JRuby: How to use the ActiveRecord postgresql adapter without `pg`, which is written in C?

Question

Trying to use ActiveRecord with Postgres on JRuby 9.3.3.0 on Mac Catalina 10.15.7, with the Postgres server running. Followed the instructions at github.com/jruby/activerecord-jdbc-adapter per @hmdne advice. I see the error:

NameError: uninitialized constant ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::PG

This is my code:

require 'active_record'
require 'activerecord-jdbc-adapter' if defined? JRUBY_VERSION

ActiveRecord::Base.establish_connection(
  adapter: "postgresql",
  host: "localhost",
  database: "test",
  username: "postgres",
  password: "password")

The stack trace contains the entry

/Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/postgresql_adapter.rb:937

Line 937 is

class MoneyDecoder < PG::SimpleDecoder # :nodoc:

So ActiveRecord is subclassing a class in PG, but PG won't build on JRuby. Tried doing 'gem install activerecord-postgresql-adapter' but the install fails because that gem also depends on the 'pg' gem.

Tried the line "require 'activerecord-jdbcpostgresql-adapter' if defined? JRUBY_VERSION" either instead of or in addition to the require 'activerecord-jdbc-adapter' but I still get the same 'uninitialized constant ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::PG', and essentially the same stack trace.

I'm using the latest versions of all the gems. Thanks!!!

/bin/zsh -c "bash -c '/Users/test/.rvm/bin/rvm jruby-9.3.3.0 do /Users/test/.rvm/rubies/jruby-9.3.3.0/bin/jruby /Users/test/RubymineProjects/glimmer/TaskTimer2/lib/testSO.rb'"
NameError: uninitialized constant ActiveRecord::ConnectionAdapters::PostgreSQLAdapter::PG
        load_missing_constant at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activesupport-6.1.4.6/lib/active_support/dependencies.rb:603
                const_missing at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activesupport-6.1.4.6/lib/active_support/dependencies.rb:213
    <class:PostgreSQLAdapter> at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/postgresql_adapter.rb:937
  <module:ConnectionAdapters> at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/postgresql_adapter.rb:73
        <module:ActiveRecord> at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/postgresql_adapter.rb:45
                       <main> at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/postgresql_adapter.rb:22
                      require at org/jruby/RubyKernel.java:1017
                      require at /Users/test/.rvm/rubies/jruby-9.3.3.0/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:85
                      require at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activesupport-6.1.4.6/lib/active_support/dependencies.rb:332
              load_dependency at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activesupport-6.1.4.6/lib/active_support/dependencies.rb:299
                      require at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activesupport-6.1.4.6/lib/active_support/dependencies.rb:332
          resolve_pool_config at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:1205
         establish_connection at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_adapters/abstract/connection_pool.rb:1046
         establish_connection at /Users/test/.rvm/gems/jruby-9.3.3.0/gems/activerecord-6.1.4.6/lib/active_record/connection_handling.rb:52
                       <main> at /Users/test/RubymineProjects/glimmer/TaskTimer2/lib/testSO.rb:4

Process finished with exit code 1