Filterameter provides declarative filters for Rails controllers to reduce boilerplate code and increase readability. How many times have you seen (or written) this controller action?

def index
  @films = Films.all
  @films = @films.where(name: params[:name]) if params[:name]
  @films = @films.joins(:film_locations).merge(FilmLocations.where(location_id: params[:location_id])) if params[:location_id]
  @films = @films.directed_by(params[:director_id]) if params[:director_id]
  @films = @films.written_by(params[:writer_id]) if params[:writer_id]
  @films = @films.acted_by(params[:actor_id]) if params[:actor_id]
end

It's redundant code and a bit of a pain to write and maintain. Not to mention what RuboCop is going to say about it. Wouldn't it be nice if you could just declare the filters that the controller accepts?

  filter :name, partial: true
  filter :location_id, association: :film_locations
  filter :director_id, name: :directed_by
  filter :writer_id, name: :written_by
  filter :actor_id, name: :acted_by

  def index
    @films = build_query_from_filters
  end

Simplify and speed development of Rails controllers by making filter parameters declarative with Filterameter.

• Getting Started
• Usage
  • Filtering Options
    • Name
    • Association
    • Validates
    • Partial
    • Range
    • Sortable
  • Scope Filters
  • Sorting
  • Building the Query
  • Specifying the Model
• Configuration
• Testing Declarations
• Forms and Query Parameters
• Contribute
• License

This gem requires Rails 6.1+, and works with ActiveRecord.

Add this line to your application's Gemfile:

gem 'filterameter'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install filterameter

Include module Filterameter::DeclarativeFilters in the controller to provide the filter DSL. It can be included in the ApplicationController to make the functionality available to all controllers or it can be mixed in on a case-by-case basis.

  filter :color
  filter :size, validates: { inclusion: { in: %w[Small Medium Large], allow_multiple_values: true } }
  filter :brand_name, association: :brand, name: :name
  filter :on_sale, association: :price, validates: [{ numericality: { greater_than: 0 } },
                                                    { numericality: { less_than: 100 } }]

Filters without options can be declared all at once with filters:

filters :color,
        :size,
        :name

The following options can be specified for each filter.

If the name of the parameter is different than the name of the attribute or scope, then use the name parameter to specify the name of the attribute or scope. For example, if the attribute name is current_status but the filter is exposed simply as status use the following:

filter :status, name: :current_status

This option can also be helpful with nested filters so that the query parameter can be prefixed with the model name. See the association option for an example.

If the attribute or scope is nested, it can be referenced by naming the association. For example, if the manager_id attribute lives on an employee's department record, use the following:

filter :manager_id, association: :department

The attribute or scope can be nested more than one level. Declare the filter with an array specifying the associations in order. For example, if an employee belongs to a department and a department belongs to a business unit, use the following to query on the business unit name:

filter :business_unit_name, name: :name, association: [:department, :business_unit]

If an association is a has_many the distinct method is called on the query.

Limitation: If there is more than one association to the same table and both associations can be part of the query, then you cannot use a nested filter directly. Instead, build a scope that disambiguates the associations then build a filter against that scope.

If the filter value should be validated, use the validates option along with ActiveModel validations. Here's an example of the inclusion validator being used to restrict sizes:

filter :size, validates: { inclusion: { in: %w[Small Medium Large] } }

The inclusion validator has been overridden to provide the additional option allow_multiple_values. When true, the value can be an array and each entry in the array will be validated. Use this when the filter can specify one or more values.

filter :size, validates: { inclusion: { in: %w[Small Medium Large], allow_multiple_values: true } }

Specify the partial option if the filter should do a partial search (SQL's LIKE). The partial option accepts a hash to specify the search behavior. Here are the available options:

• match: anywhere (default), from_start, dynamic
• case_sensitive: true, false (default)

There are two shortcuts: : the partial option can be declared with true, which just uses the defaults; or the partial option can be declared with the match option directly, such as partial: :from_start.

filter :description, partial: true
filter :department_name, partial: :from_start
filter :reason, partial: { match: :dynamic, case_sensitive: true } 

The match options defines where you are searching (which then controls where the wildcard(s) appear):

• anywhere: adds wildcards at the start and end, for example '%blue%'
• from_start: adds a wildcard at the end, for example 'blue%'
• dynamic: adds no wildcards; this enables the client to fully control the search string

Specify the range option to enable searches by ranges, minimum values, or maximum values. (All of these are inclusive. A search for a minimum value of $10.00 would include all items priced at $10.00.)

