Support for PostgreSQL foreign tables

4 files changed, 128 insertions, 1 deletions

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index efe555374a..e2dc8045e2 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   Support for PostgreSQL foreign tables.
+
+    *fatkodima*
+
 *   Fix relation merger issue with `left_outer_joins`.
 
     *Mehmet Emin İNAÇ*
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
index c6e5122daf..b9d2f4da39 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql/schema_statements.rb
@@ -527,6 +527,14 @@ module ActiveRecord
           end
         end
 
+        def foreign_tables
+          query_values(data_source_sql(type: "FOREIGN TABLE"), "SCHEMA")
+        end
+
+        def foreign_table_exists?(table_name)
+          query_values(data_source_sql(table_name, type: "FOREIGN TABLE"), "SCHEMA").any? if table_name.present?
+        end
+
         # Maps logical Rails types to PostgreSQL-specific data types.
         def type_to_sql(type, limit: nil, precision: nil, scale: nil, array: nil, **) # :nodoc:
           sql = \
@@ -739,7 +747,7 @@ module ActiveRecord
 
           def data_source_sql(name = nil, type: nil)
             scope = quoted_scope(name, type: type)
-            scope[:type] ||= "'r','v','m'" # (r)elation/table, (v)iew, (m)aterialized view
+            scope[:type] ||= "'r','v','m','f'" # (r)elation/table, (v)iew, (m)aterialized view, (f)oreign table
 
             sql = "SELECT c.relname FROM pg_class c LEFT JOIN pg_namespace n ON n.oid = c.relnamespace".dup
             sql << " WHERE n.nspname = #{scope[:schema]}"
@@ -756,6 +764,8 @@ module ActiveRecord
                 "'r'"
               when "VIEW"
                 "'v','m'"
+              when "FOREIGN TABLE"
+                "'f'"
               end
             scope = {}
             scope[:schema] = schema ? quote(schema) : "ANY (current_schemas(false))"
diff --git a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
index 9ac5a8760e..ddc5a91286 100644
--- a/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb
@@ -318,6 +318,10 @@ module ActiveRecord
         postgresql_version >= 90300
       end
 
+      def supports_foreign_tables?
+        postgresql_version >= 90300
+      end
+
       def supports_pgcrypto_uuid?
         postgresql_version >= 90400
       end
diff --git a/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb b/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb
new file mode 100644
index 0000000000..4fa315ad23
--- /dev/null
+++ b/activerecord/test/cases/adapters/postgresql/foreign_table_test.rb
@@ -0,0 +1,109 @@
+# frozen_string_literal: true
+
+require "cases/helper"
+require "models/professor"
+
+if ActiveRecord::Base.connection.supports_foreign_tables?
+  class ForeignTableTest < ActiveRecord::TestCase
+    self.use_transactional_tests = false
+
+    class ForeignProfessor < ActiveRecord::Base
+      self.table_name = "foreign_professors"
+    end
+
+    class ForeignProfessorWithPk < ForeignProfessor
+      self.primary_key = "id"
+    end
+
+    def setup
+      @professor = Professor.create(name: "Nicola")
+
+      @connection = ActiveRecord::Base.connection
+      enable_extension!("postgres_fdw", @connection)
+
+      foreign_db_config = ARTest.connection_config["arunit2"]
+      @connection.execute <<-SQL
+        CREATE SERVER foreign_server
+          FOREIGN DATA WRAPPER postgres_fdw
+          OPTIONS (dbname '#{foreign_db_config["database"]}')
+      SQL
+
+      @connection.execute <<-SQL
+        CREATE USER MAPPING FOR CURRENT_USER
+          SERVER foreign_server
+      SQL
+
+      @connection.execute <<-SQL
+        CREATE FOREIGN TABLE foreign_professors (
+          id    int,
+          name  character varying NOT NULL
+        ) SERVER foreign_server OPTIONS (
+          table_name 'professors'
+        )
+      SQL
+    end
+
+    def teardown
+      disable_extension!("postgres_fdw", @connection)
+      @connection.execute <<-SQL
+        DROP SERVER IF EXISTS foreign_server CASCADE
+      SQL
+    end
+
+    def test_table_exists
+      table_name = ForeignProfessor.table_name
+      assert_not ActiveRecord::Base.connection.table_exists?(table_name)
+    end
+
+    def test_foreign_tables_are_valid_data_sources
+      table_name = ForeignProfessor.table_name
+      assert @connection.data_source_exists?(table_name), "'#{table_name}' should be a data source"
+    end
+
+    def test_foreign_tables
+      assert_equal ["foreign_professors"], @connection.foreign_tables
+    end
+
+    def test_foreign_table_exists
+      assert @connection.foreign_table_exists?("foreign_professors")
+      assert @connection.foreign_table_exists?(:foreign_professors)
+      assert_not @connection.foreign_table_exists?("nonexistingtable")
+      assert_not @connection.foreign_table_exists?("'")
+      assert_not @connection.foreign_table_exists?(nil)
+    end
+
+    def test_attribute_names
+      assert_equal ["id", "name"], ForeignProfessor.attribute_names
+    end
+
+    def test_attributes
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      assert_equal @professor.attributes, professor.attributes
+    end
+
+    def test_does_not_have_a_primary_key
+      assert_nil ForeignProfessor.primary_key
+    end
+
+    def test_insert_record
+      # Explicit `id` here to avoid complex configurations to implicitly work with remote table
+      ForeignProfessorWithPk.create!(id: 100, name: "Leonardo")
+
+      professor = ForeignProfessorWithPk.last
+      assert_equal "Leonardo", professor.name
+    end
+
+    def test_update_record
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      professor.name = "Albert"
+      professor.save!
+      professor.reload
+      assert_equal "Albert", professor.name
+    end
+
+    def test_delete_record
+      professor = ForeignProfessorWithPk.find(@professor.id)
+      assert_difference("ForeignProfessor.count", -1) { professor.destroy }
+    end
+  end
+end