This is the kind of error I was getting from the dev server:
Dev server error
EventError: could not determine a constructor for the tag '!'
in "<string>", line 38, column 11:
- name: !
^
I tracked this down to a GQL statement like this:
GQL
SELECT * FROM MyEntity WHERE open != true ORDER BY date ASC
The problem was with the != operator. It's not supported!
From the GQL reference...
Python GQL supports operators != and OR. Those operators are not yet supported by Datastore GQL.
Doh! Oh well. That explained some of the problem, but what went wrong, but how to fix it? Well the reason why the DataStore became corrupted was this (source)...
The development web server (dev_appserver.py) automatically adds items to this file when the application tries to execute a query that needs an index that does not have an appropriate entry in the configuration file.
Apparently the dev server doesn't really check what it's indexing, it just blindly tries to create an index. So the index.yaml file in my case got the following entry:
index.yaml
- kind: MyEntity
properties:
- name: !
- name: open
direction: desc
The entry "name: !" is not valid, so the DataStore dies. Fixing it is easy, just remove the invalid name entry, and restart the dev server. Easy!
-i
