Skip schema dumper when extension is not available

bin/console

@@ -9,7 +9,9 @@ def uri_from_test
   ENV['PG_URI_TEST']
 end
 
-ActiveRecord::Base.establish_connection(ARGV[0] || uri_from_test)
+uri = ARGV[0] || uri_from_test
+ActiveRecord::Base.establish_connection(uri)
+Timescaledb.establish_connection(uri)
 
 Timescaledb::Hypertable.find_each do |hypertable|
   class_name = hypertable.hypertable_name.singularize.camelize

lib/timescaledb.rb

@@ -17,11 +17,20 @@
 require_relative 'timescaledb/stats'
 require_relative 'timescaledb/stats_report'
 require_relative 'timescaledb/migration_helpers'
+require_relative 'timescaledb/extension'
 require_relative 'timescaledb/version'
 
 module Timescaledb
   module_function
 
+  def connection
+    Connection.instance
+  end
+
+  def extension
+    Extension
+  end
+
   def chunks
     Chunk.all
   end

lib/timescaledb/connection.rb

@@ -1,6 +1,11 @@
 require 'singleton'
 
 module Timescaledb
+  # Minimal connection setup for Timescaledb directly with the PG.
+  # The concept is use a singleton component that can query
+  # independently of the ActiveRecord::Base connections.
+  # This is useful for the extension and hypertable metadata.
+  # It can also #use_connection from active record if needed.
   class Connection
     include Singleton
 
@@ -34,10 +39,16 @@ def connected?
       [email protected]?
     end
 
+    # Override the connection with a raw PG connection.
+    # @param [PG::Connection] connection The raw PG connection.
+    def use_connection connection
+      @connection = connection
+    end
+
     private
 
     def connection
       @connection ||= PG.connect(@config)
     end
   end
-end
+end

lib/timescaledb/connection_handling.rb

@@ -1,16 +1,21 @@
 module Timescaledb
   class ConnectionNotEstablishedError < StandardError; end
 
-  # @param [String] config The postgres connection string.
+  module_function
+
+  # @param [String] config with the postgres connection string.
   def establish_connection(config)
     Connection.instance.config = config
   end
-  module_function :establish_connection
+
+  # @param [PG::Connection] to use it directly from a raw connection
+  def use_connection conn
+    Connection.instance.use_connection conn
+  end
 
   def connection
     raise ConnectionNotEstablishedError.new unless Connection.instance.connected?
 
     Connection.instance
   end
-  module_function :connection
-end
+end

lib/timescaledb/extension.rb

@@ -0,0 +1,23 @@
+module Timescaledb
+
+  # Provides metadata around the extension in the database
+  module Extension
+    module_function
+    # @return String version of the timescaledb extension
+    def version
+      @version ||= Timescaledb.connection.query_first(<<~SQL)&.version
+        SELECT extversion as version
+        FROM pg_extension
+        WHERE extname = 'timescaledb'
+      SQL
+    end
+
+    def installed?
+      version.present?
+    end
+
+    def update!
+      Timescaledb.connection.execute('ALTER EXTENSION timescaledb UPDATE')
+    end
+  end
+end

lib/timescaledb/schema_dumper.rb

@@ -7,14 +7,29 @@ module Timescaledb
   # * retention policies
   # * continuous aggregates
   # * compression settings
+  # It also ignores Timescale related schemas when dumping the schema.
+  # It also ignores dumping options as extension is not installed or no hypertables are available.
   module SchemaDumper
     def tables(stream)
       super # This will call #table for each table in the database
-      return unless Timescaledb::Hypertable.table_exists?
 
-      timescale_hypertables(stream)
-      timescale_retention_policies(stream)
-      timescale_continuous_aggregates(stream) # Define these before any Scenic views that might use them
+      if exports_timescaledb_metadata?
+        timescale_hypertables(stream)
+        timescale_retention_policies(stream)
+        timescale_continuous_aggregates(stream) # Define these before any Scenic views that might use them
+      end
+    end
+
+    # Ignore dumps in case DB is not eligible for TimescaleDB metadata.
+    # @return [Boolean] true if the extension is installed and hypertables are available, otherwise false.
+    private def exports_timescaledb_metadata?
+      # Note it's safe to use the raw connection here because we're only reading from the database
+      # and not modifying it. We're also on the same connection pool as ActiveRecord::Base.
+      # The dump process also runs standalone, so we don't need to worry about the connection being
+      # used elsewhere.
+      Timescaledb.use_connection @connection.raw_connection
+
+      Timescaledb.extension.installed? && Timescaledb.hypertables.any?
     end
 
     # Ignores Timescale related schemas when dumping the schema

spec/timescaledb/connection_spec.rb

@@ -0,0 +1,39 @@
+RSpec.describe Timescaledb do
+  describe '.establish_connection' do
+    it 'returns a PG::Connection object' do
+      expect do
+         Timescaledb.establish_connection(ENV['PG_URI_TEST'])
+      end.to_not raise_error
+    end
+  end
+
+  describe ::Timescaledb::Connection do
+    subject(:connection) { Timescaledb::Connection.instance }
+
+    it 'returns a Connection object' do
+      is_expected.to be_a(Timescaledb::Connection)
+    end
+
+    it 'has fast access to the connection' do
+      expect(connection.send(:connection)).to be_a(PG::Connection)
+    end
+
+    describe '#connected?' do
+      it {  expect(connection.connected?).to be_truthy }
+    end
+
+    describe '#query_first' do
+      let(:sql) { "select 1 as one" }
+      subject(:result) { connection.query_first(sql) }
+
+      it { expect(result).to be_a(OpenStruct) }
+    end
+
+    describe '#query' do
+      let(:sql) { "select 1 as one" }
+      subject(:result) { connection.query(sql) }
+
+      it { expect(result).to eq([OpenStruct.new({"one" => "1"})]) }
+    end
+  end
+end

spec/timescaledb_spec.rb

@@ -3,6 +3,16 @@
     expect(Timescaledb::VERSION).not_to be nil
   end
 
+  describe ".extension" do
+    describe ".installed?" do
+      it { expect(Timescaledb.extension.installed?).to be_truthy }
+    end
+
+    describe ".version" do
+      it { expect(Timescaledb.extension.version).not_to be_empty }
+    end
+  end
+
   describe ".chunks" do
     subject { Timescaledb.chunks }