可以使用Rails迁移来转换数据吗? [英] Can Rails Migrations be used to convert data?

问题描述

我正在尝试在Rails应用程序中转换列，出于参数考虑，让我们假装我正在尝试将users表中的age列更改为字符串表示形式，而不是整数.

I'm trying to convert a column in my Rails app, for arguments sake let's pretend I'm trying to change the age column in my users table to a string representation rather than an int.

在我的迁移中，我有这个；

In my migration I have this;

def.self up
    add_column :users, :age_text, :string

    users = User.find(:all)

    users.each do |u|
       u.age_text = convert_to_text(u.age)
       u.save
    end
end

def self.convert_to_text(number)
   #code here to convert 1 to 'one' etc
end

但是它似乎没有用，我在这里尝试甚至可以进行迁移吗?

But it doesn't seem to be working, is what I'm attempting here even possible with migrations?

推荐答案

您正在尝试做的事情是可能的，我会说正确的事情.

What you're trying to do is possible, and I would say the correct thing to do.

但是，您需要为迁移中要更新的模型类重新加载列信息，以便Rails知道新列.试试这个:

You need, though, to reload the column info for the model classes you're updating in the migration, so that Rails knows about the new columns. Try this:

def.self up
    add_column :users, :age_text, :string

    User.reset_column_information 

    users = User.find(:all)

    users.each do |u|
       u.age_text = convert_to_text(u.age)
       u.save
    end
end

另外，请注意，如果您的桌子很大，那么一一进行更新将需要很长的时间..请注意这一点.

On a separate note, please note that if your table is large, doing updates one by one will take a looong time.. Be careful with that.

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