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What is the fastest way to create mass HABTM associations in Rails?

Asked 2010-02-04T21:37:57.580
17

I have two tables, with a HABTM relationship in Rails. Something like the following:

class Foo < ActiveRecord::Base
  has_and_belongs_to_many :bars
end

class Bar < ActiveRecord::Base
  has_and_belongs_to_many :foos
end

Now I have a new Foo object, and want to mass-assign thousands of bars to it, which I've pre-loaded:

@foo = Foo.create
@bars = Bar.find_all_by_some_attribute(:a)

What's the fastest way to do this? I've tried:

@foo.bars = @bars
@foo.bars << @bars

And both run really slow, with an entry like the following for each bar:

bars_foos Columns (1.1ms) SHOW FIELDS FROM bars_foos SQL (0.6ms) INSERT INTO bars_foos (bar_id, foo_id) VALUES (100, 117200)

I looked at ar-extensions, but the import function doesn't seem to work without a model (Model.import) which precludes its use for a join table.

Do I need to write the SQL, or does Rails have a prettier way?

ruby-on-rails activerecord has-and-belongs-to-many
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2 Answers

7

You still might have a look at activerecord-import. It's right that it doesn't work without a model, but you could create a Model just for the import.

class FooBar < ActiveRecord::Base; end

FooBar.import [:foo_id, :bar_id], [[1,2], [1,3]]

You can wrap this in a transaction to ensure the HABTM gets fully populated, as in here:

ActiveRecord::Base.transaction do
  imported_foo = Foo.import( foo_names, foo_values )
  imported_bar = Bar.import( bar_names, bar_values )
  FooBar.import( [:foo_id, :bar_id], imported_foo.ids.zip(imported_bar.ids)
end
answered 2011-07-13T14:18:50.047
-5

Honestly, has_and_belongs_to_many is a very antiquated way of doing things. You should probably look into has_many :through, which is the new way of doing join tables, and has been for quite some time.

class Foo < ActiveRecord::Base
  has_many :foobars
  has_many :bars, :through => :foobars

  def add_many_bars(bars)
    bars.each do |bar|
      self.bars << bar
    end
  end
end

class Bar < ActiveRecord::Base
  has_many :foobars
  has_many :foos, :through => :foobars
end

class FooBar < ActiveRecord::Base
  belongs_to :foo
  belongs_to :bar
end

Also, you should try running the same in production and see what kind of performance you get, as a lot of caching goes on in production that doesn't necessarily occur in development.

answered 2010-02-06T19:24:51.977

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