Mysql::Error error in acts as solr plugin

hi,

      i am using acts_as_solr in plugin, in my table i got three
columns
emp_id, name, experience.
when i tried to run my application i got following error
"Mysql::Error: Unknown column 'employees.id' in 'where clause': SELECT
`employees`.* FROM `employees` WHERE (employees.id in (NULL))"

in my table i dont have column "id", but acts_as_solr search in terms
of ID, is that any way to over come this error by overriding
id to emp_id to make acts_as_solr to search in terms of emp_id like
"employees.emp_id"

thanks,
-pab