README.md
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# Table of Contents
- [Grape::Entity](#grapeentity)
- [Introduction](#introduction)
- [Example](#example)
- [Reusable Responses with Entities](#reusable-responses-with-entities)
- [Defining Entities](#defining-entities)
- [Basic Exposure](#basic-exposure)
- [Exposing with a Presenter](#exposing-with-a-presenter)
- [Conditional Exposure](#conditional-exposure)
- [Safe Exposure](#safe-exposure)
- [Nested Exposure](#nested-exposure)
- [Collection Exposure](#collection-exposure)
- [Merge Fields](#merge-fields)
- [Runtime Exposure](#runtime-exposure)
- [Unexpose](#unexpose)
- [Overriding exposures](#overriding-exposures)
- [Returning only the fields you want](#returning-only-the-fields-you-want)
- [Aliases](#aliases)
- [Format Before Exposing](#format-before-exposing)
- [Expose Nil](#expose-nil)
- [Default Value](#default-value)
- [Documentation](#documentation)
- [Options Hash](#options-hash)
- [Passing Additional Option To Nested Exposure](#passing-additional-option-to-nested-exposure)
- [Attribute Path Tracking](#attribute-path-tracking)
- [Using the Exposure DSL](#using-the-exposure-dsl)
- [Using Entities](#using-entities)
- [Entity Organization](#entity-organization)
- [Caveats](#caveats)
- [Installation](#installation)
- [Testing with Entities](#testing-with-entities)
- [Project Resources](#project-resources)
- [Contributing](#contributing)
- [License](#license)
- [Copyright](#copyright)
# Grape::Entity
## Introduction
This gem adds Entity support to API frameworks, such as [Grape](https://github.com/ruby-grape/grape). Grape's Entity is an API focused facade that sits on top of an object model.
### Example
```ruby
module API
module Entities
class Status < Grape::Entity
format_with(:iso_timestamp) { |dt| dt.iso8601 }
expose :user_name
expose :text, documentation: { type: "String", desc: "Status update text." }
expose :ip, if: { type: :full }
expose :user_type, :user_id, if: lambda { |status, options| status.user.public? }
expose :location, merge: true
expose :contact_info do
expose :phone
expose :address, merge: true, using: API::Entities::Address
end
expose :digest do |status, options|
Digest::MD5.hexdigest status.txt
end
expose :replies, using: API::Entities::Status, as: :responses
expose :last_reply, using: API::Entities::Status do |status, options|
status.replies.last
end
with_options(format_with: :iso_timestamp) do
expose :created_at
expose :updated_at
end
end
end
end
module API
module Entities
class StatusDetailed < API::Entities::Status
expose :internal_id
end
end
end
```
## Reusable Responses with Entities
Entities are a reusable means for converting Ruby objects to API responses. Entities can be used to conditionally include fields, nest other entities, and build ever larger responses, using inheritance.
### Defining Entities
Entities inherit from Grape::Entity, and define a simple DSL. Exposures can use runtime options to determine which fields should be visible, these options are available to `:if`, `:unless`, and `:proc`.
#### Basic Exposure
Define a list of fields that will always be exposed.
```ruby
expose :user_name, :ip
```
The field lookup takes several steps
* first try `entity-instance.exposure`
* next try `object.exposure`
* next try `object.fetch(exposure)`
* last raise an Exception
`exposure` is a Symbol by default. If `object` is a Hash with stringified keys, you can set the hash accessor at the entity-class level to properly expose its members:
```ruby
class Status < GrapeEntity
self.hash_access = :to_s
expose :code
expose :message
end
Status.represent({ 'code' => 418, 'message' => "I'm a teapot" }).as_json
#=> { code: 418, message: "I'm a teapot" }
```
#### Exposing with a Presenter
Don't derive your model classes from `Grape::Entity`, expose them using a presenter.
```ruby
expose :replies, using: API::Entities::Status, as: :responses
```
Presenter classes can also be specified in string format, which helps with circular dependencies.
```ruby
expose :replies, using: "API::Entities::Status", as: :responses
```
#### Conditional Exposure
Use `:if` or `:unless` to expose fields conditionally.
```ruby
expose :ip, if: { type: :full }
expose :ip, if: lambda { |instance, options| options[:type] == :full } # exposed if the function evaluates to true
expose :ip, if: :type # exposed if :type is available in the options hash
expose :ip, if: { type: :full } # exposed if options :type has a value of :full
expose :ip, unless: ... # the opposite of :if
```
#### Safe Exposure
Don't raise an exception and expose as nil, even if the :x cannot be evaluated.
