func (this *Context) EvaluateSubquery(query *algebra.Select, parent value.Value) (value.Value, error) {
subresults := this.getSubresults()
subresult, ok := subresults.get(query)
if ok {
return subresult.(value.Value), nil
}
subplans := this.getSubplans()
subplan, planFound := subplans.get(query)
if !planFound {
var err error
subplan, err = planner.Build(query, this.datastore, this.systemstore, this.namespace, true)
if err != nil {
return nil, err
}
// Cache plan
subplans.set(query, subplan)
}
pipeline, err := Build(subplan.(plan.Operator), this)
if err != nil {
return nil, err
}
// Collect subquery results
collect := NewCollect()
sequence := NewSequence(pipeline, collect)
sequence.RunOnce(this, parent)
// Await completion
ok = true
for ok {
_, ok = <-collect.Output().ItemChannel()
}
results := collect.ValuesOnce()
// Cache results
if !planFound && !query.IsCorrelated() {
subresults.set(query, results)
}
return results, nil
}
