ActiveRecord Find By Year, Day or Month on a Date

问题:

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.

回答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.

回答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

回答3:

For MySQL try this out

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

回答4:

In your Model:

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

In your Controller:

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

回答5:

I think the easiest way to do this is a scope:

scope :date, lambda {|date| where('date_field > ? AND date_field < ?', DateTime.parse(date).beginning_of_day, DateTime.parse(date).end_of_day}

Use it like this:

Model.date('2012-12-1').all

That will return all models with a date_field between the beginning and end of day for the date you send.

回答6:

Try this:

Model.where("MONTH(date_column) = ? and DAY(date_column) = ?", DateTime.now.month, DateTime.now.day)

回答7:

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 )

回答8:

I like BSB's answer but as a scope

scope :by_year, (lambda do |year| 
  dt = DateTime.new(year.to_i, 1, 1)
  boy = dt.beginning_of_year
  eoy = dt.end_of_year
  where("quoted_on >= ? and quoted_on <= ?", boy, eoy)
end)

回答9:

This would be another one:

def self.by_year(year)
  where("published_at >= ? and published_at <= ?", "#{year}-01-01", "#{year}-12-31")
end

Works pretty well for me in SQLite.

回答10:

No need for extract method, this works like a charm in postgresql:

text_value = "1997" # or text_value = '1997-05-19' or '1997-05' or '05', etc
sql_string = "TO_CHAR(date_of_birth::timestamp, 'YYYY-MM-DD') ILIKE '%#{text_value.strip}%'"
YourModel.where(sql_string)

回答11:

Another short scope as below:

  class Leave
    scope :by_year, -> (year) {
      where(date:
                Date.new(year).beginning_of_year..Date.new(year).end_of_year)
    }
  end

Call the scope:

Leave.by_year(2020)

回答12:

In Postgresql v 11+(i've tested): below way works

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