SimpleAMS

by vasilakisfil

vasilakisfil / SimpleAMS

Modern Ruby serializers

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SimpleAMS

"Simple things should be simple and complex things should be possible." Alan Kay.

If we want to interact with modern APIs we should start building modern, flexible libraries that help developers to build such APIs. Modern Ruby serializers, as I always wanted them to be.

You can find the core ideas, the reasoning behind the architecture, use cases and examples here.

Table of contents

  1. Installation
  2. Usage
  3. Development
  4. Contributing

Installation

Add this line to your application's Gemfile:

gem 'simple_ams'

And then execute:

$ bundle

Or install it yourself as:

$ gem install simple_ams

Usage

The gem's interface has been inspired by ActiveModel Serializers 0.9.2, 0.10.stable, jsonapi-rb and Ember Data. However, it has been built for POROs, has zero dependencies and does not relate to Rails in any case other than some nostalgia for the (advanced at that time) pre-0.10 ActiveModel Serialiers.

You can find the core ideas, the reasoning behind the architecture, use cases and examples here.

Simple case

You will rarely need all the advanced options. Usually you will have something like that:

class UserSerializer
  include SimpleAMS::DSL

#specify the adapter we want to use adapter SimpleAMS::Adapters::JSONAPI

#specify the attributes we want to serialize from the given object attributes :id, :name, :email, :created_at, :role

#specify the type of the resource type :user #specify the name of the collection collection :users

#specify a relation. Here microposts serves as both a name of the collection #and the name of the method used to retrieve the values of the collection #from the given object has_many :microposts end

Rendering a resource

Then you can just feed your serializer with data:

SimpleAMS::Renderer.new(user).to_json

to_json
first calls
as_json
, which creates a ruby Hash and then
to_json
is called on top of that hash.

If you want to filter the available options (defined by the serializer) when you instantiate the serializer,

Renderer
accepts an options hash. In there you can throw pretty much the same DSL:
SimpleAMS::Renderer.new(user, {
  serializer: UserSerializer, fields: [:id, :name, :email], includes: []
}).to_json

Here we say that we only want 3 specific fields, and no relations at all.

Rendering a collection

Rendering a collection is pretty similar, meaning that it reuses the same serializer class, and accepts the same runtime options. The only difference is that you need to call a different class.

SimpleAMS::Renderer::Collection.new(users, {
  serializer: UserSerializer, fields: [:id, :email, :name], includes: []
}).to_json

Serializer DSL

The serializer is a very robust, yet simple, with a hash-based internal representation.

fields directive

Fields specify the attributes that the serializer will hold. The values of each attribute is taken by the to-be serialized object, unless the serializer has a method of the same name.

fields :id, :name, :email, :created_at, :role

Using

attributes
is also valid, it’s just an alias after all:
attributes :id, :name, :email, :created_at, :role

Of course, any field can be overridden by defining a method of the same name inside the serializer. In there, you can have access to a method called object which holds the actual resource to be serialized:

def name
  "#{object.first_name} #{object.last_name}"
end

Relations (hasmany/hasone/belongs_to)

These directives allows you to append relations in a resource.

has_one
is just an alias of
belongs_to
since there is no real difference in APIs (although internally and in adapters, SimpleAMS knows if you specified the relation using
belongs_to
or
has_one
, making it future proof in case API specs decide to support each one in a different way).
has_many :microposts

Again, it can be overridden by defining a method of the same name:

def microposts
  Post.where(user_id: object.id).order(:created_at, :desc).limit(10)
end
relations are recursive

The relations directives can take the same options as the rendering.

#overriding the serializer
has_many :microposts, serializer: CustomPostsSerializer
#overriding the serializer and fields that should be included
has_many :microposts, serializer: CustomPostsSerializer, fields: [:content]
#overriding the serializer, fields and relations that should be included
has_many :microposts, serializer: CustomPostsSerializer, fields: [:content],
  includes: []
#overriding the serializer, fields, relations and links
has_many :microposts, serializer: CustomPostsSerializer, fields: [:content],
  includes: [], links: [:self]

When overriding from the relations directives (or when rendering in general) you are able to override any directive defined in the serializer to acquire a subset but never a superset.

embedded content (again recursive)

Sometimes, an annoying spec might define parts of a relation in the main body, while parts of the relation somewhere else. For instance, JSON:API does that by having some links in the main body and the rest in the included section. That’s also possible if you pass a block in the relation directive:

has_many :microposts, serializer: MicropostsSerializer, fields: [:content] do
  #these goes to a class named `Embedded`, attached to the relation
  link :self, ->(obj){ "/api/v1/users/#{obj.id}/relationships/microposts" }
  link :related, ->(obj){ ["/api/v1/users/1", rel: :user] }
end

