Ruby / Rails-如何验证小数位数？ [英] Ruby/Rails - How can you validate against decimal scale?

问题描述

如何验证小数位数？例如，假设我们要存储小数点后最多2个小数点的酒店的评分。 4.34。 3.76。等等

我在网上阅读了根据您与列相关的精度/比例截断的sqlite。因此，如果您的精度为3，小数位数为2，然后输入1.34567，则将存储1.35。我输入了这个值，尽管我的精度为3，但DB仍以某种方式存储了全部内容。

  t.decimal：my_column，precision ：3，比例尺：2 
  

所以，如何验证这种情况，为什么呢？ postgres会存储大于2的小数位数吗？

解决方案

小数位数仅在值是字符串时才重要。将其转换为数字后，它具有的小数位数很多，为零或更多。

因此，进行此验证的时间取决于输入（当这是一个字符串，因为用户输入的 all 总是 一个字符串），然后再次在输出上强制正确显示为字符串。在其他所有时间，您都不必担心小数位数。

就Rails而言，您可以使用访问器方法来为您做一些验证：

  def my_column =（value）
 if value [/\A\d+\.\d\ d\z /] 
 write_attribute：my_column，值
 else 
 errors.add（：my_column，：invalid）
结束
结束
  

您不能使用传统的验证器，因为字符串->十进制转换将在验证器运行之前发生。

How you can validate against the scale of a decimal? For example, let's say we want to store ratings for a hotel with maximum 2 decimal points after the decimal. 4.34. 3.76. etc

I've read online that sqlite with truncate based on the precision/scale you've tied to the column. So if you have a precision 3, scale 2, and enter 1.34567 1.35 will be stored.

However, I'm using postgres and this is not the case. I enter this, and the DB stores the full thing somehow despite my precision 3 scale 2.

t.decimal :my_column, precision: 3, scale: 2

So, how do I validate against this kind of thing, and why is postgres storing more than 2 decimal scale to begin with?

解决方案

The number of decimal places only matters when the value is a string. Once you've converted it to a number, it has however many decimals it has, zero or more.

So, the time to do this validation is on input (when it's a string, as all input from the user is always a string) and then enforce the correct display on output, when it is again a string. At all other times, you should not worry about the number of decimals.

In terms of Rails, you can use an accessor method which does some validation for you:

def my_column=(value)
  if value[/\A\d+\.\d\d\z/]
    write_attribute :my_column, value
  else
    errors.add(:my_column, :invalid) 
  end
end

You can't use a traditional validator as the string->decimal conversion will happen before your validator runs.

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