Move SchemaMigration to an independent object

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Move `ActiveRecord::SchemaMigration` to an independent object.
+
+    `ActiveRecord::SchemaMigration` no longer inherits from `ActiveRecord::Base` and is now an independent object that should be instantiated with a `connection`. This class is private and should not be used by applications directly. If you want to interact with the schema migrations table, please access it on the connection directly, for example: `ActiveRecord::Base.connection.schema_migration`.
+
+    *Eileen M. Uchitelle*
+
 *   Deprecate `all_connection_pools` and make `connection_pool_list` more explicit.
 
     Following on #45924 `all_connection_pools` is now deprecated. `connection_pool_list` will either take an explicit role or applications can opt into the new behavior by passing `:all`.

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -1270,7 +1270,7 @@ def check_constraint_exists?(table_name, **options)
       end
 
       def dump_schema_information # :nodoc:
-        versions = schema_migration.all_versions
+        versions = schema_migration.versions
         insert_versions_sql(versions) if versions.any?
       end
 

activerecord/lib/active_record/connection_adapters/abstract_adapter.rb

@@ -193,21 +193,7 @@ def migration_context # :nodoc:
       end
 
       def schema_migration # :nodoc:
-        @schema_migration ||= begin
-                                conn = self
-                                connection_name = conn.pool.pool_config.connection_name
-
-                                return ActiveRecord::SchemaMigration if connection_name == "ActiveRecord::Base"
-
-                                schema_migration_name = "#{connection_name}::SchemaMigration"
-
-                                Class.new(ActiveRecord::SchemaMigration) do
-                                  define_singleton_method(:name) { schema_migration_name }
-                                  define_singleton_method(:to_s) { schema_migration_name }
-
-                                  self.connection_specification_name = connection_name
-                                end
-                              end
+        SchemaMigration.new(self)
       end
 
       def internal_metadata # :nodoc:

activerecord/lib/active_record/migration.rb

@@ -950,14 +950,13 @@ def method_missing(method, *arguments, &block)
 
     def copy(destination, sources, options = {})
       copied = []
-      schema_migration = options[:schema_migration] || ActiveRecord::SchemaMigration
 
       FileUtils.mkdir_p(destination) unless File.exist?(destination)
 
-      destination_migrations = ActiveRecord::MigrationContext.new(destination, schema_migration).migrations
+      destination_migrations = ActiveRecord::MigrationContext.new(destination, SchemaMigration::NullSchemaMigration.new).migrations
       last = destination_migrations.last
       sources.each do |scope, path|
-        source_migrations = ActiveRecord::MigrationContext.new(path, schema_migration).migrations
+        source_migrations = ActiveRecord::MigrationContext.new(path, SchemaMigration::NullSchemaMigration.new).migrations
 
         source_migrations.each do |migration|
           source = File.binread(migration.filename)
@@ -1018,7 +1017,7 @@ def next_migration_number(number)
       if ActiveRecord.timestamped_migrations
         [Time.now.utc.strftime("%Y%m%d%H%M%S"), "%.14d" % number].max
       else
-        SchemaMigration.normalize_migration_number(number)
+        "%.3d" % number.to_i
       end
     end
 
@@ -1076,15 +1075,21 @@ def load_migration
   #
   # A migration context requires the path to the migrations is set
   # in the +migrations_paths+ parameter. Optionally a +schema_migration+
-  # class can be provided. For most applications, +SchemaMigration+ is
-  # sufficient. Multiple database applications need a +SchemaMigration+
-  # per primary database.
+  # class can be provided. Multiple database applications will instantiate
+  # a +SchemaMigration+ object per database. From the Rake tasks, Rails will
+  # handle this for you.
   class MigrationContext
     attr_reader :migrations_paths, :schema_migration, :internal_metadata
 
-    def initialize(migrations_paths, schema_migration = SchemaMigration, internal_metadata = InternalMetadata)
+    def initialize(migrations_paths, schema_migration = nil, internal_metadata = InternalMetadata)
+      if schema_migration == SchemaMigration
+        schema_migration = SchemaMigration.new(ActiveRecord::Base.connection)
+
+        ActiveSupport::Deprecation.warn("SchemaMigration no longer inherits from ActiveRecord::Base. Please instaniate a new SchemaMigration object with the desired connection, ie `ActiveRecord::SchemaMigration.new(ActiveRecord::Base.connection)`.")
+      end
+
       @migrations_paths = migrations_paths
-      @schema_migration = schema_migration
+      @schema_migration = schema_migration || SchemaMigration.new(ActiveRecord::Base.connection)
       @internal_metadata = internal_metadata
     end
 
@@ -1152,7 +1157,7 @@ def open # :nodoc:
 
     def get_all_versions # :nodoc:
       if schema_migration.table_exists?
-        schema_migration.all_versions.map(&:to_i)
+        schema_migration.integer_versions
       else
         []
       end
@@ -1257,7 +1262,9 @@ class << self
 
