Support infinity in PostgreSQL date columns

[mrnugget]

This adds support for the special input string values infinity and -infinity stored in PostgreSQL date columns.

When reading from the database the PostgreSQL adapter now returns Float::INFINITY when the stored value equals infinity and -Float::INFINITY when it equals -infinity.

Until now Rails only had support for Infinity in float and datetime columns. We need this since we have start and end dates in our project. The end date can be infinity.

Please let me know if this change is okay or if I should add something. I tried to use the same code as in OID::DateTime.

[phoet]

@mrnugget looks like one of the travis builds timed out, can you push another SHA to rebuild?

[mrnugget]

@phoet Pushed the commit again with a new SHA to my fork. I'm not sure if this trigges a new PR build though.

[phoet]

in my understanding the case statement should work with none-strings as well, do you really need the if statement?

[mrnugget]

The check is necessary because cast_value might receive Float::INFINITY, in which cause the case statement will raise an exception. See this example:

def cast_value(value)
  case value
  when 'infinity' then Float::INFINITY
  when '-infinity' then -Float::INFINITY
  else
    super
  end
end

puts cast_value('infinity')              # => Infinity
puts cast_value(Float::INFINITY)         # raises FloatDomainError

Removing the check breaks the tests.

[senny]

this is related to #17288 and #15098

/cc @matthewd

[mrnugget]

Should I rebase the branch onto current master and solve the merge conflicts or is more work needed here?

[senny]

@mrnugget I'd rather address this with #14010 and #15098.

[mrnugget]

@senny As far as I can see, both of these issues are about the column type range and the support for infinity in it. This PR here is only about date columns. Both can support infinity. But I don't see changes being made to the date column support in these issue.

Am I missing something?

[senny]

@mrnugget my bad. Please ignore this comment

[sgrif]

Is there no appropriate ruby object that we can return? I don't like the idea of having to check whether the value on a date column is a float, risking NoMethodErrors if I don't.

[mrnugget]

I'm open to suggestions! We use Float::INFINITY in our codebase and it works really well. Since we need to explicitly write Float::INFINITY to the database, we always check for it.

[mrnugget]

Is there anything I can do to get this merged? Is the Float::INFINITY solution not good enough? Should I rebase the branch again?

Edit:

It seems like I need to update the code anyway, since the OID structure of the Postgres adapter changed. Is this something worth doing? That means: is there a chance of this getting merged if I update the code?

I just rebased onto master and fixed the issues that came with the changed OID structure in the PostgresSQL adapter.

[joevandyk]

Can Float::INFINITY be compared with dates and times?

irb(main):007:0> Float::INFINITY < Time.now
ArgumentError: comparison of Float with Time failed
    from (irb):7:in `<'
    from (irb):7
    from /usr/local/bin/irb:11:in `<main>'

It would be weird to be pulling stuff from a date column that can't be compared to other dates.

[joevandyk]

See #3457 and #7350 for my previous attempts at fixing this a few years ago.

[mrnugget]

No, it's not comparable with dates and time. We handle it as a special case in our application. In the same way we use "infinity" in datetime columns, which are already supported like this.

There is Date::Infinity in the standard library though:

irb(main):020:0> Date.today < Date::Infinity.new
=> true
irb(main):025:0> Time.now < Date::Infinity.new
=> true

[sgrif]

It looks like Date::Infinity is internal to Ruby, not intended for public use. I personally don't think there's a good way to handle this. Float::INFINITY is the only reasonable value that we can use in Ruby to represent this, but I feel that returning that is too unexpected for us to perform that behavior in Rails by default.

In Rails 5, we're introducing a public API which would allow you to add support for infinite dates specifically to your application if you need this behavior and want to use Float::INFINITY to do so. Because it is possible to handle on a per-application basis, and I don't think there's a good enough generic solution for us to include in Rails proper, I think the best answer is for Rails to simply not support infinite dates out of the box.

[mrnugget]

Alright, thanks a lot for the feedback! And let me just add, that I was proposing this solution, since the support for infinity in datetime columns is already in Rails.

[sgrif]

Yeah, we're reviewing a lot of those behaviors, and that might end up getting deprecated. That's also why I want to be conservative with solutions that don't feel quite right, as they're very hard to change later.

[aried3r]

@sgrif Sorry for grave digging, but I could not find such an API in Rails 5, could you point me to it, if implemented?

[bolshakov]

@aried3r I think Sean was talking about this Attributes API https://github.com/rails/rails/blob/v4.2.1/activerecord/lib/active_record/type/value.rb
You con see a lot of examples in the same folder. To implement your oun attribute type, inherit form Type::Value and override couple of methods.

For example here I've implemented an array which is always sorted and contains only uniq elements

class OrderedArrayWithUniqElements < ActiveRecord::ConnectionAdapters::PostgreSQL::OID::Array
  def type_cast_from_user(value)
    super(value).sort.uniq
  end
end

And usage:

class PriceList < ActiveRecord::Base
    attribute :tags, OrderedArrayWithUniqElements.new(ActiveRecord::Type::String.new)
end

[justinoue]

Out of the box rails still does not seem to support postgres's 'infinity' value. I can't figure out from all the different issues what the expected behavior is, but if you google, this PR is what shows up. Trying to insert 'infinity' gets treated as nil/null. Trying to retrieve 'infinity' gets treated as nil.

To fix this I have created a custom type as follows:

# config/initializers/types.rb
class InfiniteDateType < ActiveRecord::Type::Date
  def cast(value)
    if value.kind_of?(String) && value == 'infinity'
      value
    elsif value.kind_of?(DateTime::Infinity)
      'infinity'
    else
      super
    end
  end

  def deserialize(value)
    if value.kind_of?(String) && value == 'infinity'
      DateTime::Infinity.new
    else
      super
    end
  end
end
ActiveRecord::Type.register(:infinite_date, InfiniteDateType)

and putting the following in my model

attribute :my_date, :infinite_date