how to waitOn data ready using iron-router and publish-composite - meteor

Question

I have the following route :
this.route('groupPage', {
path: '/group/:_groupId',
waitOn: function(){
return Meteor.subscribe("groupPage", this.params._groupId);
},
data: function() {
var group = Groups.findOne({_id: this.params._groupId});
var members = Meteor.users.find({_id : {$in: group.memberIds}}); ******** ISSUE HERE******
return {
group: group,
members: members,
}; }});
and the following publication :
Meteor.publishComposite('groupPage', function(groupId, sortOrder, limit) {
return {
// return the group
find: function() {
if(this.userId){
var selector = {_id: groupId};
var options = {limit: 1};
return Groups.find(selector, options);
}
else{
return ;
}
},
children: [
{ // return the members
find: function(group) {
var selector = {_id: {$in: group.memberIds} };
return Meteor.users.find(selector);
}
}
]}}) ;
Now my issue is that : when the related page renders for the first there is no problems but when i actualize the group Page view the line : var members = Meteor.users.find({_id : {$in: group.memberIds}}); gives me the error : undefined object don't have memberIds property. i guess it's because the subscription is not yet ready when doing group.memberIds , isn't it ? Please a hint.
Thanks.

Answer 1

The data function doesn't wait for the subscription to be ready. Further more, subscriptions in the router are considered an anti-pattern for the most part, and should be done in the template: https://www.discovermeteor.com/blog/template-level-subscriptions/
I would pass to the template the groupId, and then get the group and members in the template, like so:
this.route('groupPage', {
path: '/group/:_groupId',
data: function() {
return {
_groupId: this.params._groupId,
}
}
});
and then in the template file:
Template.groupPage.onCreated(function(){
this.subscribe("groupPage", this.data._groupId);
})
Template.groupPage.helpers({
members(function(){
tempInst = Template.instance()
var group = Groups.findOne({_id: tempInst.data._groupId});
return Meteor.users.find({_id : {$in: group.memberIds}});
})
})

Answer 2

The general pattern of your route and publication are all solid. I suspect it's something simple such as:
There is no group with the _id you're using
You're not logged in when you load the route
Here's a version of your code that guards against the error. Note that the publication executes this.ready() instead of just returning if the user is not logged in.
this.route('groupPage', {
path: '/group/:_groupId',
waitOn: function(){
return Meteor.subscribe("groupPage", this.params._groupId);
},
data: function() {
var group = Groups.findOne({_id: this.params._groupId});
var members = group && Meteor.users.find({_id : {$in: group.memberIds}});
return { group: group, members: members };
}
});
Meteor.publishComposite('groupPage', function(groupId,sortOrder,limit) {
return {
find: function() {
if (this.userId) return Groups.find(groupId);
this.ready()
}
},
children: [
find: function(group) {
var selector = {_id: {$in: group.memberIds} };
return Meteor.users.find(selector);
}
]
});