Fix schema cache load and corresponding test

This test was incorrect. `primary` was winning for the schema cache load
but when you boot an application it's actually the first configuration
that wins (in a multi db app).

The test didn't catch this because I forgot to add a migrations_paths to
the configuration.

We updated the schema cache loader railtie as well because any
application that didn't have a `primary` config would not be able to use
the schema cache. Originally we thought we'd enforce a `primary`
configuration but no longer feel that's correct. It's simpler to say
that the first wins in a 3-tier rather than implementing a solution to
require `primary` and / or allow aliases.
Co-authored-by: NJohn Crepezzi <john.crepezzi@gmail.com>
Co-authored-by: NJohn Hawthorn <john@hawthorn.email>

activerecord/lib/active_record/railtie.rb

@@ -129,13 +129,11 @@ class Railtie < Rails::Railtie # :nodoc:
       if config.active_record.delete(:use_schema_cache_dump)
         config.after_initialize do |app|
           ActiveSupport.on_load(:active_record) do
-            db_config = ActiveRecord::Base.configurations.configs_for(
-              env_name: Rails.env,
-              name: "primary",
-            )
+            db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env).first
+
             filename = ActiveRecord::Tasks::DatabaseTasks.cache_dump_filename(
-              "primary",
-              schema_cache_path: db_config&.schema_cache_path,
+              db_config.name,
+              schema_cache_path: db_config&.schema_cache_path
             )
 
             cache = ActiveRecord::ConnectionAdapters::SchemaCache.load_from(filename)

railties/test/application/rake/dbs_test.rb

@@ -343,11 +343,14 @@ def db_migrate_and_status(expected_database)
         db_migrate_and_status database_url_db_name
       end
 
-      def db_schema_dump
+      def db_schema_dump(database: nil)
         Dir.chdir(app_path) do
-          rails "generate", "model", "book", "title:string"
+          args = ["generate", "model", "book", "title:string"]
+          args << "--database=#{database}" if database
+          rails args
           rails "db:migrate", "db:schema:dump"
-          schema_dump = File.read("db/schema.rb")
+          dump_name = database ? "#{database}_schema.rb" : "schema.rb"
+          schema_dump = File.read("db/#{dump_name}")
           assert_match(/create_table \"books\"/, schema_dump)
         end
       end
@@ -412,7 +415,7 @@ def db_schema_cache_dump(filename = "db/schema_cache.yml")
         ENV["SCHEMA_CACHE"] = @old_schema_cache_env
       end
 
-      test "db:schema:cache:dump primary wins" do
+      test "db:schema:cache:dump first config wins" do
         Dir.chdir(app_path) do
           File.open("#{app_path}/config/database.yml", "w") do |f|
             f.puts <<-YAML
@@ -426,6 +429,7 @@ def db_schema_cache_dump(filename = "db/schema_cache.yml")
               some_entry:
                 <<: *default
                 database: db/development_other.sqlite3
+                migrations_paths: db/some_entry_migrate
               primary:
                 <<: *default
                 database: db/development.sqlite3
@@ -433,7 +437,7 @@ def db_schema_cache_dump(filename = "db/schema_cache.yml")
           end
         end
 
-        db_schema_dump
+        db_schema_dump(database: "some_entry")
         db_schema_cache_dump
       end