Check if a user has a particular assigned reource object in the client API

Is there a way in the OIM 11.1.1.5 client API (or alternatively old Thor API) to query whether a given user has been assigned a particular resource object (or alternatively to list all assigned resource objects for a user so this can be checked)?  I cannot make out from the API documentation any service/method that seems to do this.
I am using the RequestService to provision users from some import data, but would like to be able to work out whether to initiate a "Provision Resource" request or "Modify Provisioned Resource" request dependent on whether the user already has the associated resource object.