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]

2 files changed, 20 insertions, 5 deletions

diff --git a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
index c85ea8e1da..79dc98607a 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb
@@ -1064,8 +1064,8 @@ module ActiveRecord
         options
       end
 
-      def dump_schema_information #:nodoc:
-        versions = ActiveRecord::SchemaMigration.all_versions
+      def dump_schema_information # :nodoc:
+        versions = schema_migration.all_versions
         insert_versions_sql(versions) if versions.any?
       end
 
@@ -1081,7 +1081,7 @@ module ActiveRecord
         end
 
         version = version.to_i
-        sm_table = quote_table_name(ActiveRecord::SchemaMigration.table_name)
+        sm_table = quote_table_name(schema_migration.table_name)
 
         migrated = migration_context.get_all_versions
         versions = migration_context.migrations.map(&:version)
@@ -1454,7 +1454,7 @@ module ActiveRecord
         end
 
         def insert_versions_sql(versions)
-          sm_table = quote_table_name(ActiveRecord::SchemaMigration.table_name)
+          sm_table = quote_table_name(schema_migration.table_name)
 
           if versions.is_a?(Array)
             sql = +"INSERT INTO #{sm_table} (version) VALUES\n"
diff --git a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
index cfd986ebf9..7d3ec7ecfd 100644
--- a/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
+++ b/activerecord/lib/active_record/connection_adapters/abstract_adapter.rb
@@ -163,7 +163,22 @@ module ActiveRecord
       end
 
       def migration_context # :nodoc:
-        MigrationContext.new(migrations_paths)
+        MigrationContext.new(migrations_paths, schema_migration)
+      end
+
+      def schema_migration # :nodoc:
+        @schema_migration ||= begin
+                                conn = self
+                                spec_name = conn.pool.spec.name
+                                name = "#{spec_name}::SchemaMigration"
+
+                                Class.new(ActiveRecord::SchemaMigration) do
+                                  define_singleton_method(:name) { name }
+                                  define_singleton_method(:to_s) { name }
+
+                                  self.connection_specification_name = spec_name
+                                end
+                              end
       end
 
       class Version