ActiveRecord Find By Year, Day or Month on a Date field

Question

I have an ActiveRecord model that has a date attribute. Is it possible to utilize that date attribute to find by Year, Day and Month:

Model.find_by_year(2012)
Model.find_by_month(12)
Model.find_by_day(1)

or is it simply possible to find_by_date(2012-12-1).

I was hoping I could avoid creating Year, Month and Day attributes.

Solution 1

Assuming that your "date attribute" is a date (rather than a full timestamp) then a simple where will give you your "find by date":

Model.where(:date_column => date)

You don't want find_by_date_column as that will give at most one result.

For the year, month, and day queries you'd want to use the extract SQL function:

Model.where('extract(year  from date_column) = ?', desired_year)
Model.where('extract(month from date_column) = ?', desired_month)
Model.where('extract(day   from date_column) = ?', desired_day_of_month)

However, if you're using SQLite, you'd have to mess around with strftime since it doesn't know what extract is:

Model.where("cast(strftime('%Y', date_column) as int) = ?", desired_year)
Model.where("cast(strftime('%m', date_column) as int) = ?", desired_month)
Model.where("cast(strftime('%d', date_column) as int) = ?", desired_day_of_month)

The %m and %d format specifiers will add leading zeroes in some case and that can confuse the equality tests, hence the cast(... as int) to force the formatted strings to numbers.

ActiveRecord won't protect you from all the differences between databases so as soon as you do anything non-trivial, you either have to build your own portability layer (ugly but sometimes necessary), tie yourself to a limited set of databases (realistic unless you're releasing something that has to run on any database), or do all your logic in Ruby (insane for any non-trivial amount of data).

The year, month, and day-of-month queries will be pretty slow on large tables. Some databases let you add indexes on function results but ActiveRecord is too stupid to understand them so it will make a big mess if you try to use them; so, if you find that these queries are too slow then you'll have to add the three extra columns that you're trying to avoid.

If you're going to be using these queries a lot then you could add scopes for them but the recommended way to add a scope with an argument is just to add a class method:

Using a class method is the preferred way to accept arguments for scopes. These methods will still be accessible on the association objects...

So you'd have class methods that look like this:

def self.by_year(year)
    where('extract(year from date_column) = ?', year)
end
# etc.

Solution 2

Database independent version ...

def self.by_year(year)
  dt = DateTime.new(year)
  boy = dt.beginning_of_year
  eoy = dt.end_of_year
  where("published_at >= ? and published_at <= ?", boy, eoy)
end

Solution 3

In your Model:

scope :by_year, lambda { |year| where('extract(year from created_at) = ?', year) }

In your Controller:

@courses = Course.by_year(params[:year])

Solution 4

For MySQL try this out

Model.where("MONTH(date_column) = 12")
Model.where("YEAR(date_column) = 2012")
Model.where("DAY(date_column) = 24")

Solution 5

Simple Implementation for Just The Year

app/models/your_model.rb

scope :created_in, ->( year ) { where( "YEAR( created_at ) = ?", year ) }

Usage

Model.created_in( 1984 )

View more solutions

Comments

[mu is too short]

A day is not an open interval, it is a half-open interval.

[mu is too short]

'd >= ? and d < ?', dt.beginning_of_day, dt.tomorrow.beginning_of_day. Using < and > misses the boundary between days.

[Mutuelinvestor]

Thanks for a great answer. It seems to do this you have to rely upon database specfic function which defeats one of the benefits of activerecord. Perhaps that's why you see dates broken out by month, day and year so often. Thanks a again.

[apneadiving]

always impressed by the quality of your answers

[ITmeze]

i am not quite sure this is something that Mutuelinvestor was asking for as it does not cover case when user is asking for all posts from April, neglecting 'year' part

[d_rail]

There's also beginning_of_day/end_of_day and beginning_of_month/end_of_month for the other implementations.

[Sixty4Bit]

This is a far superior answer since it will use an index if available. Mu's will do a table scan.

[Jay El-Kaake]

This was really helpful, although for SQLite I had to CAST the date number to an integer instead of adding 0 (adding 0 gave me the wrong number for some reason). My revised filters are then: Model.where("CAST(strftime('%Y', date_column) as INT) = ?", desired_year) Model.where("CAST(strftime('%m', date_column) as INT) = ?", desired_month) Model.where("CAST(strftime('%d', date_column) as INT) = ?", desired_day_of_month)

[mu is too short]

@JayEl-Kaake: I think an explicit cast(... as int) is better than trickery in any case, I'm not sure why I didn't use cast in the first place.

[Heriberto Magaña]

No need for extract method in pg you can use TO_CHAR with ILIKE in only one line, I posted the full example at the end of this thread

[monteirobrena]

@NarenP I don't think so. PostgreSQL haven't the MONTH function. Try extract or date_part. wiki.postgresql.org/wiki/MONTH()_equivalent postgresqltutorial.com/postgresql-date_part

[Giridharan]

but iam using sqlite3 how to do this

[mu is too short]

@giridharan There's a "However, if you're using SQLite, you'd have to mess around with strftime since it doesn't know what extract is" section already there.

[Whatcould]

dt = DateTime.new(year) is already the beginning of the year; you don't need the extra datetime. Eg, boy = DateTime.new(year); eoy = boy.end_of_year