CSC/ECE 517 Spring 2022 - E2243. Refactor student teams functionality

This page contains information about Expertiza Issue E2243. Refactor student teams functionality which was a project in CSC517 Spring 2022.

Please see below for a description of the project.

Background

Users & Participants: Everyone who took the OODD class is a user in expertiza, and instructors can add users as participants in an assignment so that they can access it. Almost everything within Assignments is done by participants, not users. That is, everything except teams_users. In the documentation, it can be noted that the team_users table references users instead of participants. This anomaly causes problems with how student teams are rendered in the UI, and it doesn’t go well with the new functionality that were recently introduced.

teams_users should be changed to teams_participants. the team_id, user_id mapping in this table should be changed to team_id, participant_id. All the references of user_id should be updated to use participant_id.

Schema Changes

ER diagram for updated schema

Data Migration

Analysis

Participants contains user_id attribute which is a foreign key from users table. teams_users contains user_id which is also a foreign key from users table. Although the user_id field corresponds to same attribute, we cannot use this attribute alone to find the respective participant id because user_id is not a primary key in the participants table. i.e. same user_id can be associated with multiple participants. This is because in expertiza, all the users are stored in users table but, for each assignment, for each user, an entry is added in participants table. So, each user will have an entry in participants tables for all the assignments.

Assignment contains participants list (Assignment has_many Participant). Since a user can have only one entry in the participants table for each assignment, (assignment_id, user_id) pair will have only one participant id associated with it.

Finding Assignment ID By Team ID

teams_users table contains team_id, user_id and duty_id. Each team is associated with an assignment. parent_id attribute in the teams table corresponds to assignment id. So, team_id in the teams_users table can be used to get the Team object from which we can fetch the assignment ID (parent_id).

Code snippet to fetch assignment_id based on team_id assignment_id = Team.find(team_id).select(:parent_id)

Finding Participant ID By Assignment ID and User ID

Assignment object can be fetched using the assignment ID. Each assignment contains participants list. Participant object contains user_id attribute. Since, a user can have only one entry in participants table for an assignment, we can use user_id to find the user's participant_id from this list.

Code snippet to fetch participant_id based on assignment_id and user_id participant_id = Assignment.find(assignment_id).participants.find_by(:user_id user_id)

Brute Force Data Migration

The above mentioned code snippets can be used for each tuple in the teams_users table.

Brute Force Code Snippet TeamsUser.all.each do |teamsUser|

   assignment_id = Team.find(teamsUser.team_id).select(:parent_id)
   participant_id = Assignment.find(assignment_id).participants.find_by(:user_id teamsUser.user_id)
   teamsUser.update_attribute(:participant_id, participant_id)

end

Efficient Data Migration

In the brute force approach, db calls are made multiple times inside the loop. Moving the db calls out of the loop will give us a more efficient solution.

Steps:

1. Load all the TeamUser objects.
2. Load all the Team objects for all the team_ids in TeamUser object
3. Create a map with team_id as key and assignment_id as value. The resultant map usage: map[team_id] = assignment_id
4. Load all the Assignment objects for all the assignment_ids from the map in the previous step. Also eager fetch participants along with the assignments.
5. Create a nested map with assignment_id and user_id as key and participant_id as value. The resultant map usage: map[assignment_id][user_id] = participant_id
6. For all TeamUser objects, find the participant_id from the maps generated from the previous steps and update the participant_id attribute.

In this approach, we make a total of 3 db calls which is way better than the previous approach.