Here are the available options:

• true: enable ranges, minimum values, and/or maximum values
• min_only: enables minimum values
• max_only: enables maximum values

Using the range option means that in addition to the attribute filter minimum and maximum query parameters may also be specified. The parameter names are the attribute name plus the suffix _min or _max.

filter :price, range: true
filter :approved_at, range: :min_only
filter :sale_price, range: :max_only

In the first example, query parameters could include price, price_min, and price_max.

By default most filters are sortable. To prevent an attribute filter from being sortable, set the option to false.

filter :price, sortable: false

The following filters are not sortable:

• scope filters (see Sorting with a Scope)
• filters with collection associations

For scopes that do not take arguments, the filter should provide a boolean that indicates whether or not the scope should be invoked. For example, imagine a scope called high_priority with criteria that identifies high priority records. The scope would be invoked by the query parameters high_priority=true.

Passing high_priority=false will not invoke the scope. This makes it easy to include a filter with a check box UI.

Scopes that do take arguments must be written as class methods, not inline scopes. For example, imagine a scope called recent that takes an as of date as an argument. Here is what that might look like:

def self.recent(as_of_date)
  where('created_at > ?', as_of_date)
end

As noted above, most attribute filters are sortable by default. If no filter has been declared for an attribute, the sort declaration can be used. Use the same name and association options as needed.

For example, the following declaration could be used on an activity controller to allow activities to be sorted by project created at.

sort :project_created_at, name: :created_at, association: :project

Sorts without options can be declared all at once with sorts:

sorts :created_at,
      :updated_at,
      :description

Scopes can be used for sorting, but must be declared with sort (or sorts). For example, if a model included a scope called by_created_at you could add the following to the controller to expose it.

sort :by_created_at

The name and association options can also be used. For example, if the scope was on the Project model it could also be used on a child Activity controller using the association option:

sort :by_created_at, association: :project

Only singular associations are valid for sorting. A collection association could return multiple values, making the sort indeterminate.

A scope that is used for sorting must accept a single argument. It will be passed either :asc or :desc depending on the parameter.

The example scope above might be defined as follows:

def self.by_created_at(dir)
  order(created_at: dir)
end

A default sort can be declared using default_sort. The argument(s) should specify one or more of the declared sorts or sortable filters by name. By default, the order is ascending. If you want descending order, you can map the column name symbol to :desc.

default_sort updated_at: :desc, :description

In order to provide consistent results, a sort is always applied. If no default is specified, it will use primary key descending.

There are two ways to apply the filters and build the query, depending on how much control and/or visibility is desired:

• Use the build_filtered_query before action callback
• Manually call build_query_from_filters

Add before action callback build_filtered_query for controller actions that should build the query. This can be done either in the ApplicationController or on a case-by-case basis.

When using the callback, the variable name is the pluralized model name. For example, the Photo model will use the variable @photos to store the query. The variable name can be explicitly specified with with filter_query_var_name. For example, if the query is stored as @data, use the following:

filter_query_var_name :data

Additionally, the filter_model command takes an optional second parameter to specify the variable name. Both the model and the variable name can be specified with this short-cut. For example, to use the Picture model and store the results as @data, use the following:

filter_model 'Picture', :data

In the happy path, the WidgetsController serves Widgets and can filter on size and color. Here's what the controller might look like:

class WidgetsController < ApplicationController
  include Filterameter::DeclarativeFilters
  before_action :build_filtered_query, only: :index

  filter :size
  filter :color

  def index
    render json: @widgets
  end
end

To generate the query manually, you can call build_query_from_filters directly instead of using the callback.

