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https://github.com/userlist/active_model-relation

Query collections of ActiveModel objects like an ActiveRecord::Relation
https://github.com/userlist/active_model-relation

active-model rails ruby

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Query collections of ActiveModel objects like an ActiveRecord::Relation

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README 

        
# ActiveModel::Relation



Query a collection of ActiveModel objects like an ActiveRecord::Relation.



## Installation



Install the gem and add to the application's Gemfile by executing:



    $ bundle add active_model-relation



If bundler is not being used to manage dependencies, install the gem by executing:



    $ gem install active_model-relation



## Usage



### Initialization



Create a new relation by passing the model class and a collection:



```ruby

relation = ActiveModel::Relation.new(Project, [

  Project.new(id: 1, state: 'draft', priority: 1),

  Project.new(id: 2, state: 'running', priority: 2),

  Project.new(id: 3, state: 'completed', priority: 3),

  Project.new(id: 4, state: 'completed', priority: 1)

])

```



As an alternative, it's also possible to create a collection for a model without explicitly passing a collection.

In this case, the library will attempt to call `Project.records` to get the default collection. If the method doesn't exist or returns `nil`, the collection will default to an empty array.



```ruby

class Project

  def self.records

    [

      Project.new(id: 1, state: 'draft', priority: 1),

      Project.new(id: 2, state: 'running', priority: 2),

      Project.new(id: 3, state: 'completed', priority: 3),

      Project.new(id: 4, state: 'completed', priority: 1)

    ]

  end

end



relation = ActiveModel::Relation.new(Project)

```



### Querying



An `ActiveModel::Relation` can be queried almost exactly like an `ActiveRecord::Relation`.



#### `#find`



You can look up a record by it's primary key, using the `find` method. If no record is found, it will raise a `ActiveModel::RecordNotFound` error.



```ruby

project = relation.find(1)

```



By default, `ActiveModel::Relation` will assume `:id` as the primary key. You can customize this behavior by setting a `primary_key` on the model class.



```ruby

class Project

  def self.primary_key = :identifier

end

```



When passed a block, the `find` method will behave like `Enumerable#find`.



```ruby

project = relation.find { |p| p.id == 1 }

```



#### `#find_by`



To look up a record based on a set of arbitary attributes, you can use `find_by`. It accepts the same arguments as `#where` and will return the first matching record.



```ruby

project = relation.find_by(state: 'draft')

```



#### `#where`



To filter a relation, you can use `where` and pass a set of attributes and the expected values. This method will return a new `ActiveModel::Relation` that only returns the matching records, so it's possible to chain multiple calls. The filtering will only happen when actually accessing records.



```ruby

relation.where(state: 'completed')

```



The following two lines will return the same filtered results:



```ruby

relation.where(state: 'completed', priority: 1)

relation.where(state: 'completed').where(priority: 1)

```



To allow for more advanced filtering, `#where` allows filtering using a block. This works similar to `Enumerable#select`, but will return a new `ActiveModel::Relation` instead of an already filtered array.



```ruby

relation.where { |p| p.state == 'completed' && p.priority == 1 }

```



#### `#where.not`



Similar to `#where`, the `#where.not` chain allows you to filter a relation. It will also return a new `ActiveModel::Relation` with that returns only the matching records.



```ruby

relation.where.not(state: 'draft')

```



To allow for more advanced filtering, `#where.not` allows filtering using a block. This works similar to `Enumerable#reject`, but will return a new `ActiveModel::Relation` instead of an already filtered array.



```ruby

relation.where.not { |p| p.state == 'draft' && p.priority == 1 }

```



### Sorting



It is possible to sort an `ActiveModel::Relation` by a given set of attribute names. Sorting will be applied after filtering, but before limits and offsets.



