Trying to query across collections in google Firestore

Question

I am trying to retrieve data from one collection depending on data held in another. If the userUID in my attendance collection equals the userUID in my student collection I would like to retrieve the name of the student. Is this possible?

if you have a document with same userId in attendance and student collection, then you can query student using `WhereEqualTo(fieldName,value)` like `db.collection("student") .whereEqualTo("userId", "idValue").get()` — Mohammed Farhan, Aug 20 '18 at 12:56
can I combine these queries of two collections into one query or how is this possible — , Aug 20 '18 at 13:10
No its not possible to combine queries of two collection into one query. — Mohammed Farhan, Aug 21 '18 at 04:43

score 0 · Answer 1 · answered Aug 20 '18 at 12:56

0

This is currently not possible with Firestore. Firestore queries are limited to a documents in a single collection. You would have to perform multiple gets or queries.

answered Aug 20 '18 at 12:56

Doug Stevenson

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Is there anyway at all to query within a query even to try and retrieve this data and make a connection between the two collections. – Aug 20 '18 at 13:16
As I said, write multiple queries to get the data you need. – Doug Stevenson Aug 20 '18 at 13:20
is there anyway to write a function within a query to retrieve data maybe. – Aug 20 '18 at 13:56
No, you have to perform multiple queries. – Doug Stevenson Aug 20 '18 at 13:58
And to add to this is there any way to write queries within other queries – Aug 20 '18 at 14:22

score 0 · Answer 2 · answered Nov 11 '18 at 01:31

According to multiple Google Firebase engineers, querying across collections is not at all possible, despite the Firestore documentation that says:

If you need to query data across collections, use root-level collections.

https://firebase.google.com/docs/firestore/data-model?authuser=3

I would suggest that Google rewrite this part of their documentation because that sentences literally infers the opposite. It should read along the lines of:

If you need to query data across collections, not happening.

Trying to query across collections in google Firestore

2 Answers2