On 09/03/2011, at 4:24 PM, Alan wrote:
> 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.
Well, I don't want the symbols location, name, etc to be evaluated...e.g. I
couldn't use location if not in a macro, right?
Secondly, the structure isn't quite as uniform. Like in the example above
(.. rec (create-query [[location eq "Madrid"] and [name eq "Dhali"]])) should
expand to something like
(.. rec (field "location") (eq "Madrid") and (field "name") (eq "Dhali"))
Maybe I'm still missing something but I can't see how I could do that without a
macro...
Andreas
>
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