Rails-UniqBeforePluck.md

Pattern: Use of pluck before uniq/distinct

Issue: -

Description

Prefer the use of uniq (or distinct) before pluck instead of after.

The use of uniq before pluck is preferred because it executes within the database.

This rule has two different enforcement modes. When the EnforcedStyle is conservative (the default) then only calls to pluck on a constant (i.e. a model class) before uniq are added as offenses.

When the EnforcedStyle is aggressive then all calls to pluck before uniq are added as offenses. This may lead to false positives as the rule cannot distinguish between calls to pluck on an ActiveRecord::Relation vs a call to pluck on an ActiveRecord::Associations::CollectionProxy.

Examples

# bad
Model.pluck(:id).uniq

# good
Model.uniq.pluck(:id)

# this will return a Relation that pluck is called on
Model.where(...).pluck(:id).uniq

# an association on an instance will return a CollectionProxy
instance.assoc.pluck(:id).uniq

Default configuration

Attribute	Value
EnforcedStyle	conservative
SupportedStyles	conservative, aggressive

Further Reading

• RuboCop - Rails/UniqBeforePluck