Inside that block, you can pass any parameter the original DSL supports and will be stored in an Embedded class under MicropostsSerializer. Btw SimpleAMS is smart enough (one of the very few cases that acts like that) to figure out that if a lambda returns something that’s not an array, then this must be the value, while options are just empty.

relation name/type

Sometimes, we want to detach the relation’s name from the type. In the previous example

microposts
is the relation name (whatever that means), while the type is defined by the
MicropostsSerializer
, unless we override it, which can be done either in the relation serializer itself, or when we use the relation from the parent serializer:
has_many :microposts, serializer: MicropostsSerializer, fields: [:content], type: :feed do
  link :self, ->(obj){ "/api/v1/users/#{obj.id}/relationships/microposts" }
  link :related, ->(obj){ ["/api/v1/users/1", rel: :user] }
end

Internally SimpleAMS, differentiates type from name, and usually type is something that’s semantically stronger (like a relation type) than name. You can even inject the name of the relation using the name option:

has_many :microposts, serializer: MicropostsSerializer, fields: [:content], type: :feed, name: :posts do
  link :self, ->(obj){ "/api/v1/users/#{obj.id}/relationships/microposts" }
  link :related, ->(obj){ ["/api/v1/users/1", rel: :user] }
end

As I said, the name, which is usually the name of the attribute that includes the relation in the JSON format, doesn’t really have any semantic meaning in most specs. At least I haven’t seen any spec to depend on the root attribute name of the relation. Instead it’s the type that’s important, because type is what the web linking RFC defines.

value-hashmap type of directives

These are directives like adapter. They take a value, and optionally a hashmap, which are options to be passed down straight to the adapter, hence they are adapter specific. Such options are

primary_id
,
type
and
adapter

For instance, for adapter it could be:

ruby
adapter SimpleAMS::Adapters::JSONAPI, root: true

Of course, since we are talking about Ruby here, it would be a huge restriction to not allow dynamic value/hashmap combination. Basically any such directive can accept a lambda (generally anything that responds to

call
) and should return an array where the first part is the value and (optionally) the second part is the options. There is an argument that is passed down to the function/lambda, and that’s the actual object. For instance, to support polymorphic resources you can have the type dynamic:
type ->(obj, s){ obj.employee? ? [:employee, {}] : [:user, {}]}

One of the very few times that SimpleAMS acts smart is inside the lambda, that if you have only a value (not an Array), it will take that as the value, while the options will be taken by the second argument, after the lambda. So the above is equivalent with:

type ->(obj, s){ obj.employee? ? :employee : :user}, {}

Note: you shouldn't use that in case of adapter, as that's the definition of UB :P

adapter

Specifies the adapter to be used. The adapter method is the only one that does not support lambda as it's value, as that would be the definition of undefined behavior. If you want to support polymorphic collections, you should use the type instead in combination with the serializer.

#without options
adapter SimpleAMS::Adapters::JSONAPI
#with adapter-specific options
adapter SimpleAMS::Adapters::JSONAPI, {root: false}

Note that you can even specify your own adapter. Usually you will want to inherit from an existing adapter (like SimpleAMS::Adapters::AMS), but that's not a requirement. All you need is to duck type to 2 methods:

  • initialize(document, options = {}) be able to accept 2 arguments when your adapter is instantiated. The first one is a document, while the second one is the adapter-specific options (like the {root: false}.
  • as_json method returns that returns the hash representation of the serialized result

The conversion of a Hash into raw JSON string is out of the scope of this library. But you will probably want to use the fastest implementation possible like oj.

primary_id

Specifies the primary_id to be used. There are many API specs that handle the identifier of a resource in a different way than the rest of the attributes. JSON:API is one of those.

#without options
primary_id :id
#with adapter-specific options
adapter :id, {external: true}
#dynamic
adapter ->(obj, s) { [obj.class.primary_key, {}]}
type

Specifies the type to be used. There are many API specs that handle the type of a resource in a different way than the rest of the attributes. JSON:API is one of those.

#without options
type :user
#with adapter-specific options
type :user, {polymorphic: false}
#dynamic
type ->(obj, s){ obj.employee? ? [:employee, {}] : [:user, {}]}

name-value-hashmap type of directives

These are similar to the above, only that they also have an actual value, which is converted to a representation through the adapter. Such options are

link
,
meta
,
form
and the most generic directive
generic
.

