默认的ActiveRecord的迁移连载专栏 [英] default for serialized column in activerecord migration

问题描述

所以我有一个序列化列：尺寸，并在我的移民，我想设置字段设置为默认的哈希值

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

我已经尝试过...

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

和刚

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

但字段最终空。我怎么能在创建设置默认的序列化对象这个领域，或者至少确保我的连载属性始终是一个哈希？

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

在Rails的序列化的哈希保存在数据库中，它的作用是将其转换为YAML，以便它可以保存为一个字符串。为了得到这个在迁移工作，所有你需要做的是哈希转换为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，在初始化之后的模型设置...

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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