fix IntegrityErrors occuring when creating ResolutionNoteSlackMessage objects

[joeyorlando]

What this PR does

Which issue(s) this PR fixes

Closes https://github.com/grafana/oncall-private/issues/1822

Checklist

• Unit, integration, and e2e (if applicable) tests updated
• Documentation added (or pr:no public docs PR label added if not required)
• CHANGELOG.md updated (or pr:no changelog PR label added if not required)

[joeyorlando]

added indices to speed up querying these objects. These are the two filter patterns we use when querying these objects.

[joeyorlando]

the main issue here seemed to be Slack sending duplicate events to our API endpoint, shortly after one another, which led to this issue.

Example from logs (check trace IDs e3691dda80bd9e67476ceafb68c90a8f/2917201084877566781 and 978e7af66c11d0a680ce8175afdbda6f/15112916125666851927)

According to Django's docs, the solution to this is to use get_or_create:

Returns a tuple of (object, created), where object is the retrieved or created object and created is a boolean specifying whether a new object was created.

This is meant to prevent duplicate objects from being created when requests are made in parallel, and as a shortcut to boilerplatish code. For example:

try:
    obj = Person.objects.get(first_name="John", last_name="Lennon")
except Person.DoesNotExist:
    obj = Person(first_name="John", last_name="Lennon", birthday=date(1940, 10, 9))
    obj.save()

Here, with concurrent requests, multiple attempts to save a Person with the same parameters may be made. To avoid this race condition, the above example can be rewritten using get_or_create() like so:

[Ferril]

I think it's better to check len(text) before creating ResolutionNoteSlackMessage. Too long text may cause issues either with saving it to the db or displaying it in Slack 🤔

[joeyorlando]

👍

do you happen to know why there is this condition?:

if slack_thread_message.added_to_resolution_note:

if that can be removed, we can still use get_or_create

[joeyorlando]

alternative solution is to keep the separate get/create calls as it was, and add another try/except when creating, and catch any possible IntegrityErrors (but this seems a bit messier imo)

[Ferril]

ResolutionNoteSlackMessage is a message from alert group thread that potentially can be added to resolution notes.

It looks like we post warning message about too long text only either for messages that had already been added to resolution notes or for new messages in thread 🤔
If we post normal message and then edit it to make it long without adding to resolution notes, there won't be any warnings and the "Add Resolution notes" modal window in Slack will still have the old version of the message.
I think we can remove the check if slack_thread_message.added_to_resolution_note and post warning message in any case.

[Ferril]

I would change the message a bit. Something like "Unable to show the message in Resolution Notes..."