For instance, think about a links. According to RFC 8288, a link has

  • a link context,
  • a link relation type,
  • a link target, and
  • optionally, target attributes

Now, if we wanted to translate that to our serializers, a link could look like:

ruby
link :feed, '/api/v1/me/feed', {style: :compact}

Here obviously the link context is the serializer itself, the link relation is the feed, and the value is

/api/v1/me/feed
. Now you might say, feed should be the name of the link which is different from the relation type. The relation type could be
microposts
. And actually, that’s the case for JSONAPI v1.1. In that case, the feed should be treated barely as a name (whatever that means) and relation type will be put inside the link options like:
link :feed, '/api/v1/me/feed', {rel: :microposts, style: :compact}

Note however that this needs to be supported by the adapter you are using.

Similar to the case of value-hash directives, it is possible to have dynamic value and options:

#values can be dynamic through lambdas
#lambdas take arguments the object to be serialized and the instantiated serializer
link :feed, ->(obj, s) { [s.api_v1_user_feed_path(user_id: obj.id), {rel: :feed} }
#if the value inside the lambda is single (no array), the options will be taken from
#the second argument, after the lambda. So the above is equivelent to:
link :feed, ->(obj, s) { s.api_v1_user_feed_path(user_id: obj.id) }, rel: :feed
link

Specifies a link to be used. There are many API specs that handle the links of a resource in a special way (JSON:API is one of those). You can specify multiple links, as long as each link name is unique.

#specifying a link with without options
link :feed, "/api/v1/feed"
#specifying a link with options
link :feed, "/api/v1/feed", {rel: :feed, compact: true}
#values can be dynamic through lambdas
#lambdas take arguments the object to be serialized and the instantiated serializer
link :feed, ->(obj, s) { [s.api_v1_user_feed_path(user_id: obj.id), {rel: :feed, compact: true}] }
#if the value inside the lambda is single (no array), the options will be taken from
#the second argument, after the lambda. So the above is equivelent to:
link :feed, ->(obj, s) { s.api_v1_user_feed_path(user_id: obj.id) }, rel: :feed, compact: true
meta

Specifies a meta to be used. There are many API specs that handle the metas of a resource in a special way (JSON:API is one of those). You can specify multiple metas, as long as each link name is unique.

#specifying a meta with without options
meta :total_count, 1
#specifying a meta with options
meta :total_count, 1, {compact: true}
#values can be dynamic through lambdas
#lambdas take arguments the object to be serialized and the instantiated serializer
#in this case an object is apparently a collection/array
meta :total_count, ->(obj, s) { [obj.count, {compact: true}] }
#if the value inside the lambda is single (no array), the options will be taken from
#the second argument, after the lambda. So the above is equivelent to:
meta :total_count, ->(obj, s) { obj.count }, {compact: true}
form

Specifies a form to be used. Unfortunately, there are very few API specs that handle forms (the Ion hypermedia type is one of those). You can specify multiple forms, as long as each link name is unique.

#specifying a form with without options
form :upload, {method: :get, url: "/api/v1/submit"}
#specifying a form with options
form :upload, {method: :get, url: "/api/v1/submit"}, compact: true
#values can be dynamic through lambdas
#lambdas take arguments the object to be serialized and the instantiated serializer
form :upload, ->(obj, s) { [obj.class.upload_form_options, {compact: true}] }
#if the value inside the lambda is single (no array), the options will be taken from
#the second argument, after the lambda. So the above is equivelent to:
form :upload, ->(obj, s) { obj.class.upload_form_options }, {compact: true}
generic

Specifies a generic to be used. A generic is just a placeholder for extensions that are unknown to SimpleAMS (but maybe they make a lot of sense to you ^_^)

#specifying a generic with without options
generic :pagination, :extended
#specifying a form with options
generic :pagination, :extended, compact: false
#values can be dynamic through lambdas
#lambdas take arguments the object to be serialized and the instantiated serializer
generic :pagination, ->(obj, s) { [obj.class.pagination_type, {compact: false}] }
#if the value inside the lambda is single (no array), the options will be taken from
#the second argument, after the lambda. So the above is equivelent to:
generic :pagination, ->(obj, s) { obj.class.pagination_type }, {compact: false}
group of links/metas/forms/generics

Each of the aforementioned options comes with a plural form as well. For instance, if we want to specify multiple

links
at the same time:
links {
  self: ['/api/v1/me', {rel: :user}]
  feed: ['/api/v1/me/feed', {rel: :feed}]
}

or if we want to specify multiple

metas
:
ruby
metas {
  total_count: ->(obj){ obj.count }
  pages: ->(obj){ obj.pages_count }
}

