Question

我刚注意到一些让我有点麻烦的事情。

我正在创建一个对象。该对象使用以下内容进入数据库：

created_at: "2015-11-12 08:37:35.413663"

我没有意识到它存储超出.413

您可以通过执行以下操作确认已保存，而不仅仅是为了我们的观看乐趣：object.created_at.nsec #=> 413663000

当我的前端收到我的JSON时，created_at属性变为："2015-11-12T08:37:35.413Z"，这是我期望的。这里的问题是我们丢失了有价值的信息，因为现在我们没有633微秒。

的确，如果你做"2015-11-12T08:37:35.413Z".to_time.nsec #=> 413000000。

这意味着当您执行以下操作时，您将不会获得任何项目：

Object.where(created_at: object.created_at.as_json).first #=> nil

如何缓解这种情况？如何计算微秒，或者更确切地说，查询created_at，只需毫秒精度。

Answer 1

Ultimately, I decided on changing the datetime columns in my DB.

I basically applied the following wherever relevant in a migration:

change_column table, column, :datetime, limit: 3

That successfully makes sure that my :datetime columns all only go to the milliseconds.

I think it is a good change because when the sole purpose of my back-end is to render a JSON API, then I think through and through it should be cohesive. JSON API standards are ISO 8601. As such, I'd like my DB to adhere to that.

Answer 2

DateTime.now.to_s不会返回小数秒，因为您需要更高的精度，您可以在创建的参数中使用DateTime.now.iso8601(10)。

m = ModelName.create(created_at: DateTime.now.iso8601(10))

或

m = ModelName.create()
m.created_at = DateTime.now.iso8601(10)
m.save

我尝试过有点类似于你所描述的测试：

p=Product.create(created_at: DateTime.now.iso8601(10))
p.created_at.nsec
=> 61103188

 Product.where(created_at: p.created_at)
=> #<ActiveRecord::Relation [#<Product id: 172, manufacturer: nil, created_at: "2015-11-12 10:11:31", updated_at: "2015-11-12 10:11:31", avatar: nil>]>

创建对象时，created_at存储json无法匹配的微秒精度

2 个答案: