How to pass a parameter from model to a web service?

[AesonErryl]

I am working on this.

In my CONTROLLER JS:

//more codes above
    var isPublic = myAddNewTaskProject.down('[name=chbIsPublic]').getRawValue();


    var record = new App.model.Project.prototype.newRecord(isPublic); //I want to pass the IsPublic value
    record.data.title = projName;
    record.data.description = descrip;


    record.save();
//more codes below

In my Model JS:

Ext.define('App.model.Project', {
  extend: 'Ext.data.Model',
  fields: [
        { name: 'projectid', type: 'string' },
        { name: 'title', type: 'string' },
        { name: 'description', type: 'string' },
        { name: 'ownerPersonid', type: 'string' }
    ],
  proxy: {
    type: 'rest',
    url: 'services/project/'
  },
  newRecord: function (isPublic) { //I don't know what's next.
    var record = App.model.Project.create();
    return record;
  }
});

In my WebService.cs File:

[Post(UriTemplate = "/project/")]
    public SingleResult<Project> SaveProject(Project project, bool isPublic) { //this is where I'll use my isPublic value


      if(isPublic) {
        project.OwnerPersonID = null; //do not assign owner
      } else {
        project.OwnerPersonID = ContextPersonID; //assign an owner of the project
      }


      TimeTrackerController.Save(project);
      return new SingleResult<Project>(project);
    }

I want to pass the value of the 'IsPublic'. But how can I do that inside my Model?