Cache null dictionary values by key

[callumbwhyte]

As discussed on #15533 a small performance issue can exist at scale whereby each subsequent call to Umbraco.GetDictionaryValue("...") for non-existent keys results in a database lookup.

This PR implements an option to cache null values in the repository layer, and enables for the DictionaryByKeyRepository repository, following @Migaroez's stellar recommended implementation here.

[github-actions]

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[emmagarland]

Hi @callumbwhyte!

Thanks for your PR to fix #15533, where there is a performance hit if null values need to be looked up in the DB.

One of the Core Collaborators team will review this as soon as possible - and from the issue it seems like one that we'll want HQ to have a glance over too, so we'll contact them about it! (cc @Migaroez)

Best wishes

Emma

[Migaroez]

Code wise this look what we proposed 👍

[mikecp]

Hi @callumbwhyte ,

Thanks for your PR!
I have tested your changes and got some difficulties in getting a "no database access" situation, so I have left some comments on the files. It would be super great if you could have a look at them and let me know what you think 😁
(cc @Migaroez😉)

Cheers!

[madsoulswe]

Any updates/progress on this 😄 this would be super nice to have!

[madsoulswe]

Any chans this is going to make the 13.6 release 😅 @Migaroez

[AndyButland]

I've made some updates to this to resolve the issues raised by @mikecp above. Think I have the logic right now. It wasn't quite as simple as first thought, as I realised if we cache a literally null value, we then can't tell from the cache retrieval if we have found a cached value or not... the value will be null in the case of an existing value that's not yet cached, or a cached null value.

So I've got around this by caching a string to represent null, and then built the logic around that.

It needs a further review of my amends, so if @mikecp, @Migaroez or @callumbwhyte would like to, please do, and hopefully we can get this into 13+.

To test I've added the following to a view and created one dictionary item and not the other:

<div>Value of "Exists": @Umbraco.GetDictionaryValue("Exists")</div>
<div>Value of "DoesNotExist": @Umbraco.GetDictionaryValue("DoesNotExist")</div>

I've confirmed I see the expected value on the front-end. And I've added a debugger to the DefaultCacheRepository.Get() method to step through and verify that we return cached values/make calls to the database as we would expect.

Finally I've populated the DoesNotExist key and verified the cache is invalidated so we see the expected value on the front-end.

[callumbwhyte]

@AndyButland Changes look good to me!

Thanks for picking this up - I've been meaning to come back to this for some time, but time seems to be the exact issue for me lately...!

[AndyButland]

Review and testing steps described in #15576 (comment)

Requested amends have been handled.

[umbracocommunity]

This pull request has been mentioned on Umbraco community forum. There might be relevant details there:

https://forum.umbraco.com/t/usync-imported-translations-get-flat-structure-instead-of-being-nested/1754/3

[KevinJump]

Hi,

Just a heads up, this appears to effect subsequent lookups of dictionary items by their key (the string key, not the guid id). that have been just created, e.g

if an item has just been created then looking for it by this key returns null.

// code to create some dictionary (item) here...
_localizationService.Save(item);

// later in sequence.... 

// lookup
_localizationService.GetDictionaryItemByKey(keyString);

I am not sure how this works on v13.6.0 but not v13.7.0 - and this does look like the only change around that.

[umbracocommunity]

This pull request has been mentioned on Umbraco community forum. There might be relevant details there:

https://forum.umbraco.com/t/dictionary-cache-regression/6041/4