Yes, I did consider that but didn't like the idea of passing the
system around. Also handle-command would need access to the system as
well.
I am wondering whether simply having a 'registry' component which
handlers register themselves with (e.g. a map of {predicate handler})
isn't a way forward and not using defmulti...
On 25 February 2015 at 12:51, Jeroen van Dijk
<[email protected]> wrote:
> So I guess another question is where "handle-command" is being called. What
> about providing the component as argument to the multimethod (there are
> other approaches too depending on your need). So:
>
> (defmulti handle-command(fn [component command] (first command)))
>
> (defmethod handle-command :add-customer [{:keys [db eventstore} [[_
> customer]]]
> ... )
>
> Isn't something like this enough?
>
> Jeroen
>
> On Wed, Feb 25, 2015 at 1:34 PM, Colin Yates <[email protected]> wrote:
>>
>> Hi Jeroen - sure.
>>
>> I have a gateway which can handle a number of 'commands', let's say:
>>
>> AddCustomerCommand
>> ExportQueryCommand
>>
>> to handle the AddCustomerCommand I need access to a database and an
>> eventstore. To handle ExportQueryCommand I need access to the
>> database, a PDF service and so on.
>>
>> One way of achieving this is (assuming commands are of the form
>> [:command-discriminator payload]:
>>
>> (defmulti handle-command first)
>>
>> (defn add-customer [db eventstore customer]
>> ...)
>>
>> (defrecord AddCustomerComponent [db eventstore]
>> ...
>> (start [this] (defmethod handle-command :add-customer [[_ customer]]
>> (add-customer db eventstore customer))..)
>>
>> (defn export-reports [db pdf-generator]
>> ...)
>>
>> (defrecord ExportQueryCommand [db pdf-generator]
>> ...
>> (start [this] (defmethod handle-command :export-query [[_]]
>> (export-query db pdf-generator))..)
>>
>> and so on.
>>
>> Fundamentally my question is one of dispatching where the target of
>> the dispatch requires collaborators that aren't part of the dispatch
>> payload.
>>
>> Does that clarify?
>>
>> On 25 February 2015 at 12:11, Jeroen van Dijk
>> <[email protected]> wrote:
>> > I would try to stay away from any nested def's in components (but also
>> > in
>> > other functions). I'm using component a lot and I never had the need for
>> > this.
>> >
>> > Maybe you can elaborate on why you think you need a multimethod inside
>> > the
>> > component? Maybe a full example?
>> >
>> > Cheers,
>> > Jeroen
>> >
>> >
>> >
>> > On Wed, Feb 25, 2015 at 12:08 PM, Colin Yates <[email protected]>
>> > wrote:
>> >>
>> >> Hi,
>> >>
>> >> I have a number of commands flying around which need to be handled.
>> >> defmulti/defmethod seem a nice answer. The problem is that each command
>> >> handler will need different collaborators (those with long memories
>> >> will
>> >> realise this isn't new ground here ;)).
>> >>
>> >> I want to do something like:
>> >>
>> >> (ns one)
>> >> (defmulti handle first)
>> >>
>> >> (ns two)
>> >> (defrecord CommandAHandler [collab-1 collab-2]
>> >> component/Lifecycle
>> >> (start [this]
>> >> (defmethod handle :command-a ....
>> >> (collab-1 ...)))
>> >>
>> >> I realise that the lifecycle of defmethod doesn't match the component
>> >> (i.e. stopping can't unregister the defmethod), but my main reservation
>> >> is
>> >> that a nested defmethod feels a bit weird. Has anyone done anything
>> >> like
>> >> this before?
>> >>
>> >> Thanks!
>> >>
>> >> --
>> >> You received this message because you are subscribed to the Google
>> >> Groups "Clojure" group.
>> >> To post to this group, send email to [email protected]
>> >> Note that posts from new members are moderated - please be patient with
>> >> your first post.
>> >> To unsubscribe from this group, send email to
>> >> [email protected]
>> >> For more options, visit this group at
>> >> http://groups.google.com/group/clojure?hl=en
>> >> ---
>> >> You received this message because you are subscribed to the Google
>> >> Groups
>> >> "Clojure" group.
>> >> To unsubscribe from this group and stop receiving emails from it, send
>> >> an
>> >> email to [email protected].
>> >> For more options, visit https://groups.google.com/d/optout.
>> >
>> >
>> > --
>> > You received this message because you are subscribed to the Google
>> > Groups "Clojure" group.
>> > To post to this group, send email to [email protected]
>> > Note that posts from new members are moderated - please be patient with
>> > your
>> > first post.
>> > To unsubscribe from this group, send email to
>> > [email protected]
>> > For more options, visit this group at
>> > http://groups.google.com/group/clojure?hl=en
>> > ---
>> > You received this message because you are subscribed to the Google
>> > Groups
>> > "Clojure" group.
>> > To unsubscribe from this group and stop receiving emails from it, send
>> > an
>> > email to [email protected].
>> > For more options, visit https://groups.google.com/d/optout.
>>
>> --
>> You received this message because you are subscribed to the Google
>> Groups "Clojure" group.
>> To post to this group, send email to [email protected]
>> Note that posts from new members are moderated - please be patient with
>> your first post.
>> To unsubscribe from this group, send email to
>> [email protected]
>> For more options, visit this group at
>> http://groups.google.com/group/clojure?hl=en
>> ---
>> You received this message because you are subscribed to the Google Groups
>> "Clojure" group.
>> To unsubscribe from this group and stop receiving emails from it, send an
>> email to [email protected].
>> For more options, visit https://groups.google.com/d/optout.
>
>
> --
> You received this message because you are subscribed to the Google
> Groups "Clojure" group.
> To post to this group, send email to [email protected]
> Note that posts from new members are moderated - please be patient with your
> first post.
> To unsubscribe from this group, send email to
> [email protected]
> For more options, visit this group at
> http://groups.google.com/group/clojure?hl=en
> ---
> You received this message because you are subscribed to the Google Groups
> "Clojure" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> For more options, visit https://groups.google.com/d/optout.
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to [email protected]
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
[email protected]
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
---
You received this message because you are subscribed to the Google Groups
"Clojure" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
For more options, visit https://groups.google.com/d/optout.
