如何检查Rails迁移中的数据库类型? [英] How do I check the Database type in a Rails Migration?

问题描述

我进行了以下迁移，我希望能够检查与该环境相关的当前数据库是否是mysql数据库.如果是mysql，则我要执行特定于数据库的SQL.

I have the following migration and I want to be able to check if the current database related to the environment is a mysql database. If it's mysql then I want to execute the SQL that is specific to the database.

我该怎么办?

class AddUsersFb < ActiveRecord::Migration

  def self.up
    add_column :users, :fb_user_id, :integer
    add_column :users, :email_hash, :string
    #if mysql
    #execute("alter table users modify fb_user_id bigint")
  end

  def self.down
    remove_column :users, :fb_user_id
    remove_column :users, :email_hash
  end

end

推荐答案

ActiveRecord::Base.connection将为您提供有关boot.rb和environment.rb

ActiveRecord::Base.connection返回很多信息.因此，您必须确切了解要查找的内容.

ActiveRecord::Base.connection returns a lot of information. So you've got to know exactly what you're looking for.

马塞尔指出:

ActiveRecord::Base.connection.instance_of? 
  ActiveRecord::ConnectionAdapters::MysqlAdapter 

可能是确定数据库是否为MySQL的最佳方法.

is probably the best method of determining if your database MySQL.

尽管依赖在ActiveRecord版本之间可能会发生变化的内部信息，但我更喜欢这样做:

Despite relying on internal information that could change between ActiveRecord release, I prefer doing it this way:

ActiveRecord::Base.connection.instance_values["config"][:adapter] == "mysql"

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