One-sided 1-to-many relationship

[7zark7]

Given doc type A and B:

A has a 1-to-many relationship with B (each A knows of many Bs)
Each B can be known by many As, but does not know which.
A has an array of its known B keys.
A doc:
{
  "_id": "...",
  "kind": "A",
  "b_IDs": ["...", "...", "...", "..."]
}


B doc:
{
  "_id": "...",
  "kind": "B"
}


If I know the key for A, how can I retrieve all related Bs in one view 
or list call?
I'd like to avoid middle-ware that makes sequential calls.

Thanks!