Module: Sequel::Plugins::JsonSerializer

Defined in:
lib/sequel/plugins/json_serializer.rb

Overview

The json_serializer plugin handles serializing entire Sequel::Model objects to JSON, as well as support for deserializing JSON directly into Sequel::Model objects. It requires the json library, and can work with either the pure ruby version or the C extension.

Basic Example:

album = Album[1]
album.to_json
# => '{"id"=>1,"name"=>"RF","artist_id"=>2}'

In addition, you can provide options to control the JSON output:

album.to_json(only: :name)
album.to_json(except: [:id, :artist_id])
# => '{"json_class"="Album","name"=>"RF"}'

album.to_json(include: :artist)
# => '{"id":1,"name":"RF","artist_id":2,
#      "artist":{"id":2,"name":"YJM"}}'

You can use a hash value with :include to pass options to associations:

album.to_json(include: {artist: {only: :name}})
# => '{"id":1,"name":"RF","artist_id":2,
#      "artist":{"name":"YJM"}}'

You can specify a name for a given association by using an aliased expression as the key in the :include hash

album.to_json(include: {Sequel.as(:artist, :singer)=>{only: :name}})
# => '{"id":1,"name":"RF","artist_id":2,
#      "singer":{"name":"YJM"}}'

You can specify the :root option to nest the JSON under the name of the model:

album.to_json(root: true)
# => '{"album":{"id":1,"name":"RF","artist_id":2}}'

You can specify JSON serialization options to use later:

album.json_serializer_opts(root: true)
[album].to_json
# => '[{"album":{"id":1,"name":"RF","artist_id":2}}]'

Additionally, to_json also exists as a class and dataset method, both of which return all objects in the dataset:

Album.to_json
Album.where(artist_id: 1).to_json(include: :tags)

If you have an existing array of model instances you want to convert to JSON, you can call the class to_json method with the :array option:

Album.to_json(array: [Album[1], Album[2]])

All to_json methods take blocks, and if a block is given, it will yield the array or hash before serialization, and will serialize the value the block returns. This allows you to customize the resulting JSON format on a per-call basis.

In addition to creating JSON, this plugin also enables Sequel::Model classes to create instances directly from JSON using the from_json class method:

json = album.to_json
album = Album.from_json(json)

The array_from_json class method exists to parse arrays of model instances from json:

json = Album.where(artist_id: 1).to_json
albums = Album.array_from_json(json)

These does not necessarily round trip, since doing so would let users create model objects with arbitrary values. By default, from_json will call set with the values in the hash. If you want to specify the allowed fields, you can use the :fields option, which will call set_fields with the given fields:

Album.from_json(album.to_json, fields: %w'id name')

If you want to update an existing instance, you can use the from_json instance method:

album.from_json(json)

Both of these allow creation of cached associated objects, if you provide the :associations option:

album.from_json(json, associations: :artist)

You can even provide options when setting up the associated objects:

album.from_json(json, associations: {artist: {fields: %w'id name', associations: :tags}})

Note that active_support/json makes incompatible changes to the to_json API, and breaks some aspects of the json_serializer plugin. You can undo the damage done by active_support/json by doing:

class Array
  def to_json(options = {})
    JSON.generate(self)
  end
end

class Hash
  def to_json(options = {})
    JSON.generate(self)
  end
end

Note that this will probably cause active_support/json to no longer work correctly in some cases.

Usage:

# Add JSON output capability to all model subclass instances (called before loading subclasses)
Sequel::Model.plugin :json_serializer

# Add JSON output capability to Album class instances
Album.plugin :json_serializer

Defined Under Namespace

Modules: ClassMethods, DatasetMethods, InstanceMethods Classes: Literal

Class Method Summary collapse

Class Method Details

.configure(model, opts = OPTS) ⇒ Object

Set up the column readers to do deserialization and the column writers to save the value in deserialized_values.



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# File 'lib/sequel/plugins/json_serializer.rb', line 134

def self.configure(model, opts=OPTS)
  model.instance_exec do
    @json_serializer_opts = (@json_serializer_opts || OPTS).merge(opts)
  end
end