Looks like you would have to implement some kind of ComparableMap to be
able to use the PairLexicoder (see that the parameterization requires
both types in the Pair to implement Comparable). The Pair lexicoder
requires these Comparable types to align itself with the original goal
of the Lexicoders: provide byte-array serialization for types whose sort
order matches the original object's ordering.
Typically, when we have key to value style data we want to put in
Accumulo, it makes sense to leverage the Column Qualifier and the Value,
instead of serializing everything into one Accumulo Value. Iterators
make it easy to do server-side predicates and transformations. My hunch
is that this is another reason why you don't already see a MapLexicoder
provided.
One technical difficulty you might run into implementing a generalized
MapLexicoder is how you delimit the key and value in one pair and how
you delimit many pairs from each other. Commonly, the "null" byte (\x00)
is used as a separator since it doesn't often appear in user-data. I'm
not sure if some of the other Lexicoders already use this in their
serialization (e.g. the ListLexicoder might, I haven't looked at the
code). Nesting Lexicoders generically might be tricky (although not
impossible) -- thought it was worth mentioning to make sure you thought
about it.
Adam J. Shook wrote:
Hello all,
Any suggestions for using a Map Lexicoder (or implementing one)? I am
currently using a new ListLexicoder(new PairLexicoder(some lexicoder,
some lexicoder), which is working for single maps. However, when one of
the lexicoders in the Pair is itself a Map (and therefore another
ListLexicoder(PairLexicoder)), an exception is being thrown because
ArrayList is not Comparable.
Regards,
--Adam