Here's the Widgets controller again, this time building the query manually:

class WidgetsController < ApplicationController
  include Filterameter::DeclarativeFilters

  filter :size
  filter :color

  def index
    @widgets = build_query_from_filters
  end
end

This method optionally takes a starting query. If there was a controller for Active Widgets that should only return active widgets, the following could be passed into the method as the starting point:

  def index
    @widgets = build_query_from_filters(Widget.where(active: true))
  end

The starting query is also a good place to provide any includes to enable eager loading:

  def index
    @widgets = build_query_from_filters(Widgets.includes(:manufacturer))
  end

Note that the starting query provides the model, so the model is not looked up and the model_name declaration in not needed.

Rails conventions are used to determine the controller's model. For example, the PhotosController builds a query against the Photo model. If a controller is namespaced, the model will first be looked up without the namespace, then with the namespace.

If the conventions do not provide the correct model, the model can be named explicitly with the following:

filter_model 'Picture'

Important: If the filter_model declaration is used, it must be before any filter or sort declarations.

There are three configuration options:

• action_on_undeclared_parameters
• action_on_validation_failure
• filter_key

The configuration options can be set in an initializer, an environment file, or in application.rb.

The options can be set directly...

Filterameter.configuration.action_on_undeclared_parameters = :log

...or the configuration can be yielded:

Filterameter.configure do |config|
  config.action_on_undeclared_parameters = :log
  config.action_on_validation_failuer = :log
  config.filter_key = :f
end

Occurs when the filter parameter contains any keys that are not defined. Valid actions are :log, :raise, and false (do not take action). By default, development will log, test will raise, and production will do nothing.

Occurs when a filter parameter fails a validation. Valid actions are :log, :raise, and false (do not take action). By default, development will log, test will raise, and production will do nothing.

By default, the filter parameters are nested under the key :filter. Use this setting to override the key.

If the filter parameters are NOT nested, set this to false. Doing so will restrict the filter parameters to only those that have been declared, meaning undeclared parameters are ignored (and the action_on_undeclared_parameters configuration option does not come into play).

The declarations can be tested for each controller, catching typos, incorrectly defined scopes, or any other issues. Method declarations_validator is added to each controller, and a single controller test can be added to validate all the declarations for that controller.

An RSpec test might look like this:

expect(WidgetsController.declarations_validator).to be_valid

In Minitest it might look like this:

validator = WidgetsController.declarations_validator
assert_predicate validator, :valid?, -> { validator.errors }

The filter parameters are pulled from the controller parameters, nested under the key filter (by default; see Configuration to change the filter key). For example a request for large, blue widgets might have the following query parameters on the url:

?filter[size]=large&filter[color]=blue

On a generic search form, the form_with form helper takes the option scope that allows parameters to be grouped:

<%= form_with url: "/search", scope: :filter, method: :get do |form| %>
  <%= form.label :size, "Size:" %>
  <%= form.text_field :size %>
  <%= form.label :color, "Color:" %>
  <%= form.text_field :color %>
  <%= form.submit "Search" %>
<% end %>

The sort is also nested underneath the filter key:

/widgets?filter[sort]=size

Use an array to pass multiple sorts. The order of the parameters is the order the sorts will be applied. For example, the following sorts first by size then by color:

/widgets?filter[sort]=size&filter[sort]=color

Sorts are ascending by default, but can use a prefix can be added to control the sort:

• + ascending (the default)
• - descending

For example, the following sorts by size descending:

/widgets?filter[sort]=-size

Feedback, feature requests, and proposed changes are welcomed. Please use the issue tracker for feedback and feature requests. To propose a change directly, please fork the repo and open a pull request. Keep an eye on the actions to make sure the tests and Rubocop are passing. Code Climate is also used manually to assess the codeline.

To report a bug, please use the issue tracker and provide the following information:

• the version in use
• the filter declarations
• the SQL generated (for invalid / incorrect queries)

Gold stars will be awarded if you are able to replicate the issue with a test.

Tests are written in RSpec and the dummy app uses a docker database. The script bin/start_db.sh starts and prepares the test database. It is a one-time step before running the tests.

bin/start_db.rb
bundle exec rspec

The tests can also be run across all the ruby and Rails combinations using appraisal. The install is also a one-time step.

bundle exec appraisal install
bundle exec appraisal rspec

The gem is available as open source under the terms of the MIT License.