Show cache alias instead of backend repr in calls table

[federicobond]

Description

This changes the values of the backend columns for cache calls in the Cache panel from <django.core.cache.backends.dummy.DummyCache object at 0x1063950a0> to default or the corresponding alias. This makes it much easier to identify which call is made to which backend when several cache backends share the same engine.

Before:

After:

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.

[tim-schilling]

I feel like it's going to be hard for us to remember that this is effectively the old version of initialized_only=True. Do you have any ideas on making this more maintainable? [Specifically if Django changes its implementation upstream.]

The only idea I have is to use a cache._djdt_panel.record = functools.partial(cache._djdt_panel.record, alias=alias)

Though it makes me wonder if we need the panel on the cache at all. Seems like we could just store a _djdt_record function on the cache, where then the partial gets much cleaner.

[federicobond]

Though it makes me wonder if we need the panel on the cache at all. Seems like we could just store a _djdt_record function on the cache, where then the partial gets much cleaner.

We do not need the panel on the cache in the current code, it's just used a monkeypatch marker.

The only idea I have is to use a cache._djdt_panel.record = functools.partial(cache._djdt_panel.record, alias=alias)

I thought about something similar, but it needed more changes to the panel inner workings so I went with the most straightforward implementation to validate interest first. I could try a similar approach, storing a _djdt_record function.

[federicobond]

I came back to rework this but if I understand correctly there is no way to get the alias for the given cache without initializing a connection to the backend as a side effect. Checking for the caches._connections looks like the only way to work around this when monkeypatching existing connections.

[tim-schilling]

Alright thank you @federicobond. We need to document this somehow in the code. I'm between separating it out as it's own function or just commenting the loop here:

def initialized_caches():
    """
    Return the initialized caches and aliases.

    This does the same as`caches.all(initialized_only=True)`, but keeps
    the alias with each cache instance.
    """
    for alias in caches:
        if hasattr(caches._connections, alias):
            yield caches[alias], alias

So the rest can be

for cache, alias in initialized_caches():
    _monkey_patch_cache(caches[alias], alias)
    cache._djdt_panel = self

[tim-schilling]

@federicobond I spotted a few more clean-ups, but this is on the edge of being good to go. Thank you for being patient!