Buckets

One more feature for the reports bucket

This feature uses the width_bucket() function to return results or produce calculations in which the results fall into the configured buckets. PostgreSQL Docs

You can disable this feature using config.buckets.

How to

There are two main ways of using the .buckets function. Providing a Range or an Array. Both ways work accordingly: Simply querying the records and getting a map/Hash where the key is the proper bucket (not the bucket number), and the value is the array of records; or using calculations like .count.

# Range
User.buckets(:age, 0..100, count: 5)             # Expect { (0...20) => [...], (20...40) => [...], ... }
User.buckets(:age, 0..100, count: 10).count      # Expect { (0...10) => N, (10...20) => N, ... }

# Array
User.buckets(:role, %w[visitor manager admin])   # Expect { nil => [...], 'visitor' => [...], ... }
                                                 # nil represents values that did not fall on any bucket

Here is a list of all options that can be used to configure this operation:

• count: When using a numeric range, this represents the number of buckets to divide the results (it DOES NOT work as .step);
• cast: A shorthand for casting the values of the given Array;
• as: The name of the attribute added to the query and subsequent operations. Default bucket.

Here is a full example that will count the number of users created each year from 2010 until 2025.

keys = 16.times.map { |add| Date.new(2010 + add) }
User.buckets(:created_at, keys, cast: :date).count
# Expect { Date.new(2010) => N, Date.new(2011) => N, ... }

SELECT COUNT(*) AS "count_all", WIDTH_BUCKET("users"."created_at", ARRAY[...]::date[]) AS "bucket"
FROM "users"
GROUP BY "bucket";

Since the resulting bucket attribute is added to the resulting query, you can access the raw value from each record:

keys = 16.times.map { |add| Date.new(2010 + add) }
records = User.buckets(:created_at, keys, cast: :date).load

records.values.first.bucket       # Will return the numeric value of the bucket