Rally API 2 query historical velocity - rally

Question

I am doing some processing across iterations in a release and I want to find out what the teams velocity was at that point in time, is there any way to use the lookback API or otherwise get the information for that period?
i.e. the Rally generated velocity at that time or manually calculate the last 10 or all time velocity measures?
So, based on the responses below I have ended up with this code:
_getVelocity: function() {
this.logger.log("_getVelocity");
var me = this;
var deferred = Ext.create('Deft.Deferred');
Ext.Array.each(this.iterations,function(iteration){
iteration.PlanEstimate = 1;
me.logger.log("Fetching velocity for iteration", iteration.Name);
var start_date_iso = Rally.util.DateTime.toIsoString(iteration.StartDate);
var end_date_iso = Rally.util.DateTime.toIsoString(iteration.EndDate);
var type_filter = Ext.create('Rally.data.lookback.QueryFilter', {
property: '_TypeHierarchy',
operator: 'in',
value: this.show_types
});
var date_filter = Ext.create('Rally.data.lookback.QueryFilter', {
property: '_ValidFrom',
operator: '>=',
value:start_date_iso
}).and(Ext.create('Rally.data.lookback.QueryFilter', {
property: '_ValidFrom',
operator: '<=',
value:end_date_iso
}));
var filters = type_filter.and(date_filter);
me.logger.log("Filter ", filters.toObject());
Ext.create('Rally.data.lookback.SnapshotStore',{
autoLoad: true,
filters: filters,
fetch: ['FormattedID','PlanEstimate','ScheduleState'],
hydrate: ['ScheduleState'],
listeners: {
scope: this,
load: function(store,it_snaps,successful) {
if ( !successful ) {
deferred.reject("There was a problem retrieving changes");
} else {
me.logger.log(" Back for ", it_snaps.length, it_snaps);
deferred.resolve(it_snaps);
}
}
}
});
});
deferred.resolve([]);
return deferred;
},
The shape of this code and the filters etc is lifted from another function in the same app that IS working, however this one is NOT working, I get the following errors:
Uncaught TypeError: Cannot read property 'Errors' of null
GET https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/99052282…ScheduleState%22%5D&pagesize=20000&start=0&jsonp=Ext.data.JsonP.callback49 400 (Bad Request)

Answer 1

Since LookbackAPI gives historic data, you may query stories at the specific point of time and get number of points completed at that time. There is no Rally generated velocity, so this has to be accessed and summed up manually. For example, I have iteration that started on August 7 and ended on August 14, but if I want data from August 10 I use:
https://rally1.rallydev.com/analytics/v2.0/service/rally/workspace/1234/artifact/snapshot/query.js?find={"Iteration":5678,"_TypeHierarchy":"HierarchicalRequirement",_ValidFrom:{$gte:"014-08-10",$lte:"2014-08-14"}}&fields=['FormattedID','ScheduleState','PlanEstimate']&hydrate=['ScheduleState']
UPDATE: As far as the code you posted, change
var start_date_iso = Rally.util.DateTime.toIsoString(iteration.StartDate)
var end_date_iso = Rally.util.DateTime.toIsoString(iteration.EndDate);
to
var start_date_iso = Rally.util.DateTime.toIsoString(iteration.get('StartDate'),true);
var end_date_iso = Rally.util.DateTime.toIsoString(iteration.get('EndDate'),true);
I replicated the bad request error with your syntax, and after changing it to this format it worked: iteration.get('StartDate'),true
App source code is in this repo.