# BulkLoader

## Example

```ruby
# app/models/post.rb

class Post < ApplicationRecord
  include BulkLoader::DSL

  bulk_loader :comment_count, :id, default: 0 do |ids|
    Comment.where(id: ids).group(:post_id).count
  end
end

```

You can use this like followings:

```ruby
# app/controllers/posts_controller.rb
class PostsController < ApplicationController
  def index
    @posts = Post.limit(10)

    # load comment_count blocks with mapping by #id
    # you can avoid N+1 queries.
    Post.bulk_loader.load(:comment_count, @posts)

    render(json: @posts.map {|post| { id: post.id, comment_count: post.comment_count } })
  end
end
```

## Description

BulkLoader::DSL only create bulk\_loader class method and bulk\_loader method.
So you can use with any object that is not ActiveRecord.

### Defining bulk\_loader method

If you include BulkLoader::DSL, you can use bulk\_loader class method.

```ruby
class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: nil do |mapped_keys|
    # something with mapped_keys
    {
      mapped_key => value, # you should return Hash that has mapped_key as key.
    }
  end
end
```

that create a instance method that name is :name.

#### mapped\_key

mapped\_key is Symbol or Proc. if you want to use original object, you can pass `->(your_model) { your_model } `.

#### default option

If block's result return Hash that cannot mapped to original object, you can return value using default option.
If you does not pass default option, default is nil.

If you want to pass object like Array, you should use with lambda.

```ruby
class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: -> { [] } do |mapped_keys|
    # something with mapped_keys
    {
      mapped_key => value, # you should return Hash that has mapped_key as key.
    }
  end
end
```

#### export: false

:name method is just shorthand for bulk\_loader.public\_send(:name). So if you not want to create :name method, you can pass export: false to bulk\_loader definition.

```ruby
class YourModel
  include BulkLoader::DSL

  bulk_loader :name, :mapped_key, default: nil, export: false do |mapped_keys|
    # something with mapped_keys
  end
end
```

then you can use this like followings.

```ruby
  YourModel.new.bulk_loader.name
```

## Installation

Add this line to your application's Gemfile:

```ruby
gem 'bulk_loader'
```

And then execute:

    $ bundle

Or install it yourself as:

    $ gem install bulk_loader

## Development

After checking out the repo, run `bin/setup` to install dependencies. Then, run `rake spec` to run the tests. You can also run `bin/console` for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run `bundle exec rake install`. To release a new version, update the version number in `version.rb`, and then run `bundle exec rake release`, which will create a git tag for the version, push git commits and tags, and push the `.gem` file to [rubygems.org](https://rubygems.org).

## Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/walf443/bulk_loader.