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Dave Tenny wrote:
> If I do something like a describe-instances call in amazonica, I get
> a typical clojure-y set of data fairly deeply nested data structures
> that I have yet to master with respect to traversing using basic
> clojure operations.
>
> Given a result that basically ends up looking like pages of
> interleaved maps and arrays, what should I be using to pick out
> nested key/value information?
>
Hi Dave,
You want to look at extending the IMarshall protocol -- it defines how
the java objects returned by the API are (de?)-serialized into Clojure
datastructures. You can flatten the results massively without much work.
Check the docs, but the examples in the source code are better (as
below). Look at how it's done for some of the API, e.g. S3:
(extend-protocol IMarshall
S3Object
(marshall [obj]
{:bucket-name (.getBucketName obj)
:key (.getKey obj)
:input-stream (.getObjectContent obj)
:object-content (.getObjectContent obj)
:redirect-location (.getRedirectLocation obj)
:object-metadata (marshall
(.getObjectMetadata obj))}))
Note that you can also nest calls recursively if you have to (e.g. some
objects are inexplicably tied to one another -- .getResourceRecordSet
comes to mind). Most calls are just chains of reflection, IIRC, so
indeed there are likely pages of arbitrary nesting.
You're also going to want the amazon java api docs handy in order to
figure out which methods you'll want for which objects you come across.
The REPL & a good autocomplete is invaluable here too.
Cheers,
- ----
Sam Halicke
@samhalicke
> {:reservations [{:reservation-id "r-3da23a55", ... pages of output
> ... }]}]}]} user=>
>
> 'get-in' won't do it because of the arrays (or PersistentArrayMaps,
> as the case may be). I was hoping to avoid zippers, but maybe that is
> the idiomatic way to do it, I don't know.
>
> What's the easy way to traverse these things? This is a very common
> data pattern in using clojure to access everything from html content
> to AWS data. I just want to pluck out the :instance k/v information
> in the nested morass of data printed at my REPL but I haven't yet
> found the intuitive and idiomatic way to do it.
>
Yeah, skip traversal and just get the information you want in as flat of
a data structure as you want using the marshalling/coercion bits.
>
>
>
>
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