New LearningResourcePrice model

[mbertrand]

What are the relevant tickets?

PR 1 of 5 to address https://github.com/mitodl/hq/issues/5134 and https://github.com/mitodl/hq/issues/4685

Description (What does it do?)

• Adds a LearningResourcePrice model with two fields (amount, currency)
• Adds a many-to-many relation between LearningResource and LearningResourcePrice, also between LearningResourceRun and LearningResourcePrice (named resource_prices)
• Updates QuerySet classes to avoid n+1 queries
• Updates the search index schema with addition of the new resource_prices field
• Adds a new python package pycountry to validate currency codes during ETL pipeline runs

How can this be tested?

• If you don't already have some courses with prices, run these commands on the main branch:

  ./manage.py backpopulate_mitxonline_data
  ./manage.py backpopulate_xpro_data
  

• Log in as an admin user to avoid caching and go to http://open.odl.local:8062/search?platform=mitxonline&platform=xpro, you will see a mix of courses that should all either be paid with certificate (xpro) or free with a paid certificate option (mitxonline). If you click on a course card you will see the same price in the drawer.
• Switch to this branch, run docker compose build web celery (new python package) and restart containers. Make sure the new migrations complete successfully.
• Go to http://open.odl.local:8062/search?platform=mitxonline&platform=xpro again. Everything should still look the same.
• Click on a result and check the API response for that resource. There should be a resource_prices attribute for the resource and each of it's runs, with amount and currency attributes.
• Run ./manage.py update_index --courses --programs, then wait a minute or 2.
• Go to http://open.odl.local:8062/search?platform=mitxonline&platform=xpro again. It should still look the same, and if you inspect search API results, the resource_prices field should be there too.
• Run ./manage.py recreate_index --all, it should complete without errors.
• Check and uncheck the "Free" checkbox on the search page. The results should change as expected.
• Running the following pipelines should still complete successfully (you'll need the appropriate env values from RC for SEE_* and EDX_API_*):

  ./manage.py backpopulate_sloan_data
  ./manage.py backpopulate_mit_edx_data [--api_course_file=edx.json --api_program_datafile=edx_programs.json]
  

• Use the django debug toolbar to measure the # and speed of SQL queries for the URL http://api.open.odl.local:8063/api/v1/learning_resources/?platform=mitxonline. It should not be significantly slower than the same url on the main branch, but there will be 2 additional queries.

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• Finally if you want to revert your price data before you go back to the main branch, run this and the prices field should be restored with values:

  ./manage.py migrate learning_resources 0070_learningresource_location
  

Additional Context

• Most data sources always have prices in USD. Exceptions are Sloan and MIT edX, so their ETL pipelines have been adjusted to extract the currency from their API's.
• There will be 4 subsequent PR's before https://github.com/mitodl/hq/issues/5134 is closed:
  • 2: Change frontend to use the resource_prices field instead of prices
  • 3: Modify the LearningResource.prices and LearningResourceRun.prices fields to be the same as resource_prices, and update schema. (Note: this will cause index updates to fail until a reindex completes)
  • 4: Change frontend to use prices field again
  • 5: Remove resource_prices from models and schemas.

[ChristopherChudzicki]

This looks good 👍

On thing I noticed is that when I ran the indexing commands, Django told me:

WARNINGS:
learning_resources.LearningResource.resource_prices: (fields.W340) null has no effect on ManyToManyField.
learning_resources.LearningResourceRun.resource_prices: (fields.W340) null has no effect on ManyToManyField.
Operations to perform

[mbertrand]

@ChristopherChudzicki Good catch, I just updated the model definition/migration for those fields