During the process of generatinng report for problem responses,
there are two places where N + 1 query problem exist. In both
cases, `StudentModule` objects are fetched and looped over where
`student.username` field for each object is accessed. This result
in a seperate database call to get the username for each student
response.
This problem is fixed by creating a join to fetch the related
table in the original query using `select_related`. In a test
conducted on report having 5000 `StudentModule` objects, the
number of queries for the request reduced from 8363 to 29. The
total time taken for the task reduced from 23764 ms to 7394 ms.
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