How to fix index error when querying GAE datastore?

Question

When I try to run a query on the datastore ordered by date I get the following error:

NeedIndexError: no matching index found.
The suggested index for this q         


        

Answer 1

Thanks Lawrence, you got me on the right track- I think I have found the answer. The query must EXACTLY match the index definition.

I discovered this by trying different GQL queries in the datastore admin box.

For example, the following 2 queries:

SELECT * FROM Message where ref='' and author='' order by date 
SELECT * FROM Message where ref='' and author='' order by date asc 

both fail with:

no matching index found.

The suggested index for this query is:
- kind: Message
  properties:
  - name: author
  - name: ref
  - name: date

However,

SELECT * FROM Message where ref='' and author='' order by date desc

succeeds. Likewise, queries which have less parameters than the index contains will also fail, eg:

SELECT * FROM Message where ref='' order by date DESC

fails with:

no matching index found.

The suggested index for this query is:
- kind: Message
  properties:
  - name: ref
  - name: date
    direction: desc

So the problem was in my query, the line:

query = query.order(Message.date)

is actually sorting in ascending order, but my index says DESCENDING order. The fix is:

query = query.order(-Message.date)