knockout.js partial mapping from json -

on knockout.js site's documentation when data server can this:

// every time data received server: ko.mapping.fromjs(data, viewmodel); 

i'd partially map data object model. possible?

i have viewmodel.jobs[i].jobtype child object, i'd this:

ko.mapping.fromjs(data.jobtype, viewmodel.jobs[i].jobtype); 

... meaning i'd map in jobtype result server specific job's jobtype field.

... keeping in mind:

// not work because viewmodel.jobs[i].jobtype() not function. viewmodel.jobs[i].jobtype(data.jobtype); 

this worked:

ko.mapping.fromjs(data.job, viewmodel.jobs[i]);