ActiveRecord: Store Milliseconds (or Microseconds) in Timestamps/Datetimes with Rails / MySQL

add_milliseconds_to_mysql_and_activerecord_timestamps.md

ActiveRecord: Store Milliseconds (or Microseconds) in Timestamps with Rails / MySQL

Milliseconds in your Timestamps.

We got 'em, you want 'em.

Why

Shit needs to be PRECISE

LICENSE

MIT

milliseconds_migration.rb

class MillisecondsMigration < ActiveRecord::Migration
  # Include non default date stamps here
  # Key   :table_name
  # value [:column_names]
  # NOTE: only MySQL 5.6.4 and above supports DATETIME's with more precision than a second.
  TABLES_AND_COLUMNS =  {
    # Your :table_names here
  }
  
  STANDARD_ACTIVE_RECORD_COLUMNS = [:created_at, :updated_at]
  
  TABLE_AND_COLUMNS.each {|k,v| v.concat(STANDARD_ACTIVE_RECORD_COLUMNS)}
  
  def up
    TABLE_AND_COLUMNS.each do |table, columns|
      columns.each do |column|
        # MySQL supports time precision down to microseconds -- DATETIME(6)
        change_column table, column, :datetime, limit: 3
      end
    end
  end

  def down
    TABLE_AND_COLUMNS.each do |table, columns|
      columns.each do |column|
        echange_column table, column, :datetime
      end
    end
  end
end

time.rb

# Save this in config/initializers/WHATEVER.rb
class Time
  # Ruby will complain that it has already initialzed DATE_FORMATS because it has...
  DATE_FORMATS = {
    # Where 3N is the number of places after the decimal (.)
    # If you want microseconds change 3N to 6N
    :db => '%Y-%m-%d %H:%M:%S.%3N'
  }
end

No problem!

Thanks, was helpful for me!

Time::DATE_FORMATS.merge!({ db: '%Y-%m-%d %H:%M:%S.%3N' }) also works for me and avoids the warning.

For (my own) reference: MySQL 5.6.4 changelog

is "echange_column" supposed to be "change_column"

This also works great for Postgresql, BUT, I will add that time.rb ended up creating errors when I tried to create or update objects. My error being PG::InvalidDatetimeFormat. Not using time.rb and everything is perfect.

Nice. Here's if you want to convert all datetime columns, add indexes and avoid the Time warning:

class MillisecondsDateTime < ActiveRecord::Migration
  def up
    ActiveRecord::Base.connection.tables.each do |table|
      ActiveRecord::Base.connection.columns(table).each do |column|
        if column.type == :datetime
          change_column table, column.name, :datetime, limit: 6
          add_index table, column.name
        end
      end
    end
  end

  def down
    ActiveRecord::Base.connection.tables.each do |table|
      ActiveRecord::Base.connection.columns(table).each do |column|
        if column.type == :datetime
          change_column table, column.name, :datetime
          remove_index table, column.name
        end
      end
    end
  end
end

app/config/initializers/time.rb

Time::DATE_FORMATS[:db] = '%Y-%m-%d %H:%M:%S.%6N'

The initializer is not necessary with Rails 4.2.5. It just works with the correct database type DATETIME(6).
Additionally, adding this into an initializer will fix your migrations. All that is left after that is to make the change retroactive.

# Creates DATETIME(6) column types by default which support microseconds.
#
# Without it, regular DATETIME columns are created and Percona does not attach
# microseconds to the default DATETIME types. This has a rich history, refer to
# SQL Server DATETIME2.
ActiveRecord::ConnectionAdapters::AbstractMysqlAdapter::NATIVE_DATABASE_TYPES[:datetime][:limit] = 6

I've created an updated gist with feedback from this thread.

See https://gist.github.com/MarkMurphy/93adca601b05acffb8b5601df09f66df

• Fixes a typo or two
• Migrates all table columns with type :datetime
• Adds default :limit to AbstractMysqlAdapter::NATIVE_DATABASE_TYPES[:datetime] for future migrations.
• Fixes "Time::DATE_FORMATS is already initialized"
• Defaults precision to 6 instead of 3 because may as well.

Is there a way to implement this in Teensy 4.1 or Arduino ? I am trying to develop a gunshot localization program to solve local gunfire at 2AM-4AM.