Rad*_*sky 84

答案很简单:从数据库中.

顺便说一下 - 当你查看db:*tasks(.../activerecord/railties/databases.rake)的源代码时,你可以看到迁移任务在运行后调用schema:dump

desc "Migrate the database (options: VERSION=x, VERBOSE=false)."
task :migrate => :environment do
  ActiveRecord::Migration.verbose = ENV["VERBOSE"] ? ENV["VERBOSE"] == "true" : true
  ActiveRecord::Migrator.migrate("db/migrate/", ENV["VERSION"] ? ENV["VERSION"].to_i : nil)
  Rake::Task["db:schema:dump"].invoke if ActiveRecord::Base.schema_format == :ruby
end
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因此,迁移的工作方式是更改数据库,然后生成schema.rb文件.