Merge pull request #38751 from nburns/metadata-table

check for metadata table support

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -111,6 +111,10 @@ def replica?
         @config[:replica] || false
       end
 
+      def use_metadata_table?
+        @config.fetch(:use_metadata_table, true)
+      end
+
       # Determines whether writes are currently being prevents.
       #
       # Returns true if the connection is a replica, or if +prevent_writes+

activerecord/lib/active_record/internal_metadata.rb

@@ -6,8 +6,15 @@
 module ActiveRecord
   # This class is used to create a table that keeps track of values and keys such
   # as which environment migrations were run in.
+  #
+  # This is enabled by default. To disable this functionality set
+  # `use_metadata_table` to false in your database configuration.
   class InternalMetadata < ActiveRecord::Base # :nodoc:
     class << self
+      def enabled?
+        ActiveRecord::Base.connection.use_metadata_table?
+      end
+
       def _internal?
         true
       end
@@ -21,15 +28,21 @@ def table_name
       end
 
       def []=(key, value)
+        return unless enabled?
+
         find_or_initialize_by(key: key).update!(value: value)
       end
 
       def [](key)
+        return unless enabled?
+
         where(key: key).pluck(:value).first
       end
 
       # Creates an internal metadata table with columns +key+ and +value+
       def create_table
+        return unless enabled?
+
         unless table_exists?
           key_options = connection.internal_string_options_for_primary_key
 
@@ -42,6 +55,8 @@ def create_table
       end
 
       def drop_table
+        return unless enabled?
+
         connection.drop_table table_name, if_exists: true
       end
     end

activerecord/lib/active_record/migration.rb

@@ -190,6 +190,14 @@ def initialize(current: nil, stored: nil)
     end
   end
 
+  class EnvironmentStorageError < ActiveRecordError # :nodoc:
+    def initialize
+      msg = +"You are attempting to store the environment in a database where metadata is disabled.\n"
+      msg << "Check your database configuration to see if this is intended."
+      super(msg)
+    end
+  end
+
   # = Active Record Migrations
   #
   # Migrations can manage the evolution of a schema used by several physical
@@ -1138,6 +1146,7 @@ def protected_environment?
     end
 
     def last_stored_environment
+      return nil unless ActiveRecord::InternalMetadata.enabled?
       return nil if current_version == 0
       raise NoEnvironmentInSchemaError unless ActiveRecord::InternalMetadata.table_exists?
 

activerecord/lib/active_record/railties/databases.rake

@@ -8,6 +8,7 @@ databases = ActiveRecord::Tasks::DatabaseTasks.setup_initial_database_yaml
 db_namespace = namespace :db do
   desc "Set the environment value for the database"
   task "environment:set" => :load_config do
+    raise ActiveRecord::EnvironmentStorageError unless ActiveRecord::InternalMetadata.enabled?
     ActiveRecord::InternalMetadata.create_table
     ActiveRecord::InternalMetadata[:environment] = ActiveRecord::Base.connection.migration_context.current_environment
   end

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -348,7 +348,10 @@ def schema_up_to_date?(configuration, format = ActiveRecord::Base.schema_format,
         return true unless File.exist?(file)
 
         ActiveRecord::Base.establish_connection(db_config)
+
+        return false unless ActiveRecord::InternalMetadata.enabled?
         return false unless ActiveRecord::InternalMetadata.table_exists?
+
         ActiveRecord::InternalMetadata[:schema_sha1] == schema_sha1(file)
       end
 

activerecord/test/cases/migration_test.rb

@@ -640,6 +640,29 @@ def test_internal_metadata_stores_environment_when_other_data_exists
     assert_equal "bar", ActiveRecord::InternalMetadata[:foo]
   end
 
+  def test_internal_metadata_not_used_when_not_enabled
+    ActiveRecord::InternalMetadata.drop_table
+    original_config = ActiveRecord::Base.connection.instance_variable_get("@config")
+
+    modified_config = original_config.dup.merge(use_metadata_table: false)
+
+    ActiveRecord::Base.connection
+      .instance_variable_set("@config", modified_config)
+
+    assert_not ActiveRecord::InternalMetadata.enabled?
+    assert_not ActiveRecord::InternalMetadata.table_exists?
+
+    migrations_path = MIGRATIONS_ROOT + "/valid"
+    migrator = ActiveRecord::MigrationContext.new(migrations_path, @schema_migration)
+    migrator.up
+
+    assert_not ActiveRecord::InternalMetadata[:environment]
+    assert_not ActiveRecord::InternalMetadata.table_exists?
+  ensure
+    ActiveRecord::Base.connection.instance_variable_set("@config", original_config)
+    ActiveRecord::InternalMetadata.create_table
+  end
+
   def test_proper_table_name_on_migration
     reminder_class = new_isolated_reminder_class
     migration = ActiveRecord::Migration.new

guides/source/configuring.md

@@ -1260,6 +1260,21 @@ development:
 
 Change the username and password in the `development` section as appropriate.
 
+#### Configuring Metadata Storage
+
+By default Rails will store information about your Rails environment and schema
+in an internal table named `ar_internal_metadata`.
+
+To turn this off per connection, set `use_metadata_table` in your database
+configuration. This is useful when working with a shared database and/or
+database user that cannot create tables.
+
+```yaml
+development:
+  adapter: postgresql
+  use_metadata_table: false
+```
+
 ### Creating Rails Environments
 
 By default Rails ships with three environments: "development", "test", and "production". While these are sufficient for most use cases, there are circumstances when you want more environments.