Move SchemaMigration to migration_context

This PR moves the `schema_migration` to `migration_context` so that we
can access the `schema_migration` per connection.

This does not change behavior of the SchemaMigration if you are using
one database. This also does not change behavior of any public APIs.
`Migrator` is private as is `MigrationContext` so we can change these as
needed.

We now need to pass a `schema_migration` to `Migrator` so that we can
run migrations on the right connection outside the context of a rake
task.

The bugs this fixes were discovered while debugging the issues around
the SchemaCache on initialization with multiple database. It was clear
that `get_all_versions` wouldn't work without these changes outside the
context of a rake task (because in the rake task we establish a
connection and change AR::Base.connection to the db we're running on).

Because the `SchemaCache` relies on the `SchemaMigration` information we
need to make sure we store it per-connection rather than on
ActiveRecord::Base.

[Eileen M. Uchitelle & Aaron Patterson]

1 files changed, 4 insertions, 4 deletions

diff --git a/activerecord/test/cases/adapters/postgresql/uuid_test.rb b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
index 2be67aae20..a1c985fc71 100644
--- a/activerecord/test/cases/adapters/postgresql/uuid_test.rb
+++ b/activerecord/test/cases/adapters/postgresql/uuid_test.rb
@@ -293,14 +293,14 @@ class PostgresqlUUIDGenerationTest < ActiveRecord::PostgreSQLTestCase
         create_table("pg_uuids_4", id: :uuid)
       end
     end.new
-    ActiveRecord::Migrator.new(:up, [migration]).migrate
+    ActiveRecord::Migrator.new(:up, [migration], ActiveRecord::Base.connection.schema_migration).migrate
 
     schema = dump_table_schema "pg_uuids_4"
     assert_match(/\bcreate_table "pg_uuids_4", id: :uuid, default: -> { "uuid_generate_v4\(\)" }/, schema)
   ensure
     drop_table "pg_uuids_4"
     ActiveRecord::Migration.verbose = @verbose_was
-    ActiveRecord::SchemaMigration.delete_all
+    ActiveRecord::Base.connection.schema_migration.delete_all
   end
   uses_transaction :test_schema_dumper_for_uuid_primary_key_default_in_legacy_migration
 end
@@ -343,14 +343,14 @@ class PostgresqlUUIDTestNilDefault < ActiveRecord::PostgreSQLTestCase
         create_table("pg_uuids_4", id: :uuid, default: nil)
       end
     end.new
-    ActiveRecord::Migrator.new(:up, [migration]).migrate
+    ActiveRecord::Migrator.new(:up, [migration], ActiveRecord::Base.connection.schema_migration).migrate
 
     schema = dump_table_schema "pg_uuids_4"
     assert_match(/\bcreate_table "pg_uuids_4", id: :uuid, default: nil/, schema)
   ensure
     drop_table "pg_uuids_4"
     ActiveRecord::Migration.verbose = @verbose_was
-    ActiveRecord::SchemaMigration.delete_all
+    ActiveRecord::Base.connection.schema_migration.delete_all
   end
   uses_transaction :test_schema_dumper_for_uuid_primary_key_with_default_nil_in_legacy_migration
 end