       # For cases where a table doesn't exist like loading from schema cache
       def current_version
-        MigrationContext.new(migrations_paths, SchemaMigration, InternalMetadata).current_version
+        schema_migration = SchemaMigration.new(ActiveRecord::Base.connection)
+
+        MigrationContext.new(migrations_paths, schema_migration, InternalMetadata).current_version
       end
     end
 
@@ -1327,7 +1334,7 @@ def migrated
     end
 
     def load_migrated
-      @migrated_versions = Set.new(@schema_migration.all_versions.map(&:to_i))
+      @migrated_versions = Set.new(@schema_migration.integer_versions)
     end
 
     private
@@ -1406,10 +1413,10 @@ def validate(migrations)
       def record_version_state_after_migrating(version)
         if down?
           migrated.delete(version)
-          @schema_migration.delete_by(version: version.to_s)
+          @schema_migration.delete_version(version.to_s)
         else
           migrated << version
-          @schema_migration.create!(version: version.to_s)
+          @schema_migration.create_version(version.to_s)
         end
       end
 

activerecord/lib/active_record/schema_migration.rb

@@ -1,54 +1,87 @@
 # frozen_string_literal: true
 
-require "active_record/scoping/default"
-require "active_record/scoping/named"
-
 module ActiveRecord
   # This class is used to create a table that keeps track of which migrations
   # have been applied to a given database. When a migration is run, its schema
-  # number is inserted in to the `SchemaMigration.table_name` so it doesn't need
+  # number is inserted in to the schema migrations table so it doesn't need
   # to be executed the next time.
-  class SchemaMigration < ActiveRecord::Base # :nodoc:
-    class << self
-      def primary_key
-        "version"
-      end
+  class SchemaMigration # :nodoc:
+    attr_reader :connection, :arel_table
+
+    def initialize(connection)
+      @connection = connection
+      @arel_table = Arel::Table.new(table_name)
+    end
+
+    def create_version(version)
+      im = Arel::InsertManager.new(arel_table)
+      im.insert(arel_table[primary_key] => version)
+      connection.insert(im, "#{self} Create", primary_key, version)
+    end
+
+    def delete_version(version)
+      dm = Arel::DeleteManager.new(arel_table)
+      dm.wheres = [arel_table[primary_key].eq(version)]
 
-      def table_name
-        "#{table_name_prefix}#{schema_migrations_table_name}#{table_name_suffix}"
+      connection.delete(dm, "#{self} Destroy")
+    end
+
+    def delete_all_versions
+      versions.each do |version|
+        delete_version(version)
       end
+    end
+
+    def primary_key
+      "version"
+    end
+
+    def table_name
+      "#{ActiveRecord::Base.table_name_prefix}#{ActiveRecord::Base.schema_migrations_table_name}#{ActiveRecord::Base.table_name_suffix}"
+    end
 
-      def create_table
-        unless connection.table_exists?(table_name)
-          connection.create_table(table_name, id: false) do |t|
-            t.string :version, **connection.internal_string_options_for_primary_key
-          end
+    def create_table
+      unless connection.table_exists?(table_name)
+        connection.create_table(table_name, id: false) do |t|
+          t.string :version, **connection.internal_string_options_for_primary_key
         end
       end
+    end
 
-      def drop_table
-        connection.drop_table table_name, if_exists: true
-      end
+    def drop_table
+      connection.drop_table table_name, if_exists: true
+    end
 
-      def normalize_migration_number(number)
-        "%.3d" % number.to_i
-      end
+    def normalize_migration_number(number)
+      "%.3d" % number.to_i
+    end
 
-      def normalized_versions
-        all_versions.map { |v| normalize_migration_number v }
-      end
+    def normalized_versions
+      versions.map { |v| normalize_migration_number v }
+    end
 
-      def all_versions
-        order(:version).pluck(:version)
-      end
+    def versions
+      sm = Arel::SelectManager.new(arel_table)
+      sm.project(arel_table[primary_key])
+      sm.order(arel_table[primary_key].asc)
+      connection.select_values(sm)
+    end
 
-      def table_exists?
-        connection.data_source_exists?(table_name)
-      end
+    def integer_versions
+      versions.map(&:to_i)
+    end
+
+    def count
+      sm = Arel::SelectManager.new(arel_table)
+      sm.project(*Arel::Nodes::Count.new([Arel.star]))
+      connection.select_values(sm).first
+    end
+
+    def table_exists?
+      connection.data_source_exists?(table_name)
     end
 
-    def version
-      super.to_i
+    class NullSchemaMigration
     end
   end
 end

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -192,7 +192,7 @@ def prepare_all
           ActiveRecord::Base.establish_connection(db_config)
 
           begin
-            database_initialized = ActiveRecord::SchemaMigration.table_exists?
+            database_initialized = ActiveRecord::Base.connection.schema_migration.table_exists?
           rescue ActiveRecord::NoDatabaseError
             create(db_config)
             retry

activerecord/test/cases/active_record_schema_test.rb

@@ -20,7 +20,7 @@ class ActiveRecordSchemaTest < ActiveRecord::TestCase
     @connection.drop_table :nep_schema_migrations rescue nil
     @connection.drop_table :has_timestamps rescue nil
     @connection.drop_table :multiple_indexes rescue nil
-    @schema_migration.delete_all rescue nil
+    @schema_migration.delete_all_versions rescue nil
     ActiveRecord::Migration.verbose = @original_verbose
   end
 
