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