PostgreSQL, register custom domains. Closes #14305.

This patch registers custom domains in our OID-type_map.
They will behave exactly as the type specified by `pg_type.typbasetype`.

/cc @matthewd

3 files changed, 68 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index 0235e652d3..1aeba4f856 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   The PostgreSQL adapter supports custom domains. Fixes #14305.
+
+    *Yves Senn*
+
 *   PostgreSQL `Column#type` is now determined through the corresponding OID.
     The column types stay the same except for enum columns. They no longer have
     `nil` as type but `enum`.
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index c31fe96842..e8719d5269 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -582,7 +582,7 @@ module ActiveRecord
         def initialize_type_map(type_map)
           if supports_ranges?
             result = execute(<<-SQL, 'SCHEMA')
-              SELECT t.oid, t.typname, t.typelem, t.typdelim, t.typinput, r.rngsubtype
+              SELECT t.oid, t.typname, t.typelem, t.typdelim, t.typinput, r.rngsubtype, t.typtype, t.typbasetype
               FROM pg_type as t
               LEFT JOIN pg_range as r ON oid = rngtypid
             SQL
@@ -593,6 +593,7 @@ module ActiveRecord
             SQL
           end
           ranges, nodes = result.partition { |row| row['typinput'] == 'range_in' }
+          domains, nodes = nodes.partition { |row| row['typtype'] == 'd' }
           leaves, nodes = nodes.partition { |row| row['typelem'] == '0' }
           arrays, nodes = nodes.partition { |row| row['typinput'] == 'array_in' }
 
@@ -626,6 +627,15 @@ module ActiveRecord
             range = OID::Range.new subtype
             type_map[row['oid'].to_i] = range
           end
+
+          # populate domain types
+          domains.each do |row|
+            if base_type = type_map[row["typbasetype"].to_i]
+              type_map[row['oid'].to_i] = base_type
+            else
+              warn "unknown base type (OID: #{row["typbasetype"].to_i}) for domain #{row["typname"]}."
+            end
+          end
         end
 
         FEATURE_NOT_SUPPORTED = "0A000" #:nodoc:
diff --git a/activerecord/test/cases/adapters/postgresql/domain_test.rb b/activerecord/test/cases/adapters/postgresql/domain_test.rb
new file mode 100644
index 0000000000..fdf5ce974d
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/domain_test.rb
@@ -0,0 +1,53 @@
+# -*- coding: utf-8 -*-
+require "cases/helper"
+require 'active_record/base'
+require 'active_record/connection_adapters/postgresql_adapter'
+
+class PostgresqlDomainTest < ActiveRecord::TestCase
+  class PostgresqlDomain < ActiveRecord::Base
+    self.table_name = "postgresql_domains"
+  end
+
+  def setup
+    # reset connection to bust all cached statement plans
+    connection_spec = ActiveRecord::Base.remove_connection
+    ActiveRecord::Base.establish_connection(connection_spec)
+
+    @connection = ActiveRecord::Base.connection
+    @connection.transaction do
+      @connection.execute "CREATE DOMAIN custom_money as numeric(8,2)"
+      @connection.create_table('postgresql_domains') do |t|
+        t.column :price, :custom_money
+      end
+    end
+
+    # reload type map after creating the enum type
+    @connection.send(:reload_type_map)
+  end
+
+  teardown do
+    @connection.execute 'DROP TABLE IF EXISTS postgresql_domains'
+    @connection.execute 'DROP DOMAIN IF EXISTS custom_money'
+  end
+
+  def test_column
+    column = PostgresqlDomain.columns_hash["price"]
+    assert_equal :decimal, column.type
+    assert_equal "custom_money", column.sql_type
+    assert column.number?
+    assert_not column.text?
+    assert_not column.binary?
+    assert_not column.array
+  end
+
+  def test_domain_acts_like_basetype
+    PostgresqlDomain.create price: ""
+    record = PostgresqlDomain.first
+    assert_nil record.price
+
+    record.price = "34.15"
+    record.save!
+
+    assert_equal BigDecimal.new("34.15"), record.reload.price
+  end
+end