```ruby
expose :ip, safe: true
```
#### Nested Exposure
Supply a block to define a hash using nested exposures.
```ruby
expose :contact_info do
expose :phone
expose :address, using: API::Entities::Address
end
```
You can also conditionally expose attributes in nested exposures:
```ruby
expose :contact_info do
expose :phone
expose :address, using: API::Entities::Address
expose :email, if: lambda { |instance, options| options[:type] == :full }
end
```
#### Collection Exposure
Use `root(plural, singular = nil)` to expose an object or a collection of objects with a root key.
```ruby
root 'users', 'user'
expose :id, :name, ...
```
By default every object of a collection is wrapped into an instance of your `Entity` class.
You can override this behavior and wrap the whole collection into one instance of your `Entity`
class.
As example:
```ruby
present_collection true, :collection_name # `collection_name` is optional and defaults to `items`
expose :collection_name, using: API::Entities::Items
```
#### Merge Fields
Use `:merge` option to merge fields into the hash or into the root:
```ruby
expose :contact_info do
expose :phone
expose :address, merge: true, using: API::Entities::Address
end
expose :status, merge: true
```
This will return something like:
```ruby
{ contact_info: { phone: "88002000700", city: 'City 17', address_line: 'Block C' }, text: 'HL3', likes: 19 }
```
It also works with collections:
```ruby
expose :profiles do
expose :users, merge: true, using: API::Entities::User
expose :admins, merge: true, using: API::Entities::Admin
end
```
Provide lambda to solve collisions:
```ruby
expose :status, merge: ->(key, old_val, new_val) { old_val + new_val if old_val && new_val }
```
#### Runtime Exposure
Use a block or a `Proc` to evaluate exposure at runtime. The supplied block or
`Proc` will be called with two parameters: the represented object and runtime options.
**NOTE:** A block supplied with no parameters will be evaluated as a nested exposure (see above).
```ruby
expose :digest do |status, options|
Digest::MD5.hexdigest status.txt
end
```
```ruby
expose :digest, proc: ... # equivalent to a block
```
You can also define a method on the entity and it will try that before trying
on the object the entity wraps.
```ruby
class ExampleEntity < Grape::Entity
expose :attr_not_on_wrapped_object
# ...
private
def attr_not_on_wrapped_object
42
end
end
```
You always have access to the presented instance (`object`) and the top-level
entity options (`options`).
```ruby
class ExampleEntity < Grape::Entity
expose :formatted_value
# ...
private
def formatted_value
"+ X #{object.value} #{options[:y]}"
end
end
```
#### Unexpose
To undefine an exposed field, use the ```.unexpose``` method. Useful for modifying inherited entities.
```ruby
class UserData < Grape::Entity
expose :name
expose :address1
expose :address2
expose :address_state
expose :address_city
expose :email
expose :phone
end
class MailingAddress < UserData
unexpose :email
unexpose :phone
end
```
#### Overriding exposures
If you want to add one more exposure for the field but don't want the first one to be fired (for instance, when using inheritance), you can use the `override` flag. For instance:
```ruby
class User < Grape::Entity
expose :name
end
class Employee < User
expose :name, as: :employee_name, override: true
end
```
`User` will return something like this `{ "name" : "John" }` while `Employee` will present the same data as `{ "employee_name" : "John" }` instead of `{ "name" : "John", "employee_name" : "John" }`.
#### Returning only the fields you want
After exposing the desired attributes, you can choose which one you need when representing some object or collection by using the only: and except: options. See the example:
```ruby
class UserEntity
expose :id
expose :name
expose :email
end
class Entity
expose :id
expose :title
expose :user, using: UserEntity
end
data = Entity.represent(model, only: [:title, { user: [:name, :email] }])
data.as_json
```
This will return something like this:
```ruby
{
title: 'grape-entity is awesome!',
user: {
name: 'John Applet',
email: 'john@example.com'
}
}
```
Instead of returning all the exposed attributes.
The same result can be achieved with the following exposure:
```ruby
data = Entity.represent(model, except: [:id, { user: [:id] }])
data.as_json
```
#### Aliases
Expose under a different name with `:as`.
