On Mar 8, 9:14 pm, Andreas Kostler <andreas.koestler.le...@gmail.com>
wrote:
> Hi Daniel,
> Thanks for your reply.
> On 09/03/2011, at 11:57 AM, Daniel Solano Gomez wrote:
> > On Wed Mar 9 11:16 2011, Andreas Kostler wrote:
> >> Hi all,
>
> >> I need a macro to basically outputs this:
>
> >> (macroexpand '(chain-field-queries record "location" "name" "country"))
> >> (. (. (. record (field "location")) (field "name")) (field "country"))
>
> >> Which chains method calls on a java object. e.g.
> >> record.field("location").field("name").field("country"). etc...
> >> so far so good. I though I could modify the .. macro for this:
>
> >> (defmacro chain-field-queries
> >> ([x form] `(. ~x (field ~form)))
> >> ([x form & more] `(chain (. ~x (field ~form)) ~@more)))
>
> >> However, this results in
> >> (macroexpand '(chain-field-queries record "location" "name" "country"))
> >> (. (. (. record (user/field "location")) (user/field "name")) (user/field
> >> "country"))
>
> > You could quote the field as a symbol:
>
> > (defmacro chain-field-queries
> > ([x form] `(. ~x (~'field ~form)))
> > ([x form & more] `(chain-field-queries (. ~x (~'field ~form)) ~@more)))
>
> Yes, I don't know why I wasn't thinking of doing that...
>
> > Is a macro really required? You can do this as a function:
>
> I think it is required. I'm trying to compose a query of the form
>
> (defn make-native-query [db str foo]
> (. (proxy [ONativeSynchQuery]
> [db str foo]
> (filter [rec]
> (.. rec (field "location") (eq "Madrid") go))) run
> objs))
>
> Unfortunately, I'm bound to this style of query composition by the java api
> I'm working with. So ideally, I'd like to be able to do something like
>
> (select (where [[location eq "Madrid"]
> and [name eq "Dhali"]])
>
> And this would expand to
>
> (defn make-native-query [db str foo]
> (. (proxy [ONativeSynchQuery]
> [db str foo]
> (filter [rec]
> (.. rec (field "location") (eq "Madrid") and (field
> "name") (eq "Dhali") go))) run objs))
>
> So, technically, I want something along the lines
>
> (defn make-native-query [db str foo]
> (. (proxy [ONativeSynchQuery]
> [db str foo]
> (filter [rec]
> (.. rec (create-query [[location eq "Madrid"]
> and
> [name eq
> "Dhali"]]) go))) run objs))
>
> However, this doesn't seem to be possible. dot-dot doesn't evaluate the
> create-query macro.
> I must be missing something. If anyone could point me in the right direction
> :)
>
> Andreas
>
>
>
>
>
>
>
> > (defn chain-field-queries
> > [record & fields]
> > (let [query (fn [r f] (. r (field f)))]
> > (reduce query record fields)))
>
> > Sincerely,
>
> > Daniel Solano Gómez
You seem to be missing Daniel's point. There's no reason you need to
expand into exactly (.. foo (field "test") (field "more")); you could
just as well expand into (let [data1 foo, data2 (.field data1 "test"),
data3 (.field data2 "more")] data3), which is basically what the ..
shorthand expands to eventually.
And because the latter result is exactly the sort of thing reduce is
good at, you don't need a macro at all.
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