Same goes for

forms
and
generics
.

collection directive

SimpleAMS has a unique ability to allow you specify different options when you are rendering a collection. In its most simple use case it specified the plural name of the resource, used when rendering a collection:

collection :users

It’s needed, if your adapter serializes the collection using a root element. But it can do much more than that: it allows you to define directives on the collection level. For instance, if you want to have a link that should be applied only to the collection level and not to each resource of the collection, then you need to define it inside the collection’s block:

collection :users do
  link :self, "/api/v1/users"
end

Or if we also want to have the total count of the collection, that should go in there actually:

collection :users do
  link :self, "/api/v1/users"
  meta :count, ->(collection, s) { collection.count }
end

Again, inside that block you can define using the regular DSL, whatever you would define in the resource level. It’s just yet another level of recursion since, the same things that I show you here can be applied in the collection level inside the block. For instance, in theory (and if the adapter supports it), you can specify relations that apply only to the collection level:

class UserSerializer
  include SimpleAMS::DSL

adapter SimpleAMS::Adapters::JSONAPI

attributes :id, :name, :email, :created_at, :role

type :user collection :users do link :self, "/api/v1/users" meta :count, ->(collection, s) { collection.count }

has_one :s3_uploader #whatever that means :P

end

has_many :microposts end

Rendering DSL

When rendering a resource, it should be straightforward:

SimpleAMS::Renderer.new(user, { serializer: UserSerializer }).to_json

All you need is to specify a serializer. In the example above, the resulted resource is a reflection of what is defined inside the serializer. However, the serializer acts as a filtering mechanism, meaning that you can override anything the serializer defines, given that the result creates a subset and not a superset (any superset options will be ignored).

For instance, you can override the type during rendering:

SimpleAMS::Renderer.new(user, {
  serializer: UserSerializer, type: :person
}).to_json

or you can override the relations, and specify that you don’t want to include any relation defined in the serializer:

SimpleAMS::Renderer.new(user, {
  serializer: UserSerializer, includes: []
}).to_json

or specify exactly what fields you want:

SimpleAMS::Renderer.new(user, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at]
}).to_json

or even specify the links subset that you want:

SimpleAMS::Renderer.new(user, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at],
  links: [:self, :comments, :posts]
}).to_json

and the list goes on.. basically the rendering DSL is identical

includes vs relations

There might be some confusion between

includes
and
relations
, so to clear things up: *
includes
: specifies which relations you want to include, out of the available relations. *
relations
: specifies the available relations, so it's not just an array of symbols, but rather full relation objects which are generated through the dsl. The raw representation of relations is an array of objects where each object is
[relation_type, name, options, embedded_options]
. Here
relation_type
is the type of the relation (
has_many
,
belongs_to
etc),
name
is the name of the relation (like users),
options
, any relation options, and
embedded_options
relevant to embedded options.

So when rendering, if you don't want any relations at all, the correct way is to specify

includes: []
. In practice you can use
relations: []
as well, but that will mean that the serializer has no relations at all (takes precedence over
includes
). But that's not the correct way to do it. For instance, thing about another scenario: you want to specify only one relation, the
feed
relation. With
includes
you would have
includes: [:feed]
. With relations, you would have to specify the relation at runtime (
relations: [[:has_one, :feed, {serializer: FeedSerializer, fields: [:id, :content]}, {}]]
) and then also specify that you only want that:
includes: [:feed]
.

In general, there is no reason why you should use

relations
at rendering time, instead you should leave that to the serializer, and only specify the
includes
.

Btw you might have noticed

includes
only as a rendering option, but SimpleAMS DSL is used all over the place, and actually it's a serializer option as well (just that it's not very useful ^_^).

Rendering collections

Rendering a collection is similar, only that you need to call

SimpleAMS::Renderer::Collection
instead of just
SimpleAMS::Renderer
:
SimpleAMS::Renderer::Collection.new(users, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at],
  links: [:self, :comments, :posts]
}).to_json

Note that even with collection, by default everything goes to the resource. If you need to specify options for the collection itself, you need to use the collection key. For instance, having some metas inside the collection:

SimpleAMS::Renderer::Collection.new(users, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at],
  links: [:self, :comments, :posts],
  collection: {
    metas: [:total_count]
  }
}).to_json

Rendering options with values

If you want to specify the actual values when rendering the resource, rather than taking into account the serializer, you can inject a hashmap:

SimpleAMS::Renderer::Collection.new(users, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at],
  links: [:self, :comments, :posts],
  collection: {
    metas: {
      total_count: users.count,
  }
}).to_json

Of course, you can also pass a lambda there, but not sure what’s the point since the lambda parameter is the resource that you already try to render so it’s not going to give you anything more (and will be slower actually).

