MONGOID-4901 Add sandbox mode (#5523)

Author: comandeo-mongo

lib/mongoid/railtie.rb

@@ -9,6 +9,13 @@ module Mongoid
     # Hooks Mongoid into Rails 3 and higher.
     class Railtie < Rails::Railtie
 
+      console do |app|
+        if app.sandbox?
+          require "mongoid/railties/console_sandbox"
+          start_sandbox
+        end
+      end
+
       # Mapping of rescued exceptions to HTTP responses
       #
       # @example

lib/mongoid/railties/console_sandbox.rb

@@ -0,0 +1,41 @@
+require "mongoid/threaded"
+require "mongoid/errors/transactions_not_supported"
+
+# This method raises an error if the cluster the client is connected to
+# does not support transactions in any case. At the moment this is the case
+# of the standalone topology.
+#
+# Please note that if this method did not raise, it does not guarantee that
+# transactions are available for the cluster.
+#
+# @param [ Mongo::Client ] client Client connected to a cluster to be tested.
+#
+# @raise [ Mongoid::Errors::TransactionsNotSupported ] If the cluster
+#   definitely does not support transactions.
+def check_if_transactions_might_be_available!(client)
+  if client.cluster.single?
+    raise Mongoid::Errors::TransactionsNotSupported
+  end
+end
+
+# Starts a transaction that should include all the operations inside
+# the sandboxed console session. This transaction should not be ever committed.
+# When a user end the console session, the client will disconnect, and
+# the transaction will be automatically aborted therefore.
+#
+# @param [ Mongo::Client ] client Client to start the transaction.
+def start_sandbox_transaction(client)
+  session = client.start_session
+  ::Mongoid::Threaded.set_session(session, client: client)
+  session.start_transaction
+end
+
+# Prepares console sandbox mode. This method should be called when
+# a user starts rails console with '--sandbox' flag.
+def start_sandbox
+  Mongoid.persistence_context.client.tap do |client|
+    check_if_transactions_might_be_available!(client)
+    start_sandbox_transaction(client)
+  end
+end
+

spec/mongoid/railties/console_sandbox_spec.rb

@@ -0,0 +1,43 @@
+require 'spec_helper'
+require 'mongoid/railties/console_sandbox'
+
+describe 'console_sandbox' do
+  describe '#check_if_transactions_might_be_available!' do
+    context 'cluster may support transactions' do
+      require_topology :replica_set, :sharded, :load_balanced
+
+      it 'does not raise' do
+        expect do
+          check_if_transactions_might_be_available!(Mongoid.default_client)
+        end.not_to raise_error
+      end
+    end
+
+    context 'cluster does not support transactions' do
+      require_topology :single
+
+      it 'raises an error' do
+        expect do
+          check_if_transactions_might_be_available!(Mongoid.default_client)
+        end.to raise_error(Mongoid::Errors::TransactionsNotSupported)
+      end
+    end
+  end
+
+  describe '#start_sandbox_transaction' do
+    require_transaction_support
+
+    before do
+      start_sandbox_transaction(Mongoid.default_client)
+    end
+
+    after do
+      Mongoid.send(:_session).abort_transaction
+      Mongoid::Threaded.clear_session(client: Mongoid.default_client)
+    end
+
+    it 'starts transaction' do
+      expect(Mongoid.send(:_session)).to be_in_transaction
+    end
+  end
+end