Rails migration adding PostgreSQL index for LIKE when the pattern is both left-anchored and right-anchored

postgresql_like_index.rb

# It supports queries like:
#   ModelName.where(ModelName.arel_table[:columnname].lower.matches 'searchterm')

class PostgresqlLikeIIndex < ActiveRecord::Migration
  def up
    enable_extension 'pg_trgm'
    execute <<~SQL
      CREATE INDEX index_tablename_on_columnname_lower
        ON tablename USING gin (lower(columnname) gin_trgm_ops)
    SQL
  end

  def down
    execute 'DROP INDEX index_tablename_on_columnname_lower'
    disable_extension 'pg_trgm'
  end
end

LIKE / ILIKE indexing: http://web.archive.org/web/20200723085756/https://www.cybertec-postgresql.com/en/postgresql-more-performance-for-like-and-ilike-statements/