From bbbe7c0913c269e1889e9b8165b1a08b5eb7372b Mon Sep 17 00:00:00 2001
From: Andrew Novoselac <andrew.novoselac@shopify.com>
Date: Sat, 7 Sep 2024 18:39:40 -0400
Subject: [PATCH] When running db:migrate on a fresh database, load the
 database schema before running migrations.

If we have an existing schema file and we run db:migrate before setting up the database, we will not load the schema before running migrations, so when we dump the schema will overwrite the existing schema file and lose the tables define there. Instead, we should check if the db is setup and if it is not lload the schema, before running migrations.
---
 activerecord/CHANGELOG.md                     |  4 +++
 .../lib/active_record/tasks/database_tasks.rb | 36 ++++++++++++-------
 railties/test/application/rake/dbs_test.rb    | 13 +++++++
 3 files changed, 40 insertions(+), 13 deletions(-)

diff --git a/activerecord/CHANGELOG.md b/activerecord/CHANGELOG.md
index f187835bb0ae3..82949dde4891a 100644
--- a/activerecord/CHANGELOG.md
+++ b/activerecord/CHANGELOG.md
@@ -1,3 +1,7 @@
+*   When running `db:migrate` on a fresh database, load the database schema before running migrations.
+
+    *Andrew Novoselac*
+
 *   Deprecate `unsigned_float` and `unsigned_decimal` short-hand column methods.
 
     As of MySQL 8.0.17, the UNSIGNED attribute is deprecated for columns of type FLOAT, DOUBLE,
diff --git a/activerecord/lib/active_record/tasks/database_tasks.rb b/activerecord/lib/active_record/tasks/database_tasks.rb
index 9fadc7184b594..a9cafeb641c82 100644
--- a/activerecord/lib/active_record/tasks/database_tasks.rb
+++ b/activerecord/lib/active_record/tasks/database_tasks.rb
@@ -179,20 +179,9 @@ def prepare_all
 
         each_current_configuration(env) do |db_config|
           with_temporary_pool(db_config) do
-            begin
-              database_initialized = migration_connection_pool.schema_migration.table_exists?
-            rescue ActiveRecord::NoDatabaseError
-              create(db_config)
-              retry
-            end
+            database_initialized = initialize_database(db_config)
 
-            unless database_initialized
-              if File.exist?(schema_dump_path(db_config))
-                load_schema(db_config, ActiveRecord.schema_format, nil)
-              end
-
-              seed = true
-            end
+            seed = true if database_initialized
           end
         end
 
@@ -259,6 +248,8 @@ def migrate(version = nil)
 
         check_target_version
 
+        initialize_database(migration_connection_pool.db_config)
+
         migration_connection_pool.migration_context.migrate(target_version) do |migration|
           if version.blank?
             scope.blank? || scope == migration.scope
@@ -667,6 +658,25 @@ def check_current_protected_environment!(db_config)
           rescue ActiveRecord::NoDatabaseError
           end
         end
+
+        def initialize_database(db_config)
+          with_temporary_pool(db_config) do
+            begin
+              database_already_initialized = migration_connection_pool.schema_migration.table_exists?
+            rescue ActiveRecord::NoDatabaseError
+              create(db_config)
+              retry
+            end
+
+            unless database_already_initialized
+              if File.exist?(schema_dump_path(db_config))
+                load_schema(db_config, ActiveRecord.schema_format, nil)
+              end
+            end
+
+            !database_already_initialized
+          end
+        end
     end
   end
 end
diff --git a/railties/test/application/rake/dbs_test.rb b/railties/test/application/rake/dbs_test.rb
index f99980fceba39..8b9d3cb83ff12 100644
--- a/railties/test/application/rake/dbs_test.rb
+++ b/railties/test/application/rake/dbs_test.rb
@@ -350,6 +350,19 @@ def db_migrate_and_status(expected_database)
         db_migrate_and_status database_url_db_name
       end
 
+      test "db:migrate on new db loads schema" do
+        app_file "db/schema.rb", <<-RUBY
+          ActiveRecord::Schema.define(version: 20140423102712) do
+            create_table(:comments) {}
+          end
+        RUBY
+
+        rails "db:migrate"
+        list_tables = lambda { rails("runner", "p ActiveRecord::Base.lease_connection.tables.sort").strip }
+
+        assert_equal "[\"ar_internal_metadata\", \"comments\", \"schema_migrations\"]", list_tables[]
+      end
+
       def db_schema_dump
         Dir.chdir(app_path) do
           args = ["generate", "model", "book", "title:string"]