#### `#order`



To sort by a single attribute in ascending order, you can just pass the attribute name to the `order` method.



```ruby

relation.order(:priority)

```



To specify the sort direction, you can pass a hash with the attribute name as key and either `:asc`, or `:desc` as value.



```ruby

relation.order(priorty: :desc)

```



To order by multiple attributes, you can pass them in the order of specificity you want.



```ruby

relation.order(:state, :priority)

```



For multiple attributes, it's also possible to specify the direction.



```ruby

relation.order(state: :desc, priority: :asc)

```



### Limiting and offsets



#### `#limit`



To limit the amount of records returned in the collection, you can call `limit` on the relation. It will return a new `ActiveModel::Relation` that only returns the given limit of records, allowing you to chain multiple other calls. The limit will only be applied when actually accessing the records later on.



```ruby

relation.limit(10)

```



#### `#offset`



To skip a certain number of records in the collection, you can use `offset` on the relation. It will return a new `ActiveModel::Relation` that skips the given number of records at the beginning. The offset will only be applied when actually accessing the records later on.



```ruby

relation.offset(20)

```



### Scopes



After including `ActiveModel::Relation::Model`, the library also supports calling class methods defined on the model class as part of the relation.



```ruby

class Project

  include ActiveModel::Model

  include ActiveModel::Attributes

  include ActiveModel::Relation::Model



  attribute :id, :integer

  attribute :state, :string, default: :draft

  attribute :priority, :integer, default: 1



  def self.completed

    where(state: 'completed')

  end

end

```



Given the example above, you can now create relations like you're used to from `ActiveRecord::Relation`.



```ruby

projects = Project.all

completed_projects = all_projects.completed

important_projects = all_projects.where(priority: 1)

```



### Spawning



It's possilbe to create new versions of a `ActiveModel::Relation` that only includes certain aspects of the `ActiveModel::Relation` it is based on. It's currently possible to customize the following aspects: `:where`, `:limit`, `:offset`.



#### `#except`



To create a new `ActiveModel::Relation` without certain aspects, you can use `except` and pass a list of aspects, you'd like to exclude from the newly created instance. The following example will create a new `ActiveModel::Relation` without any previously defined limit or offset.



```ruby

relation.except(:limit, :offset)

```

#### `#only`



Similar to `except`, the `only` method will return a new instance of the `ActiveModel::Relation` it is based on but with only the passed list of aspects applied to it.



```ruby

relation.only(:where)

```



### Extending relations



#### `#extending`



In order to add additional methods to a relation, you can use `extending`. You can either pass a list of modules that will be included in this particular instance, or a block defining additional methods.



```ruby

module Pagination

  def page_size = 25



  def page(page)

    limit(page_size).offset(page.to_i * page_size)

  end



  def total_count

    except(:limit, :offset).count

  end

end



relation.extending(Pagination)

```



The following example is equivalent to the example above:



```ruby

relation.extending do

  def page_size = 25



  def page(page)

    limit(page_size).offset(page.to_i * page_size)

  end



  def total_count

    except(:limit, :offset).count

  end

end

```



## 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 the created tag, 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/userlist/active_model-relation. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the [code of conduct](https://github.com/userlist/active_model-relation/blob/main/CODE_OF_CONDUCT.md).



## Acknowledgements



This library is _heavily_ inspired by [`ActiveRecord::Relation`](https://github.com/rails/rails/blob/main/activerecord/lib/active_record/relation.rb) and uses similar patterns and implementations in various parts.



## License



The gem is available as open source under the terms of the [MIT License](https://opensource.org/licenses/MIT).



## Code of Conduct



Everyone interacting in the ActiveModel::Relation project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the [code of conduct](https://github.com/userlist/active_model-relation/blob/main/CODE_OF_CONDUCT.md).



## What is Userlist?



[![Userlist](https://userlist.com/images/external/userlist-logo-github.svg)](https://userlist.com/)



[Userlist](https://userlist.com/) allows you to onboard and engage your SaaS users with targeted behavior-based campaigns using email or in-app messages.



Userlist was started in 2017 as an alternative to bulky enterprise messaging tools. We believe that running SaaS products should be more enjoyable. Learn more [about us](https://userlist.com/about-us/).