Exposing methods inside the serializer, like helpers

When rendering you can expose a couple of objects in the serializer:

SimpleAMS::Renderer::Collection.new(users, {
  serializer: UserSerializer, fields: [:id, :email, :name, :created_at],
  #exposing helpers that will be available inside the serializer
  expose: {
    #a class
    current_user: User.first
    #or a module
    helpers: CommonHelpers
  },
}).to_json

The expose attribute is also available through DSL, although usually that’s not very useful. Just wanted to mentions that there is actually parity on everything, since everything has been built on the same building blocks :)

Extended DSL show off

Here is an extended example of the DSL. It's not a real use case of course, but shows what's possible with SimpleAMS and its powerful DSL.

{
  #the primary id of the record(s), used mostly by the underlying adapter (like JSONAPI)
  primary_id: :id,
  #the type of the record, used mostly by the underlying adapter (like JSONAPI)
  type: :user,
  #which relations should be included
  includes: [:posts, videos: [:comments]],
  #which fields for each relation should be included
  fields: [:id, :name, posts: [:id, :text], videos: [:id, :title, comments: [:id, :text]]] #overrides includes when association is specified
  relations: [
    [:belongs_to, :company, {
        serializer: CompanySerializer,
        fields: Company.column_names.map(&:to_sym)
      }
    ],
    [:has_many, :followers, {
        serializer: UserSerializer,
        fields: User.column_names.map(&:to_sym)
      }
    ],
  ]
  #the serializer that should be used
  #makes sense to use it when initializing the Renderer
  serializer: UserSerializer,
  #can also be a lambda, in case of polymorphic records, ideal for ArrayRenderer
  serializer: ->(obj, s){ obj.employee? ? EmployeeSerializer : UserSerializer }
  #specifying the underlying adapter. This cannot be a lambda in case of ArrayRenderer,
  #but can take some useful options that are passed down straight to the adapter class.
  adapter: SimpleAMS::Adapters::AMS, root: true
  #the links data
  links: {
    #can be a simple string
    root: '/api/v1'
    #a string with some options (relation and target attributes as defined by RFC8288
    #however, you can also pass adapter-specific attributes
    posts: "/api/v1/posts/", rel: :posts,
    #it can also be a lambda that takes the resource to be rendered as a param
    #when the lambda is called, it should return the array structure above
    self: ->(obj, s) { ["/api/v1/users/#{obj.id}", rel: :user] }
  },
  #the meta data, same as the links data (available in adapters even for single records)
  metas: {
    type: ->(obj, s){ obj.employee? ? :employee : :user}
    #meta can take arbitrary options as well
    authorization: :oauth, type: :bearer_token
  },
  #the form data, same as the links/metas data (available in adapters even for single records)
  forms: {
    update: ->(obj, s){ User::UpdateForm.for(obj)}
    follow: ->(obj, s){ User::FollowForm.for(obj)}
  },
  #collection parameters, used only in ArrayRenderer
  collection: {
    links: {
      root: '/api/v1'
    },
    metas: {
      pages: ->(obj, s) { [obj.pages, collection: true]},
      current_page: ->(obj, s) { [obj.current_page, collection: true] },
      previous_page: ->(obj, s) { [obj.previous_page, collection: true] },
      next_page: ->(obj, s) { [obj.next_page, collection: true] },
      max_per_page: 50,
    },
    #creating a resource goes in the collection route (users/), hence inside collection options ;)
    forms: {
      create: ->(obj){ User::CreateForm.for(obj)}
    },
  }
  #exposing helpers that will be available inside the seriralizer
  expose: {
    #a class
    current_user: User.first
    #or a module
    helpers: CommonHelpers
  },
}

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.

Contributing

But reports are very welcome at https://github.com/vasilakisfil/SimpleAMS. Please add as much info as you can (serializer and Renderer input) so that we can easily track down the bug.

Pull requests are also very welcome on GitHub at https://github.com/vasilakisfil/SimpleAMS. However, to keep the code's sanity (AMS I am looking to you), I will be very picky on the code style and design, to match (my) existing code characteristics. Because at the end of the day, it's gonna be me who will maintain this thing.

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