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Extraction of the ActiveRecord::Base#import functionality from ar-extensions for Rails 3 and beyon
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README.markdown

activerecord-import

activerecord-import is a library for bulk inserting data using ActiveRecord.

One of its major features is following activerecord associations and generating the minimal number of SQL insert statements required, avoiding the N+1 insert problem. An example probably explains it best. Say you had a schema like this:

Publishers have Books Books have Reviews

and you wanted to bulk insert 100 new publishers with 10K books and 3 reviews per book. This library will follow the associations down and generate only 3 SQL insert statements - one for the publishers, one for the books, and one for the reviews.

In contrast, the standard ActiveRecord save would generate 100 insert statements for the publishers, then it would visit each publisher and save all the books: 100 * 10,000 = 1,000,000 SQL insert statements and then the reviews: 100 * 10,000 * 3 = 3M SQL insert statements,

That would be about 4M SQL insert statements vs 3, which results in vastly improved performance. In our case, it converted an 18 hour batch process to <2 hrs.

Rails 4.0

Use activerecord-import 0.4.0 or higher.

Rails 3.1.x up to, but not including 4.0

Use the latest in the activerecord-import 0.3.x series.

Rails 3.0.x up to, but not including 3.1

Use activerecord-import 0.2.11. As of activerecord-import 0.3.0 we are relying on functionality that was introduced in Rails 3.1. Since Rails 3.0.x is no longer a supported version of Rails we have decided to drop support as well.

For More Information

For more information on activerecord-import please see its wiki: https://github.com/zdennis/activerecord-import/wiki

Additional Adapters

Additional adapters can be provided by gems external to activerecord-import by providing an adapter that matches the naming convention setup by activerecord-import (and subsequently activerecord) for dynamically loading adapters. This involves also providing a folder on the load path that follows the activerecord-import naming convention to allow activerecord-import to dynamically load the file.

When ActiveRecord::Import.require_adapter("fake_name") is called the require will be:

  require 'activerecord-import/active_record/adapters/fake_name_adapter'

This allows an external gem to dyanmically add an adapter without the need to add any file/code to the core activerecord-import gem.

Load Path Setup

To understand how rubygems loads code you can reference the following:

http://guides.rubygems.org/patterns/#loading_code

And an example of how active_record dynamically load adapters: https://github.com/rails/rails/blob/master/activerecord/lib/active_record/connection_adapters/connection_specification.rb

In summary, when a gem is loaded rubygems adds the lib folder of the gem to the global load path $LOAD_PATH so that all require lookups will not propegate through all of the folders on the load path. When a require is issued each folder on the $LOAD_PATH is checked for the file and/or folder referenced. This allows a gem (like activerecord-import) to define push the activerecord-import folder (or namespace) on the $LOAD_PATH and any adapters provided by activerecord-import will be found by rubygems when the require is issued.

If fake_name adapter is needed by a gem (potentially called activerecord-import-fake_name) then the folder structure should look as follows:

activerecord-import-fake_name/
|-- activerecord-import-fake_name.gemspec
|-- lib
|   |-- activerecord-import-fake_name
|   |   |-- version.rb
|   |-- activerecord-import
|   |   |-- active_record
|   |   |   |-- adapters
|   |   |       |-- fake_name_adapter.rb
|--activerecord-import-fake_name.rb

When rubygems pushes the lib folder onto the load path a require will now find activerecord-import/active_record/adapters/fake_name_adapter as it runs through the lookup process for a ruby file under that path in $LOAD_PATH

License

This is licensed under the ruby license.

Author

Zach Dennis (zach.dennis@gmail.com)

Contributors

  • Blythe Dunham
  • Gabe da Silveira
  • Henry Work
  • James Herdman
  • Marcus Crafter
  • Thibaud Guillaume-Gentil
  • Mark Van Holstyn
  • Victor Costan
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