```ruby
expose :replies, using: API::Entities::Status, as: :responses
```
#### Format Before Exposing
Apply a formatter before exposing a value.
```ruby
module Entities
class MyModel < Grape::Entity
format_with(:iso_timestamp) do |date|
date.iso8601
end
with_options(format_with: :iso_timestamp) do
expose :created_at
expose :updated_at
end
end
end
```
Defining a reusable formatter between multiples entities:
```ruby
module ApiHelpers
extend Grape::API::Helpers
Grape::Entity.format_with :utc do |date|
date.utc if date
end
end
```
```ruby
module Entities
class MyModel < Grape::Entity
expose :updated_at, format_with: :utc
end
class AnotherModel < Grape::Entity
expose :created_at, format_with: :utc
end
end
```
#### Expose Nil
By default, exposures that contain `nil` values will be represented in the resulting JSON as `null`.
As an example, a hash with the following values:
```ruby
{
name: nil,
age: 100
}
```
will result in a JSON object that looks like:
```javascript
{
"name": null,
"age": 100
}
```
There are also times when, rather than displaying an attribute with a `null` value, it is more desirable to not display the attribute at all. Using the hash from above the desired JSON would look like:
```javascript
{
"age": 100
}
```
In order to turn on this behavior for an as-exposure basis, the option `expose_nil` can be used. By default, `expose_nil` is considered to be `true`, meaning that `nil` values will be represented in JSON as `null`. If `false` is provided, then attributes with `nil` values will be omitted from the resulting JSON completely.
```ruby
module Entities
class MyModel < Grape::Entity
expose :name, expose_nil: false
expose :age, expose_nil: false
end
end
```
`expose_nil` is per exposure, so you can suppress exposures from resulting in `null` or express `null` values on a per exposure basis as you need:
```ruby
module Entities
class MyModel < Grape::Entity
expose :name, expose_nil: false
expose :age # since expose_nil is omitted nil values will be rendered as null
end
end
```
It is also possible to use `expose_nil` with `with_options` if you want to add the configuration to multiple exposures at once.
```ruby
module Entities
class MyModel < Grape::Entity
# None of the exposures in the with_options block will render nil values as null
with_options(expose_nil: false) do
expose :name
expose :age
end
end
end
```
When using `with_options`, it is possible to again override which exposures will render `nil` as `null` by adding the option on a specific exposure.
```ruby
module Entities
class MyModel < Grape::Entity
# None of the exposures in the with_options block will render nil values as null
with_options(expose_nil: false) do
expose :name
expose :age, expose_nil: true # nil values would be rendered as null in the JSON
end
end
end
```
#### Default Value
This option can be used to provide a default value in case the return value is nil or empty.
```ruby
module Entities
class MyModel < Grape::Entity
expose :name, default: ''
expose :age, default: 60
end
end
```
#### Documentation
Expose documentation with the field. Gets bubbled up when used with Grape and various API documentation systems.
```ruby
expose :text, documentation: { type: "String", desc: "Status update text." }
```
### Options Hash
The option keys `:version` and `:collection` are always defined. The `:version` key is defined as `api.version`. The `:collection` key is boolean, and defined as `true` if the object presented is an array. The options also contain the runtime environment in `:env`, which includes request parameters in `options[:env]['grape.request.params']`.
Any additional options defined on the entity exposure are included as is. In the following example `user` is set to the value of `current_user`.
```ruby
class Status < Grape::Entity
expose :user, if: lambda { |instance, options| options[:user] } do |instance, options|
# examine available environment keys with `p options[:env].keys`
options[:user]
end
end
```
```
present s, with: Status, user: current_user
```
#### Passing Additional Option To Nested Exposure
Sometimes you want to pass additional options or parameters to nested a exposure. For example, let's say that you need to expose an address for a contact info and it has two different formats: **full** and **simple**. You can pass an additional `full_format` option to specify which format to render.
```ruby
# api/contact.rb
expose :contact_info do
expose :phone
expose :address do |instance, options|
# use `#merge` to extend options and then pass the new version of options to the nested entity
API::Entities::Address.represent instance.address, options.merge(full_format: instance.need_full_format?)
end
expose :email, if: lambda { |instance, options| options[:type] == :full }
end
# api/address.rb
expose :state, if: lambda {|instance, options| !!options[:full_format]} # the new option could be retrieved in options hash for conditional exposure
expose :city, if: lambda {|instance, options| !!options[:full_format]}
expose :street do |instance, options|
# the new option could be retrieved in options hash for runtime exposure
!!options[:full_format] ? instance.full_street_name : instance.simple_street_name
end
```
**Notice**: In the above code, you should pay attention to [**Safe Exposure**](#safe-exposure) yourself. For example, `instance.address` might be `nil` and it is better to expose it as nil directly.
