h1. Datetime Deltas for Thinking Sphinx

h2. Installation

You'll need Thinking Sphinx 1.3.0 or later (v3 is now supported since the 2.0.0 release of this gem).

<pre><code>gem install ts-datetime-delta</code></pre>

In your Gemfile, you can use it like so:

<pre><code>gem 'ts-datetime-delta', '~> 2.0.0',
  :require => 'thinking_sphinx/deltas/datetime_delta'</code></pre>

Or if you're still on Rails 2, then put this in your @environment.rb@ file with the rest of your gem dependencies:

<pre><code>config.gem 'ts-datetime-delta',
  :lib     => 'thinking_sphinx/deltas/datetime_delta'
  :version => '>= 2.0.0'</code></pre>

No matter which version of Rails, you'll need to add the following line to the bottom of your @Rakefile@:

<pre><code>require 'thinking_sphinx/deltas/datetime_delta/tasks'</code></pre>

h2. Usage

For the indexes you want to use this delta approach, make sure you set that up in your index definition. For Thinking Sphinx v3, that'll look like this:

<pre><code>ThinkingSphinx::Index.define(:book,
  :with  => :active_record,
  :delta => ThinkingSphinx::Deltas::DatetimeDelta
) do
  # ...
end</code></pre>

But for Thinking Sphinx v1/v2, it belongs within your @define_index@ blocks:

<pre><code>define_index do
  # ...

  set_property :delta => :datetime
end</code></pre>

If you want to use a column other than @updated_at@, you can specify it using the @:delta_column@ option. The same goes for the threshold, which defaults to one day.

Again, Thinking Sphinx v3 expects these options outside the block:

<pre><code>ThinkingSphinx::Index.define(:book,
  :with          => :active_record,
  :delta         => ThinkingSphinx::Deltas::DatetimeDelta,
  :delta_options => {:threshold => 1.hour, :delta_column => :changed_at}
) do
  # ...
end</code></pre>

But Thinking Sphinx v1/v2 it goes within the @define_index@ block:

<pre><code>set_property :delta => :datetime,
  :threshold    => 1.hour,
  :delta_column => :changed_at</code></pre>

Then, while your Rails application is running, you'll need to run the delta indexing rake task regularly - as often as your threshold, allowing for some time for the indexing to actually happen.

For example, if you're going to run the delta indexing task every hour, I would recommend setting your threshold to 70 minutes.

To ensure this rake task is called regularly, it's best to set it up as a recurring task via cron or similar tools.

<pre><code>rake thinking_sphinx:index:delta</code></pre>

The shorthand version is:

<pre><code>rake ts:in:delta</code></pre>

h2. Contributors

* "W. Andrew Loe III":http://andrewloe.com/ - Environment variable for disabling merging.
* "Kirill Maximov":http://kirblog.idetalk.com - Handling nil timestamp column values for toggled checks.
* "Timo Virkkala":https://github.com/weetu - Thinking Sphinx v3 compatibility,fix for null timestamps.
* "Cedric Maion":https://github.com/cmaion - Fix for keeping custom options persisted.

h2. Copyright

Copyright (c) 2009-2014 Pat Allan, and released under an MIT Licence.