@@ -31,7 +31,7 @@ def test_has_primary_key
 
     @schema_migration.create_table
     assert_difference "@schema_migration.count", 1 do
-      @schema_migration.create version: 12
+      @schema_migration.create_version(12)
     end
   ensure
     @schema_migration.drop_table
@@ -69,7 +69,6 @@ def test_schema_define
   def test_schema_define_with_table_name_prefix
     old_table_name_prefix = ActiveRecord::Base.table_name_prefix
     ActiveRecord::Base.table_name_prefix = "nep_"
-    @schema_migration.reset_table_name
     @internal_metadata.reset_table_name
     ActiveRecord::Schema.define(version: 7) do
       create_table :fruits do |t|
@@ -82,7 +81,6 @@ def test_schema_define_with_table_name_prefix
     assert_equal 7, @connection.migration_context.current_version
   ensure
     ActiveRecord::Base.table_name_prefix = old_table_name_prefix
-    @schema_migration.reset_table_name
     @internal_metadata.reset_table_name
   end
 

activerecord/test/cases/adapters/mysql2/schema_migrations_test.rb

@@ -5,6 +5,10 @@
 class SchemaMigrationsTest < ActiveRecord::Mysql2TestCase
   self.use_transactional_tests = false
 
+  def setup
+    @schema_migration = ActiveRecord::Base.connection.schema_migration
+  end
+
   def test_renaming_index_on_foreign_key
     connection.add_index "engines", "car_id"
     connection.add_foreign_key :engines, :cars, name: "fk_engines_cars"
@@ -17,10 +21,10 @@ def test_renaming_index_on_foreign_key
 
   def test_initializes_schema_migrations_for_encoding_utf8mb4
     with_encoding_utf8mb4 do
-      table_name = ActiveRecord::SchemaMigration.table_name
+      table_name = @schema_migration.table_name
       connection.drop_table table_name, if_exists: true
 
-      ActiveRecord::SchemaMigration.create_table
+      @schema_migration.create_table
 
       assert connection.column_exists?(table_name, :version, :string)
     end

activerecord/test/cases/adapters/mysql2/table_options_test.rb

@@ -94,7 +94,7 @@ def teardown
     ActiveRecord::Base.logger       = @logger_was
     ActiveRecord::Migration.verbose = @verbose_was
     ActiveRecord::Base.connection.drop_table "mysql_table_options", if_exists: true
-    ActiveRecord::SchemaMigration.delete_all rescue nil
+    ActiveRecord::Base.connection.schema_migration.delete_all_versions rescue nil
   end
 
   test "new migrations do not contain default ENGINE=InnoDB option" do

activerecord/test/cases/adapters/postgresql/extension_migration_test.rb

@@ -27,20 +27,18 @@ def setup
 
     ActiveRecord::Base.table_name_prefix = "p_"
     ActiveRecord::Base.table_name_suffix = "_s"
-    @connection.schema_migration.reset_table_name
     @connection.internal_metadata.reset_table_name
 
-    @connection.schema_migration.delete_all rescue nil
+    @connection.schema_migration.delete_all_versions rescue nil
     ActiveRecord::Migration.verbose = false
   end
 
   def teardown
-    @connection.schema_migration.delete_all rescue nil
+    @connection.schema_migration.delete_all_versions rescue nil
     ActiveRecord::Migration.verbose = true
 
     ActiveRecord::Base.table_name_prefix = @old_table_name_prefix
     ActiveRecord::Base.table_name_suffix = @old_table_name_suffix
-    @connection.schema_migration.reset_table_name
     @connection.internal_metadata.reset_table_name
 
     super

activerecord/test/cases/adapters/postgresql/uuid_test.rb

@@ -308,7 +308,7 @@ def migrate(x)
   ensure
     drop_table "pg_uuids_4"
     ActiveRecord::Migration.verbose = @verbose_was
-    ActiveRecord::Base.connection.schema_migration.delete_all
+    ActiveRecord::Base.connection.schema_migration.delete_all_versions
   end
   uses_transaction :test_schema_dumper_for_uuid_primary_key_default_in_legacy_migration
 end
@@ -360,7 +360,7 @@ def migrate(x)
   ensure
     drop_table "pg_uuids_4"
     ActiveRecord::Migration.verbose = @verbose_was
-    ActiveRecord::Base.connection.schema_migration.delete_all
+    ActiveRecord::Base.connection.schema_migration.delete_all_versions
   end
   uses_transaction :test_schema_dumper_for_uuid_primary_key_with_default_nil_in_legacy_migration
 end