Proposed Changes

(Describe your changes here. Also describe the motivation for your changes: what problem do they solve, or how do they improve the application or codebase? If this pull request fixes an open issue, use a keyword to link this pull request to the issue.)

This improves the efficiency of the Assignment#summary_json method, which is used in the AssignementsController#summary route (json format). Notable changes are:

• Fixed an N+1 query for loading result marks
• Avoid allocations of model objects (e.g., Result, Grouping), instead preferring Ruby arrays/hashes
• Prefer using pluck to pluck_to_hash
• Leverage more postgres aggregation functions to group data, rather than Ruby's Enumerable#group_by method
• Eliminate redundant queries for total mark calculations and number assigned/marked (for instructors only)

On my development environment with ~1200 students and groups, these changes reduced the number of queries from 1248 to 27 and response time from ~5000ms to ~400ms when this summary is invoked by an instructor.

Type of Change

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Checklist

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