Strongly consistent datastore option.

[jongillham]

It might be nice to have a StronglyConsistentDatastore option as with appengine/aetest https://godoc.org/code.google.com/p/appengine-go/appengine/aetest#Options

[mzimmerman]

Sorry for the delay; I'm just seeing this now. Since the production data store does not support this, don't particularly think the development data store should either. If your tests fail on this, do a datastore get on the key first.

[mzimmerman]

See also madelynnblue/goon#41

[jongillham]

I could be wrong but I think the way a datastore.Get on the entity key allows you to query that entity is because datastore.Get takes some time and as a side-effect allows the simulated eventual consistency to catch up. Not because the entity property indexes are updated as a direct result of the datastore.Get – I don't think the datastore works like this.

Therefore the only way to unit test queries is to add a time.Sleep(x) between inserting entities and using datastore.Query which we all know is bad. Hence, why I asked for the StronglyConsistentDatastore param as is provided by the SDK.

Please correct me if I am wrong.

[mzimmerman]

In my limited experience, I've never seen a query fail after the .Get() -- maybe it is a race condition in that the entity is written, but the index isn't necessarily updated. The different thing about the dev datastore is that it creates indexes on the fly if you query them (how index.yaml is generated). In production, you need to load/store an index.yaml file. My assumption then here is that the index is generated/checked on each query in the dev server and since the datastore.Get() ensures that the entity is written, the index generation will find it in the query.

As I've mentioned, doing a datastore.Get() on the entities Key before doing a query has not failed me. Since you're using a time.Sleep() right now, why not change it to a datastore.Get() as suggested? If your tests all pass, then it works as I've seen and described (at least in practice).

[jongillham]

It seems fragile to rely on the quirk that entity property indexes are updated after a datastore.Get in the dev app server datastore. This inconsistency with the production datastore could potentially be removed at any time by the GAE team. Therefore, to me, it seemed nicer to explicitly state in a test that we are switching off eventual consistency with a StronglyConsistentDatastore = true option.

However, I currently use aetest with StronglyConsistentDatastore = true for the specific unit tests that would require time.Sleep and use appenginetesting for integration testing where I want to use modules and only want an eventual consistent datastore for test authenticity.

Feel free to close this as my initial issue was just a suggestion that would allow people to just use appenginetesting without aetest.

[mzimmerman]

Along the same lines, I saw this ticket get updated with a related issue. I think they could be solved in the same way.
https://code.google.com/p/googleappengine/issues/detail?id=10250
In theory, if that all works, then you could use it in production too if you needed that functionality.

I guess the root of my hesitancy to add the feature as you've described is 1) I don't have the itch/time at the moment and 2) I don't think it's wise thing to do since that option doesn't exist in production (you're then testing your development server on a functionally different platform)

I'd take a pull requests for it if you wanted to do it though. It's probably only a handful of lines to implement, but would need tests too.