#### Attribute Path Tracking
Sometimes, especially when there are nested attributes, you might want to know which attribute
is being exposed. For example, some APIs allow users to provide a parameter to control which fields
will be included in (or excluded from) the response.
GrapeEntity can track the path of each attribute, which you can access during conditions checking
or runtime exposure via `options[:attr_path]`.
The attribute path is an array. The last item of this array is the name (alias) of current attribute.
If the attribute is nested, the former items are names (aliases) of its ancestor attributes.
Example:
```ruby
class Status < Grape::Entity
expose :user # path is [:user]
expose :foo, as: :bar # path is [:bar]
expose :a do
expose :b, as: :xx do
expose :c # path is [:a, :xx, :c]
end
end
end
```
### Using the Exposure DSL
Grape ships with a DSL to easily define entities within the context of an existing class:
```ruby
class Status
include Grape::Entity::DSL
entity :text, :user_id do
expose :detailed, if: :conditional
end
end
```
The above will automatically create a `Status::Entity` class and define properties on it according to the same rules as above. If you only want to define simple exposures you don't have to supply a block and can instead simply supply a list of comma-separated symbols.
### Using Entities
With Grape, once an entity is defined, it can be used within endpoints, by calling `present`. The `present` method accepts two arguments, the `object` to be presented and the `options` associated with it. The options hash must always include `:with`, which defines the entity to expose (unless namespaced entity classes are used, see [next section](#entity-organization)).
If the entity includes documentation it can be included in an endpoint's description.
```ruby
module API
class Statuses < Grape::API
version 'v1'
desc 'Statuses.', {
params: API::Entities::Status.documentation
}
get '/statuses' do
statuses = Status.all
type = current_user.admin? ? :full : :default
present statuses, with: API::Entities::Status, type: type
end
end
end
```
### Entity Organization
In addition to separately organizing entities, it may be useful to put them as namespaced classes underneath the model they represent.
```ruby
class Status
def entity
Entity.new(self)
end
class Entity < Grape::Entity
expose :text, :user_id
end
end
```
If you organize your entities this way, Grape will automatically detect the `Entity` class and use it to present your models. In this example, if you added `present Status.new` to your endpoint, Grape would automatically detect that there is a `Status::Entity` class and use that as the representative entity. This can still be overridden by using the `:with` option or an explicit `represents` call.
### Caveats
Entities with duplicate exposure names and conditions will silently overwrite one another. In the following example, when `object.check` equals "foo", only `field_a` will be exposed. However, when `object.check` equals "bar" both `field_b` and `foo` will be exposed.
```ruby
module API
module Entities
class Status < Grape::Entity
expose :field_a, :foo, if: lambda { |object, options| object.check == "foo" }
expose :field_b, :foo, if: lambda { |object, options| object.check == "bar" }
end
end
end
```
This can be problematic, when you have mixed collections. Using `respond_to?` is safer.
```ruby
module API
module Entities
class Status < Grape::Entity
expose :field_a, if: lambda { |object, options| object.check == "foo" }
expose :field_b, if: lambda { |object, options| object.check == "bar" }
expose :foo, if: lambda { |object, options| object.respond_to?(:foo) }
end
end
end
```
Also note that an `ArgumentError` is raised when unknown options are passed to either `expose` or `with_options`.
## Installation
Add this line to your application's Gemfile:
gem 'grape-entity'
And then execute:
$ bundle
Or install it yourself as:
$ gem install grape-entity
## Testing with Entities
Test API request/response as usual.
Also see [Grape Entity Matchers](https://github.com/agileanimal/grape-entity-matchers).
## Project Resources
* Need help? [Grape Google Group](http://groups.google.com/group/ruby-grape)
## Contributing
See [CONTRIBUTING.md](CONTRIBUTING.md).
## License
MIT License. See [LICENSE](LICENSE) for details.
## Copyright
Copyright (c) 2010-2016 Michael Bleigh, Intridea, Inc., ruby-grape and Contributors.