CODEWITHSUNDEEP
google-app-enginegoogle-cloud-datastore
Chobeat
Chobeat

Reputation: 3535

NDB: query on multiple parents given a cursor

I can't understand if this is possible or not.

I need to retrieve all the entities of kind "A", children of a list of entities of kind "B".

So there are multiple children "A" for each entity "B".

This would be easy: i get B-list, the list of entities of kind "B" that i need and for each, i get the list of childrens.

Now, i could sort them after the query, merging them in a single list even if it's not a good practice. My biggest problem is that i don't know how to use a cursor because there are multiple queries.

Then i think i need something that looks like

A.query(ancestor in B-list).fetch(...)

but i can't understand how i can do that or what i should use.

Upvotes: 1

Views: 1373

Answers (1)

Guido van Rossum
Guido van Rossum

Reputation: 16890

You can only specify one query per ancestor. So you'll have to do multiple queries. But if you're a little clever you can do them in parallel. Here's a rough sketch of the code (untested):

futures = []
for b in B_list:
  futures.append(A.query(ancestor=b).fetch_async(...))
results = []
for f in futures:
  results.extend(f.get_result())

Upvotes: 5

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