Implement db config option `database_tasks: false`

activerecord/CHANGELOG.md

@@ -1,3 +1,24 @@
+*   Add database config option `database_tasks`
+
+    If you would like to connect to an external database without any database
+    mangement tasks such as schema management, migrations, seeds, etc. you can set
+    the per database config option `database_tasks: false`
+
+    ```yaml
+    # config/database.yml
+
+    production:
+      primary:
+        database: my_database
+        adapter: mysql2
+      animals:
+        database: my_animals_database
+        adapter: mysql2
+        database_tasks: false
+    ```
+
+    *Weston Ganger*
+
 *   Fix `ActiveRecord::InternalMetadata` to not be broken by `config.active_record.record_timestamps = false`
 
     Since the model always create the timestamp columns, it has to set them, otherwise it breaks

activerecord/lib/active_record/database_configurations.rb

@@ -48,7 +48,7 @@ module ActiveRecord
 
       unless include_replicas
         configs = configs.select do |db_config|
-          !db_config.replica?
+          db_config.database_tasks?
         end
       end
 

activerecord/lib/active_record/database_configurations/hash_config.rb

@@ -113,6 +113,10 @@ module ActiveRecord
       def schema_dump
         configuration_hash.fetch(:schema_dump, true)
       end
+
+      def database_tasks? # :nodoc:
+        !replica? && !!configuration_hash.fetch(:database_tasks, true)
+      end
     end
   end
 end

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -178,6 +178,8 @@ module ActiveRecord
         return if database_configs.count == 1
 
         database_configs.each do |db_config|
+          next unless db_config.database_tasks?
+
           yield db_config.name
         end
       end

activerecord/test/cases/database_configurations/hash_config_test.rb

@@ -122,6 +122,19 @@ module ActiveRecord
         config = HashConfig.new("default_env", "primary", { schema_dump: false })
         assert_equal false, config.schema_dump
       end
+
+      def test_database_tasks_defaults_to_true
+        config = HashConfig.new("default_env", "primary", {})
+        assert_equal true, config.database_tasks?
+      end
+
+      def test_database_tasks_overrides_with_value
+        config = HashConfig.new("default_env", "primary", database_tasks: false)
+        assert_equal false, config.database_tasks?
+
+        config = HashConfig.new("default_env", "primary", database_tasks: "str")
+        assert_equal true, config.database_tasks?
+      end
     end
   end
 end

guides/source/active_record_multiple_databases.md

@@ -202,6 +202,24 @@ Note that there is no command for creating the database users, and you'll need t
 to support the readonly users for your replicas. If you want to create just the animals
 database you can run `bin/rails db:create:animals`.
 
+## Connecting to Databases without Managing Schema and Migrations
+
+If you would like to connect to an external database without any database
+mangement tasks such as schema management, migrations, seeds, etc. you can set
+the per database config option `database_tasks: false`. By default it is
+set to true.
+
+```yaml
+production:
+  primary:
+    database: my_database
+    adapter: mysql2
+  animals:
+    database: my_animals_database
+    adapter: mysql2
+    database_tasks: false
+```
+
 ## Generators and Migrations
 
 Migrations for multiple databases should live in their own folders prefixed with the

railties/test/application/rake/multi_dbs_test.rb

@@ -1065,6 +1065,45 @@ module ApplicationTests
 
         db_migrate_and_schema_dump_and_load
       end
+
+      test "when database_tasks is false, then do not run the database tasks on that db" do
+        app_file "config/database.yml", <<-YAML
+          development:
+            primary:
+              database: db/default.sqlite3
+              adapter: sqlite3
+            animals:
+              database: db/development_animals.sqlite3
+              adapter: sqlite3
+              database_tasks: false
+              schema_dump: true ### database_tasks should override all sub-settings
+        YAML
+
+        Dir.chdir(app_path) do
+          animals_db_exists = lambda{ rails("runner", "puts !!(AnimalsBase.connection rescue false)").strip }
+
+          generate_models_for_animals
+
+          assert_equal "true", animals_db_exists.call
+
+          assert_not File.exist?("db/animals_schema.yml")
+
+          begin
+            assert_raise RuntimeError do
+              rails "db:migrate:animals" ### Task not defined
+            end
+          rescue RuntimeError => e
+            assert_includes e.message, "See the list of available tasks"
+          end
+
+          rails "db:schema:dump"
+          assert_not File.exist?("db/animals_schema.yml")
+
+          rails "db:drop"
+          assert_equal "true", animals_db_exists.call
+        end
+      end
+
     end
   end
 end