【Rails】使用serialize

ActiveRecord::Base serialize

Rails 中通过使用 serialize 直接将对象转化为字符串保存在数据库中。

class User < ActiveRecord::Base
  serialize :group_ids
end

通过以上的方式，User#group_ids 被字符串化并保存，并不需要其他多余的处理。

> User.create(name: 'Aclice', group_ids: [1, 2, 3])
> User.save

在数据库中，数据以字符串的形式保存：

> select * from users;
1|alice|---\n- 1\n- 3\n- 5|2013-12-11 14:18:07.344781|2013-12-11 14:18:07.344781

以正常方式取出数据：

> user = User.find(1)
  User Load (0.3ms)  SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
=> #<User id: 1, name: "alice", group_ids: [1, 3, 5], created_at: "2013-12-11 14:18:07", updated_at: "2013-12-11 14:18:07">
> user.group_ids
=> [1, 3, 5]
> user.group_ids.class
=> Array

需要注意的是，serialize 的使用会消耗大量的时间，因此在大部分系统中遭到弃用。

对象类型

可以通过 serialize 所带的第二个参数来指定队形的类型，如 Hash, Array, Json

class User < ActiveRecord::Base
  serialize :group_ids, Array
end

> User.create(name: 'bob', group_ids: '1,2,3')
   (0.1ms)  begin transaction
   (0.1ms)  rollback transactionActiveRecord::SerializationTypeMismatch: Attribute was supposed to be a Array, but was a String. -- "1,2,3

如果与对象的类型不符，则会显示 ‘ActiveRecord::SerializationTypeMismatch’ 错误。

测试用例

describe '.serialize' do
  let(:user) { build :user }

  context 'when group_ids given the Array object' do
    subject { user.group_ids }
    before do
      user.group_ids = [1, 3, 5]
      user.save
    end
    it { should match_array [1,3,5] }
  end

  context 'when group_ids given an invalid object' do
    [12345, 'string value', {key: 'value'}].each do |invalid_object|
      before { user.group_ids = invalid_object }
      it { expect { user.save }.to raise_error(ActiveRecord::SerializationTypeMismatch) }
    end
  end
end