activerecord 迁移中序列化列的默认值

问题描述

所以我有一个序列化列 :dimensions，在我的迁移中，我想将该字段设置为默认哈希.

so i have a serialized column :dimensions, and in my migration, i would like to set the field to be a default hash.

我试过了……

create_table :shipping_profiles do |t|
      t.string      :dimensions_in, :default => {:width => 0, :height => 0, :depth => 0}

只是

t.string :dimensions_in, :default => Hash.new()

但字段最终为空.如何在创建时为此字段设置默认序列化对象，或者至少确保我的序列化属性始终是哈希?

but the fields end up null. how can i set a default serialized object for this field on creation, or at least make sure my serialize attribute is always a hash?

推荐答案

当Rails 序列化一个hash 以保存在db 中时，它所做的只是将它转换为YAML 以便它可以存储为一个字符串.要让它在迁移中工作，您需要做的就是将哈希转换为 yaml...

When Rails serializes a hash to save in the db, all it does is convert it to YAML so that it can be stored as a string. To get this to work in the migration, all you need to do is convert the hash to yaml...

t.string :dimensions_in, :default => {:width => 0, :height => 0, :depth => 0}.to_yaml

或者，或者，在初始化后将其设置在模型中...

Or, alternatively, set it in the model after initialization...

class ShippingProfile < ActiveRecord::Base

  after_initialize :set_default_dimensions

  private

    def set_default_dimensions
      self.dimensions_in ||= {:width => 0, :height => 0, :depth => 0}
    end

end

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