Dump the schema or structure of a database when calling db:migrate:name

activerecord/CHANGELOG.md

+*   Dump the schema or structure of a database when calling db:migrate:name
+
+    In previous versions of Rails, `rails db:migrate` would dump the schema of the database. In Rails 6, that holds true (`rails db:migrate` dumps all databases' schemas), but `rails db:migrate:name` does not share that behavior.
+
+    Going forward, calls to `rails db:migrate:name` will dump the schema (or structure) of the database being migrated.
+
+    *Kyle Thompson*
+
 *   Reset the `ActiveRecord::Base` connection after `rails db:migrate:name`
 
     When `rails db:migrate` has finished, it ensures the `ActiveRecord::Base` connection is reset to its original configuration. Going forward, `rails db:migrate:name` will have the same behavior.

activerecord/lib/active_record/railties/databases.rake

@@ -106,6 +106,25 @@ db_namespace = namespace :db do
     db_namespace["_dump"].reenable
   end
 
+  namespace :_dump do
+    ActiveRecord::Tasks::DatabaseTasks.for_each(databases) do |name|
+      # IMPORTANT: This task won't dump the schema if ActiveRecord::Base.dump_schema_after_migration is set to false
+      task name do
+        if ActiveRecord::Base.dump_schema_after_migration
+          case ActiveRecord::Base.schema_format
+          when :ruby then db_namespace["schema:dump:#{name}"].invoke
+          when :sql  then db_namespace["structure:dump:#{name}"].invoke
+          else
+            raise "unknown schema format #{ActiveRecord::Base.schema_format}"
+          end
+        end
+        # Allow this task to be called as many times as required. An example is the
+        # migrate:redo task, which calls other two internally that depend on this one.
+        db_namespace["_dump:#{name}"].reenable
+      end
+    end
+  end
+
   namespace :migrate do
     ActiveRecord::Tasks::DatabaseTasks.for_each(databases) do |name|
       desc "Migrate #{name} database for current environment"
@@ -114,6 +133,7 @@ db_namespace = namespace :db do
         db_config = ActiveRecord::Base.configurations.configs_for(env_name: Rails.env, name: name)
         ActiveRecord::Base.establish_connection(db_config)
         ActiveRecord::Tasks::DatabaseTasks.migrate
+        db_namespace["_dump:#{name}"].invoke
       ensure
         ActiveRecord::Base.establish_connection(original_db_config)
       end

railties/test/application/rake/multi_dbs_test.rb

@@ -154,6 +154,44 @@ def db_migrate_and_schema_dump_and_load_one_database(format, database)
         end
       end
 
+      def db_migrate_name_dumps_the_schema(name, schema_format)
+        add_to_config "config.active_record.schema_format = :#{schema_format}"
+        require "#{app_path}/config/environment"
+
+        Dir.chdir(app_path) do
+          generate_models_for_animals
+
+          assert_not(File.exist?("db/schema.rb"))
+          assert_not(File.exist?("db/animals_schema.rb"))
+          assert_not(File.exist?("db/structure.sql"))
+          assert_not(File.exist?("db/animals_structure.sql"))
+
+          rails("db:migrate:#{name}")
+
+          if schema_format == "ruby"
+            if name == "primary"
+              schema_dump = File.read("db/schema.rb")
+              assert_not(File.exist?("db/animals_schema.rb"))
+              assert_match(/create_table \"books\"/, schema_dump)
+            else
+              assert_not(File.exist?("db/schema.rb"))
+              schema_dump_animals = File.read("db/animals_schema.rb")
+              assert_match(/create_table \"dogs\"/, schema_dump_animals)
+            end
+          else
+            if name == "primary"
+              schema_dump = File.read("db/structure.sql")
+              assert_not(File.exist?("db/animals_structure.sql"))
+              assert_match(/CREATE TABLE (?:IF NOT EXISTS )?\"books\"/, schema_dump)
+            else
+              assert_not(File.exist?("db/structure.sql"))
+              schema_dump_animals = File.read("db/animals_structure.sql")
+              assert_match(/CREATE TABLE (?:IF NOT EXISTS )?\"dogs\"/, schema_dump_animals)
+            end
+          end
+        end
+      end
+
       def db_test_prepare_name(name, schema_format)
         add_to_config "config.active_record.schema_format = :#{schema_format}"
         require "#{app_path}/config/environment"
@@ -354,6 +392,23 @@ def generate_models_for_animals
         db_migrate_and_schema_dump_and_load "structure"
       end
 
+
+      test "db:migrate:name dumps the schema for the primary database" do
+        db_migrate_name_dumps_the_schema("primary", "ruby")
+      end
+
+      test "db:migrate:name dumps the schema for the animals database" do
+        db_migrate_name_dumps_the_schema("animals", "ruby")
+      end
+
+      test "db:migrate:name dumps the structure for the primary database" do
+        db_migrate_name_dumps_the_schema("primary", "sql")
+      end
+
+      test "db:migrate:name dumps the structure for the animals database" do
+        db_migrate_name_dumps_the_schema("animals", "sql")
+      end
+
       test "db:migrate:name and db:schema:dump:name and db:schema:load:name works for the primary database" do
         require "#{app_path}/config/environment"
         db_migrate_and_schema_dump_and_load_one_database("schema", "primary")