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https://github.com/sir-ragna/flaskvotes
Very simple voting example
https://github.com/sir-ragna/flaskvotes
Last synced: 8 days ago
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Very simple voting example
- Host: GitHub
- URL: https://github.com/sir-ragna/flaskvotes
- Owner: sir-ragna
- Created: 2020-12-19T23:37:27.000Z (about 4 years ago)
- Default Branch: main
- Last Pushed: 2020-12-20T11:44:52.000Z (about 4 years ago)
- Last Synced: 2024-11-14T01:31:38.657Z (2 months ago)
- Language: Python
- Size: 10.7 KB
- Stars: 1
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: readme.md
Awesome Lists containing this project
README
# Tracking votes on content
Trying to track the number on votes on the content can be tricky.
Here is a naive way to track votes and a proposed solution.
|post_id|post_content|score|
|:------|:-----------|----:|
|1 |'hello' |3 |
When a user votes we increment or decrement the score counter based upon
our user either upvoting(+1) or downvoting(-1).
Imagine our user _Steve_ wants to cast a vote, how are we going to verify
that _Steve_ hasn't already voted? The solution to this is to track for
which posts _Steve_ already has voted.
Ideally however we do not separately track all the votes and the scores
we are simply able to calculate the score by summing all the votes.
|post_id|post_content|
|:------|:-----------|
|1 |hello |
|2 |Goodbye |
Our voting table.
|post_id|username|rating|
|:------|:-------|-----:|
|1 |Steve | 1|
|1 |Bert | -1|
|1 |Rob | 1|
|1 |Olaf | 1|
Then when we need to retrieve the score we SUM the rating to get our
total score.
```sql
SELECT post_id, SUM(rating) as 'score'
FROM votes
GROUP BY post_id
```
## Retrieving the top 5 posts
Imagine we want to retrieve the top 5 posts. A naive way of doing this
might be to write the following query.
```sql
SELECT posts.post_id, SUM(votes.rating) as 'score'
FROM posts
JOIN votes on posts.post_id = votes.post_id
GROUP BY posts.post_id
ORDER BY score DESC
LIMIT 5
```
This however will not include posts that have not received any votes yet.
|post_id|score|
|:------|----:|
|1 | 2|
A `JOIN` is an `INNER JOIN` by default, this means you'll only get
entries when something is found both in the `votes` table and in the
`posts` table. Here the fix is to create a `LEFT JOIN`.
This will also return the posts that did not receive any rating.
|post_id|score|
|:------|----:|
|1 | 2|
|2 | NULL|
This is already workable. Yet I prefer not having to deal with the
_NULL_ values in my Python code, hence I will ask to return 0 whenever
_NULL_ manifests. This can be achieved with the following code.
```sql
CASE WHEN votes.rating IS NULL THEN 0 ELSE votes.rating
```
This is the equivalent of an `if` statement.
Our full query as found in the `get_top_posts`-function.
```sql
SELECT posts.post_id, SUM(
CASE WHEN votes.rating IS NULL
THEN 0
ELSE votes.rating
END) as 'score'
FROM posts
LEFT JOIN votes on posts.post_id = votes.post_id
GROUP BY posts.post_id
ORDER BY score DESC
LIMIT 5
```