Model api does not fully work with memory

[PhoenixGrey]

gt, lt such comparisons work fine when the db is configured as mysql, but wrong with memory.

eg,
There is a model called user is generated with age, name, birthday. Using

User.count({age:{gt:10}}, function(err, data) {....})

is fine under compound c but not NODE_ENV="test" compound c, while in config/database.coffee the configuration is set mysql as development env and memory as test env, respectively.