(Postgres) Rails with ulid primary keys

config application.rb

module SomeApp
  class Application < Rails::Application
    config.active_record.schema_format = :sql

    config.generators do |generator|
      generator.orm :active_record, primary_key_type: :ulid
    end
  end
end

db migrate 1_create_ulid_function.rb

class CreateUlidFunction < ActiveRecord::Migration[7.0]
  def change
    execute <<~SQL
      --
      -- SOURCE: https://github.com/geckoboard/pgulid
      --
      -- pgulid is based on OK Log's Go implementation of the ULID spec
      --
      -- https://github.com/oklog/ulid
      -- https://github.com/ulid/spec
      --
      -- Copyright 2016 The Oklog Authors
      -- Licensed under the Apache License, Version 2.0 (the "License");
      -- you may not use this file except in compliance with the License.
      -- You may obtain a copy of the License at
      --
      -- http://www.apache.org/licenses/LICENSE-2.0
      --
      -- Unless required by applicable law or agreed to in writing, software
      -- distributed under the License is distributed on an "AS IS" BASIS,
      -- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      -- See the License for the specific language governing permissions and
      -- limitations under the License.
      
      CREATE EXTENSION IF NOT EXISTS pgcrypto;
      CREATE FUNCTION generate_ulid()
          RETURNS TEXT
      AS $$
      DECLARE
      -- Crockford's Base32
      encoding   BYTEA = '0123456789ABCDEFGHJKMNPQRSTVWXYZ';
      timestamp  BYTEA = E'\\\\000\\\\000\\\\000\\\\000\\\\000\\\\000';
      output     TEXT = '';
      unix_time  BIGINT;
      ulid       BYTEA;
      BEGIN
        -- 6 timestamp bytes
        unix_time = (EXTRACT(EPOCH FROM NOW()) * 1000)::BIGINT;
      timestamp = SET_BYTE(timestamp, 0, (unix_time >> 40)::BIT(8)::INTEGER);
      timestamp = SET_BYTE(timestamp, 1, (unix_time >> 32)::BIT(8)::INTEGER);
      timestamp = SET_BYTE(timestamp, 2, (unix_time >> 24)::BIT(8)::INTEGER);
      timestamp = SET_BYTE(timestamp, 3, (unix_time >> 16)::BIT(8)::INTEGER);
      timestamp = SET_BYTE(timestamp, 4, (unix_time >> 8)::BIT(8)::INTEGER);
      timestamp = SET_BYTE(timestamp, 5, unix_time::BIT(8)::INTEGER);
      
        -- 10 entropy bytes
        ulid = timestamp || gen_random_bytes(10);
      
        -- Encode the timestamp
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 0) & 224) >> 5));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 0) & 31)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 1) & 248) >> 3));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 1) & 7) << 2) | ((GET_BYTE(ulid, 2) & 192) >> 6)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 2) & 62) >> 1));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 2) & 1) << 4) | ((GET_BYTE(ulid, 3) & 240) >> 4)));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 3) & 15) << 1) | ((GET_BYTE(ulid, 4) & 128) >> 7)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 4) & 124) >> 2));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 4) & 3) << 3) | ((GET_BYTE(ulid, 5) & 224) >> 5)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 5) & 31)));
      
        -- Encode the entropy
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 6) & 248) >> 3));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 6) & 7) << 2) | ((GET_BYTE(ulid, 7) & 192) >> 6)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 7) & 62) >> 1));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 7) & 1) << 4) | ((GET_BYTE(ulid, 8) & 240) >> 4)));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 8) & 15) << 1) | ((GET_BYTE(ulid, 9) & 128) >> 7)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 9) & 124) >> 2));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 9) & 3) << 3) | ((GET_BYTE(ulid, 10) & 224) >> 5)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 10) & 31)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 11) & 248) >> 3));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 11) & 7) << 2) | ((GET_BYTE(ulid, 12) & 192) >> 6)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 12) & 62) >> 1));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 12) & 1) << 4) | ((GET_BYTE(ulid, 13) & 240) >> 4)));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 13) & 15) << 1) | ((GET_BYTE(ulid, 14) & 128) >> 7)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 14) & 124) >> 2));
      output = output || CHR(GET_BYTE(encoding, ((GET_BYTE(ulid, 14) & 3) << 3) | ((GET_BYTE(ulid, 15) & 224) >> 5)));
      output = output || CHR(GET_BYTE(encoding, (GET_BYTE(ulid, 15) & 31)));
      
        RETURN output;
      END
      $$
      LANGUAGE plpgsql
      VOLATILE;
      
      --- https://github.com/geckoboard/pgulid/issues/4#issue-777696674
      create domain ulid as text
          default generate_ulid()
          not null
      constraint ulid_length_check check(char_length(value) = 26)
      constraint ulid_upper_bound check(value<='7ZZZZZZZZZZZZZZZZZZZZZZZZZ');
    SQL
  end
end