Re-initialize template with new id on selectbox change - meteor

Question

I have a selectbox in template A which selects an item "name and id".
I also have an "item" template that needs an ID as parameter to load its data from its database. I am using a session variable for the id and I pass the id to the "item" template using return Session.get . This only works for on load. When the session variable change the "item" template is not updated. How do I get the "item" template to re-initialize
Some code:
Template.selectBox.helpers({
selectList: function () {
return Templates.find({}, {fields: {'_id': 1, 'name': 1}});
},
selectedId: function() {
return Session.get("selectedId");
}
});
Template.selectBox.events({
'change #item-chooser': function (event) {
var selectedId = $(event.currentTarget).find(":selected").val();
if (typeof(selectedId) === 'undefined'
|| selectedId === "new") {
Session.set("selectedId", "new");
}
else {
Session.set("selectedId", selectedId);
}
}
});
The items template is called using
{{> item selectedId}}
Template.item.onCreated(function() {
var selectedId = this.data.selectedId;
this.selectedItem = new ReactiveVar;
if (typeof(selectedId) === 'undefined'
|| selectedId === "new") {
this.selectedItem.set(emptyItem);
}
else {
var selectedItemData = Templates.findOne({_id: selectedId});
this.selectedItem.set(selectedItemData );
}
});

Answer 1

It's important to note that the Template.onCreated method is not reactive so if you have reactive variables, this method does not automatically re-run when a reactive data source changes unlike Template.helpers
The easiest way to fix your problem would be to use autorun
Template.item.onCreated(function(){
var self = this;
self.autorun(function(){
// some code that has a reactive data source (e.g. Session Var, Collection, or Reactive Var
// NOTE: you can access template instance data using self.data
});
});
However, based on your description, I think there could be a better way to handle your problem using Template.helpers
Template.item.helpers({
selectedItem: function(){
return Templates.findOne({_id: Session.get("selectedId")});
}
});