Fix sensei email generating multiple queries on page load

[Imran92]

Resolves #6815

Proposed Changes

• Updated the check before initializing the email so that instead of generating multiple queries before enabling emails, we can do only one which improves the performance. It triggers meta cache queries, but they are very small and fast, unlike the join queries.

Testing Instructions

1. You should have a way to monitor the queries (Can use the Query Monitor plugin)
2. Check the generated queries when you reload a page
3. You should see only one sensei_email query logged there

###Before

Screen.Recording.2023-04-18.at.2.59.54.PM.mov

###After

Pre-Merge Checklist

• PR title and description contain sufficient detail and accurately describe the changes
• Acceptance criteria is met
• Decisions are publicly documented
• Adheres to coding standards (PHP, JavaScript, CSS, HTML)
• All strings are translatable (without concatenation, handles plurals)
• Follows our naming conventions (P6rkRX-4oA-p2)
• Hooks (p6rkRX-1uS-p2) and functions are documented
• New UIs are responsive and use a mobile-first approach
• New UIs match the designs
• Different user privileges (admin, teacher, subscriber) are tested as appropriate
• Code is tested on the minimum supported PHP and WordPress versions
• User interface changes have been tested on the latest versions of Chrome, Firefox and Safari
• "Needs Documentation" label is added if this change requires updates to documentation
• Known issues are created as new GitHub issues

[codecov]

Codecov Report

Merging #6819 (f82de23) into trunk (ef6cee6) will decrease coverage by 0.04%.
Report is 10 commits behind head on trunk.
The diff coverage is 59.25%.

@@             Coverage Diff              @@
##              trunk    #6819      +/-   ##
============================================
- Coverage     49.80%   49.76%   -0.04%     
- Complexity    10650    10653       +3     
============================================
  Files           586      586              
  Lines         45047    45055       +8     
  Branches        402      402              
============================================
- Hits          22434    22420      -14     
- Misses        22286    22308      +22     
  Partials        327      327              

Files Changed	Coverage Δ
includes/admin/class-sensei-learners-main.php	5.30% <0.00%> (ø)
includes/internal/emails/class-email-generator.php	82.60% <0.00%> (-17.40%)	⬇️
...ils/generators/class-email-generators-abstract.php	41.66% <33.33%> (+41.66%)	⬆️
includes/internal/emails/class-email-sender.php	99.02% <100.00%> (ø)
...ernal/emails/generators/class-course-completed.php	100.00% <100.00%> (ø)
...nternal/emails/generators/class-course-created.php	100.00% <100.00%> (+6.06%)	⬆️
...nternal/emails/generators/class-course-welcome.php	100.00% <100.00%> (+4.16%)	⬆️
...al/emails/generators/class-new-course-assigned.php	96.29% <100.00%> (ø)
...s/internal/emails/generators/class-quiz-graded.php	90.62% <100.00%> (ø)
...ails/generators/class-student-completes-course.php	97.05% <100.00%> (ø)
... and 6 more

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[jom]

Hi @Imran92! Thanks for picking up this issue. This is an improvement, but I wonder if there is a way to still limit the meta queries... I'm still seeing ~38 related to this (without object caching). One way might be caching this, but then you'd need to handle invalidation. Did y'all consider delaying the check if an email was active until later on? One possibility would be a proxy callback in the hooks in the email generators' init methods that could check, or even just a check in the Email_Generators_Abstract::send_email_action method.

[Imran92]

Thanks a lot for the review @jom! I've updated the PR to use a intermediate callback in the middle. Checking at the time of send_email_action would be simpler, but in that case, all the processing to prepare the email data would still be done even if the email was disabled. There are some changes in pro related to this. Please take a look again when possible.
Thanks!

[donnapep]

Seems to work! 👍🏻

[donnapep]

This one is pending a fix. @Imran92 would you mind describing what's left to do for this one so that it's not lost? Thx!

[Imran92]

Suppose someone has both sensei and sensei-pro and updates only sensei but not sensei pro or delays updating, as the check for being active has been moved from core to individual email generator. In that case, their pro emails will still be active even when deactivated during that time frame. We need to put a check in place to prevent that from happening.

[Imran92]

Both of the issues mentioned #6819 (comment) and #6819 (comment) are taken care of in d9722c2 and 083af2d :)

[donnapep]

Emails are still working, and I no longer see 1 query per email. 🎉 The 1 query I do see on the emails page isn't the same as the screenshot in the PR description though:

[Imran92]

The 1 query I do see on the emails page isn't the same as the screenshot in the PR description though:

Yeah, I believe it's the one that fetches the emails to populate the list we see when we're on Sensei LMS -> Settings -> Emails -> Student Emails. When we're on any other page, it shouldn't generate any query ☺️