fix(medusa): discounts service create validates against at-least 1 region

[riqwan]

What:

• introduces regions validation on creating a discount
  • you can only create a discount with at-least 1 valid region ID

Why:

A discount is validated against a region while being added to a cart. Any discount that is applied therefore needs to be associated with a valid region.

How:

As a first step, we introduce a validation into the discount create service. With this PR, discounts will always be associated with a region on creation of a discount.

There are some cases we need to handle:

• When a region is deleted, what happens to the discount?
• When a discount is updated with an empty regions array, the discount ends up in a state with no regions.
• What do we do about existing discounts that have no region?

Testing:

Unit tests:

• Add valid regions to all existing unit tests
• Unsuccessful creation with invalid regions

Integration tests:

• Add valid regions to all existing integration tests
• Fails to create a discount if the regions contains an invalid regionId
• Fails to create a discount if regions are not present

FIXES CORE-873

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🦋 Changeset detected

Latest commit: dbe2524

The changes in this PR will be included in the next version bump.

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@medusajs/medusa	Patch

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[adrien2p]

Very good, only minor comments 🚀

[adrien2p]

@riqwan can I get you to add a description on the PR and link the linear issue the way I sent you :)

[adrien2p]

One last comment and one thing to look at. We should probably update the service method that creates the discounts to enforce at least one. At the moment it accepts optional regions properties but it might be wrong too. Could you check please?

[adrien2p]

LGTM, few minor comments left and I think we are good to go ahah @olivermrbl do you want to run a review?

[adrien2p]

LGTM 🎉 one last comment ahah

[adrien2p]

LGTM 🎉 very nice boy scoot session included 💪

[adrien2p]

@riqwan I suggest to also wait the approval from @olivermrbl to have a second pair of eyes

[olivermrbl]

Really solid work @riqwan! Don't have anything to add 🥳

When a discount is updated with an empty regions array, the discount ends up in a state with no regions.

Ideally, we would add a check similar to this PR. Not super urgent, but feel free to create a Linear issue and tackle that too 💪

What do we do about existing discounts that have no region?

I don't think we have to do anything. Worst case, the invalid discounts throw a 400 + sends an appropriate error message when applied to carts.