code: function (m1, m2, fship) {
      var query = {_id: m1};
      query[pathName] = {$elemMatch: {_id: m2}};
  
      var updater = {$set: {}};
      updater.$set[pathName+".$.status"] = fship.status;
  
      return _update(query, updater, fship);
    }
docs: Return a function to update a friendship between two parties
  
  @api private