Fix reverse dependencies by using distinct

[federicoaldunate]

Fix reverse dependencies bug

Another example: https://rubygems.org/gems/rspec/reverse_dependencies

Description

Reverse dependencies are being repeated.
Linked issue: #5199

Tried to solve this at least in the user facing controller side of things.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.35%. Comparing base (b827011) to head (a1c473f).
Report is 12 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #5566       +/-   ##
===========================================
+ Coverage   71.71%   94.35%   +22.63%     
===========================================
  Files         453      453               
  Lines        9609     9470      -139     
===========================================
+ Hits         6891     8935     +2044     
+ Misses       2718      535     -2183     

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[segiddins]

I'm a bit concerned if this will have a performance impact, can you share the generated queries and I can explain analyze them?

[simi]

I'm a bit concerned if this will have a performance impact, can you share the generated queries and I can explain analyze them?

I'll check.

[federicoaldunate]

I'm a bit concerned if this will have a performance impact, can you share the generated queries and I can explain analyze them?
I don't think it will have a big impact, this is the difference between the queries generated:
Before

SELECT rubygems.*
FROM rubygems
JOIN versions
  ON rubygems.id = versions.rubygem_id
JOIN dependencies
  ON versions.id = dependencies.version_id
JOIN gem_downloads
  ON gem_downloads.version_id = 0
 AND gem_downloads.rubygem_id = rubygems.id
WHERE dependencies.rubygem_id = {the_ruby_gem_id}
  AND versions.indexed = TRUE
  AND versions.position = 0
ORDER BY gem_downloads.count DESC;

After

SELECT DISTINCT rubygems.*, gem_downloads.count
FROM rubygems
JOIN versions
  ON rubygems.id = versions.rubygem_id
JOIN dependencies
  ON versions.id = dependencies.version_id
JOIN gem_downloads
  ON gem_downloads.version_id = 0
 AND gem_downloads.rubygem_id = rubygems.id
WHERE dependencies.rubygem_id = {the_ruby_gem_id}
  AND versions.indexed = TRUE
  AND versions.position = 0
ORDER BY gem_downloads.count DESC;

[federicoaldunate]

@simi @segiddins, let me know what you think.