Hi,
I have dabbled a bit with both AWS SimpleDB and the sdb library as
well as with the similar Google App Engine Datastore and related
Clojure libraries.
These two parts are indeed no-brainers:
- Support for consistent reads
- Support for literal string queries
Re: numeric formatting
I am not too familiar with the details of numeric types in SimpleDB
and Clojure 1.3. Congruence between the two through usage of longs and
integers sounds good.
Re: type indicators in attribute values
Indeed this gives some troubles when using literal string queries or
using different tools and languages. The suggested move to storing
type indicators in the attribute names instead of values would improve
the usability of
literal string queries and the "LIKE" construct. Below is another
suggestion.
Re: suggestion to be able to customize how the library should
serialize and deserialize values
I have used two clojure libraries with the Google App Engine Datastore
that provide such functionality. Both libraries need an explicit
definition of an entity. They also allow the specification of a
serialization and deserialization function per attribute, for instance
with appengine-clj:
(ds/defentity Link ()
((url :key identity)
(title)
(points)
(date :serialize joda->javadate
:deserialize java->jodadate)))
The two libraries are:
appengine-clj [https://github.com/r0man/appengine-clj/]
clj-gae-datastore [https://github.com/smartrevolution/clj-gae-
datastore]
(Note that the often mentioned appengine-magic has no support for
defining how values should be serialized and deserialized in the
datastore)
To talk in terms of entities is perhaps too much structure for the
simpledb. I would suggest a way to define serialization and
deserialization per attribute per domain in code. This would mean that
there is no encoding of the type of an attribute in its name or value
in the storage. get-attr and put-attr take the domain as an argument,
which can be used to lookup the proper serialization and
deserialization function per attribute.
This approach would do away with storing type information into
simpledb. It is also possible to provide this functionality on top of
the existing simpledb library or the library with the suggested
improvements.
Finally, a (get-attr "domain" "some-id") call returns a {:sdb/id "some-
id"} map when there is no item with that id in the domain. This means
that a get-attr result can always be used a base case to merge updates
in, but I have also found cases where I would have preferred a nil
result when the item doesn't exist. I would prefer the nil returning
case as this works nicely with if-let constructs.
-Gijs
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