Add docs for deserialization.

docs/README.md

@@ -13,6 +13,7 @@ This is the documentation of ActiveModelSerializers, it's focused on the **0.10.
 - [Rendering](general/rendering.md)
 - [Caching](general/caching.md)
 - [Logging](general/logging.md)
+- [Deserialization](general/deserialization.md)
 - [Instrumentation](general/instrumentation.md)
 - [JSON API Schema](jsonapi/schema.md)
 - [ARCHITECTURE](ARCHITECTURE.md)

docs/general/deserialization.md

@@ -0,0 +1,100 @@
+[Back to Guides](../README.md)
+
+# Deserialization
+
+This is currently an *experimental* feature. The interface may change.
+
+## JSON API
+
+The `ActiveModelSerializers::Deserialization` defines two methods (namely `jsonapi_parse` and `jsonapi_parse!`), which take a `Hash` or an instance of `ActionController::Parameters` representing a JSON API payload, and return a hash that can directly be used to create/update models. The bang version throws an `InvalidDocument` exception when parsing fails, whereas the "safe" version simply returns an empty hash.
+
+- Parameters
+  - document: `Hash` or `ActionController::Parameters` instance
+  - options:
+    - only: `Array` of whitelisted fields
+    - except: `Array` of blacklisted fields
+    - keys: `Hash` of fields the name of which needs to be modified (e.g. `{ :author => :user, :date => :created_at }`)
+
+Examples:
+
+```ruby
+class PostsController < ActionController::Base
+  def create
+    Post.create(create_params)
+  end
+
+  def create_params
+    ActiveModelSerializers::Deserialization.jsonapi_parse(params, only: [:title, :content, :author])
+  end
+end
+```
+
+
+
+Given a JSON API document,
+
+```
+document = {
+  data: {
+    id: 1,
+    type: 'post',
+    attributes: {
+      title: 'Title 1',
+      date: '2015-12-20'
+    },
+    associations: {
+      author: {
+        data: {
+          type: 'user',
+          id: 2
+        }
+      },
+      second_author: {
+        data: nil
+      },
+      comments: {
+        data: [{
+          type: 'comment',
+          id: 3
+        },{
+          type: 'comment',
+          id: 4
+        }]
+      }
+    }
+  }
+}
+```
+
+The entire document can be parsed without specifying any options:
+```ruby
+ActiveModelSerializers::Deserialization.jsonapi_parse(document)
+#=>
+# {
+#   title: 'Title 1',
+#   date: '2015-12-20',
+#   author_id: 2,
+#   second_author_id: nil
+#   comment_ids: [3, 4]
+# }
+```
+
+and fields, relationships, and polymorphic relationships can be specified via the options:
+
+```ruby
+ActiveModelSerializers::Deserialization
+  .jsonapi_parse(document, only: [:title, :date, :author],
+                           keys: { date: :published_at },
+                           polymorphic: [:author])
+#=>
+# {
+#   title: 'Title 1',
+#   published_at: '2015-12-20',
+#   author_id: '2',
+#   author_type: 'user'
+# }
+```
+
+## Attributes/Json
+
+There is currently no deserialization for those adapters.