Ensure tags are unique within an assignment

[donny-wong]

Proposed Changes

We want to make tags unique within an assignment. A validation rule was added to the Tag model to ensure the name was unique to an assignment.

...

Screenshots of your changes (if applicable)

e.g:
When I tried to create another tag that already exist ("tag_1") in the same assignment, it would not permit me:

With another assignment for the same course, I was able to when this name was already used from the above assignment:

Associated documentation repository pull request (if applicable)

Type of Change

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Type	Applies?
🚨 Breaking change (fix or feature that would cause existing functionality to change)
✨ New feature (non-breaking change that adds functionality)
🐛 Bug fix (non-breaking change that fixes an issue)	x
🎨 User interface change (change to user interface; provide screenshots)
♻️ Refactoring (internal change to codebase, without changing functionality)
🚦 Test update (change that only adds or modifies tests)
📦 Dependency update (change that updates a dependency)
🔧 Internal (change that only affects developers or continuous integration)

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Questions and Comments

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[coveralls]

Pull Request Test Coverage Report for Build 13457613824

Details

• 4 of 4 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 91.863%

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Totals
Change from base Build 13436830841:	0.0%
Covered Lines:	41403
Relevant Lines:	44388

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💛 - Coveralls

[david-yz-liu]

@donny-wong good work, and good screenshots. In addition to the comment I left, you should use GitHub PR linking keywords to link this to the issue you created. See https://docs.github.com/en/issues/tracking-your-work-with-issues/using-issues/linking-a-pull-request-to-an-issue

[david-yz-liu]

Say tag names here, not just "tags"

[donny-wong]

Thank you @david-yz-liu for these helpful comments.