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Might utilizes the power of Ransack gem to provide models gathering api for Rails' controllers.


Add this line to your application's Gemfile:

gem 'might'

And then execute:

$ bundle

Or install it yourself as:

$ gem install might


Define a mighty fetcher

class ChannelFetcher < Might::Fetcher
  # Specify resource to be fetched
  self.resource_class = Channel

  # Specify list of allowed filters
  filter :genres_name

  # Allowed sortings
  sort :name
  sort :created_at

And fetch resources by user input:

params = {
  'filter' => {
    'genres_name_in' => 'Horror,Drama',
  'sort' => '-created_at,name',
  'page' => {
    'limit' => 50,
    'offset' => 0
} do |result|
  if result.success?
    render json: result.get
    render json: result.errors, status: :bad_request

# or #=> ChannelFetcher::Result

params hash should follow the following conventions:

  • :filter key is used for filtering
  • :sort key is used for sorting
  • :page key is used for pagination

The result of evaluating #run method is Might::Result. It may be either success or failure. This container have the following api:

  • #success? - true if result is Success, false otherwise
  • #failure? - true if result is Failure, false otherwise
  • #get - returns fetching result if result is Success, raises exception if it is Failure
  • #errors - returns parameters processing errors (as array of strings) if result is Failure, raises exception if it is Success

NOTE: #errors returns only errors in user input, and not includes exceptions thrown during fetching process.

Configuring filters

To filter resources using Mighty Fetcher you should provide white list of allowed filters. Internally it uses Ransack gem, so consult with its documentation in case of frustration.

Simplest filter definition looks as follows:

filter :name

It allows client to filter collection on its name. So if a client want to filter on exec name it should pass a hash containing name followed by _eq predicate:
  'filter' => {
    'name_eq' => 'MTV'

If you need to pass list of values, specify them as comma separated list:
  'filter' => {
    'name_in' => 'MTV,A-One'

You may provide alias for an attributes using :as option

filter :name, as: :title

The Channel#name attribute would be exposed as title to the fetcher api.
  'filter' => {
    'title_eq' => 'MTV'

Using power of Ransack we can filter of relations' attributes. For instance to search for channels on languages with specified iso2 code, you have two options.

filter :language_iso2

Query on this attribute as is and Ransack will handle all details:
  'filter' => {
    'language_iso2_eq' => 'ru'

The second option is:

filter :iso2, on: :language
  'filter' => {
    'iso2_eq => 'ru'

It's possible to coerce attribute before using it:

filter :resource_type, coerce: ->(value) { String(value).classify }

You can whitelist predicates for each filter:

filter id: [:in, :eq]
filter name: :eq

Filtering on polymorphic association needs more configuration.

class House < ActiveRecord::Base
  has_one :location, as: :locatable

class Location < ActiveRecord::Base
  belongs_to :locatable, polymorphic: true

class LocationFetcher < Might::Fetcher
  filter :locatable_id, on: { resource: ['House'] }

User provided filters may be validated using ActiveModel::Validation

filter registration_number: :eq, validates: { length: { is: 6 } }

If value of the registration_number is invalid it raises Might::FilterValidationFailed.

List of all supported predicates

Predicate Opposite Predicate Meaning
eq not_eq field is exactly equal to a given value
matches does_not_match field is like a given value
lt gt field is less than a given value
lteq gteq field is less than or equal to a given value
in not_in field is within a specified list
cont not_cont field contains a given value
cont_any not_cont_any field contains any of given values
start not_start field begins with a given value
end not_end field ends with a given value
true not_true field is true
false not_false field is false
present blank field is present (not null and not a blank string)
null not_null field is null

Configuring sorting

Mighty Fetcher supports sorting resource collections according to one or more criteria.

sort :name
sort :created_at

To sort on one of the allowed fields provide sort parameter:'sort' => 'name')

If you need to sort against multiple fields separate them with comma. Sort fields would be applied in the order specified.'sort' => 'name,created_at')

The sort order for each sort field is ascending unless it is prefixed with a minus, in which case it is descending.'sort' => '-created_at,name')

The above example should return the newest channels first. Any articles created on the same date will then be sorted by their name in ascending alphabetical order.

Configuring components

Mighty Fetcher implements it's components as chain of middlewares (Using ibsciss-middleware)

You can disable sorting, pagination and filtering altering middleware chain.

class ChannelFetch < Fetch
  middleware.delete Might::FilterMiddleware
  middleware.insert_before Might::SortMiddleware, CustomFilterMiddleware
  middleware.use AnotherMiddleware

If you need do perform some actions before or after middleware chain:

class FavoritesFetcher < Might::Fetcher
  before do |favorites, params|
    [favorites.by_user(params[:user]), params]

To get translated error messages load Rails Railtie

require 'might/railtie'


After checking out the repo, run bin/setup to install dependencies. Then, run rake 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


Copyright 2015 SPB TV AG

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.