Add docs for links (#1909)

Add docs for links

Add docs for links

Add docs for links

Add docs for links

Add docs for links

Add controller info

Grammar fixing

Improve docs

some small wording changes

Add pr to changelog

CHANGELOG.md

@@ -28,6 +28,7 @@ Misc:
 - [#1878](https://github.com/rails-api/active_model_serializers/pull/1878) Cache key generation for serializers now uses `ActiveSupport::Cache.expand_cache_key` instead of `Array#join` by default and is also overridable. This change should be backward-compatible. (@markiz)
 
 - [#1799](https://github.com/rails-api/active_model_serializers/pull/1799) Add documentation for setting the adapter. (@ScottKbka)
+- [#1909](https://github.com/rails-api/active_model_serializers/pull/1909) Add documentation for relationship links. (@vasilakisfil, @NullVoxPopuli)
 
 ### [v0.10.2 (2016-07-05)](https://github.com/rails-api/active_model_serializers/compare/v0.10.1...v0.10.2)
 

docs/README.md

@@ -24,6 +24,7 @@ This is the documentation of ActiveModelSerializers, it's focused on the **0.10.
 
 - [How to add root key](howto/add_root_key.md)
 - [How to add pagination links](howto/add_pagination_links.md)
+- [How to add relationship links](howto/add_relationship_links.md)
 - [Using ActiveModelSerializers Outside Of Controllers](howto/outside_controller_use.md)
 - [Testing ActiveModelSerializers](howto/test.md)
 - [Passing Arbitrary Options](howto/passing_arbitrary_options.md)

docs/howto/add_relationship_links.md

@@ -0,0 +1,137 @@
+[Back to Guides](../README.md)
+
+# How to add relationship links
+
+ActiveModelSerializers offers you many ways to add links in your JSON, depending on your needs.
+The most common use case for links is supporting nested resources.
+
+The following examples are without included relationship data (`include` param is empty),
+specifically the following Rails controller was used for these examples:
+
+```ruby
+class Api::V1::UsersController < ApplicationController
+  def show
+    render jsonapi: User.find(params[:id]),
+      serializer: Api::V1::UserSerializer,
+      include: []
+  end
+```
+
+Bear in mind though that ActiveModelSerializers are [framework-agnostic](outside_controller_use.md), Rails is just a common example here.
+
+### Links as an attribute of a resource
+**This is applicable to JSONAPI, JSON and Attributes adapters**
+
+You can define an attribute in the resource, named `links`.
+
+```ruby
+class Api::V1::UserSerializer < ActiveModel::Serializer
+  attributes :id, :name, :links
+
+  def links
+    {
+      self: api_v1_user_path(object.id),
+      microposts: api_v1_microposts_path(user_id: object.id)
+    }
+  end
+end
+```
+
+This will resilt in (example is in jsonapi adapter):
+```json
+{
+  "data": {
+    "id": "1",
+    "type": "users",
+    "attributes": {
+      "name": "Example User",
+      "links": {
+        "self": "/api/v1/users/1",
+        "microposts": "/api/v1/microposts?user_id=1"
+      }
+    }
+  }
+}
+```
+
+
+### Links as a property of the resource definiton
+**This is only applicable to JSONAPI adapter**
+
+You can use the `links` class method to define the links you need in the resource's primary data.
+
+```ruby
+class Api::V1::UserSerializer < ActiveModel::Serializer
+  attributes :id, :name
+
+  link(:self) { api_v1_user_path(object.id) }
+  link(:microposts) { api_v1_microposts_path(user_id: object.id) }
+end
+```
+
+This will resilt in (example is in jsonapi adapter):
+```json
+{
+  "data": {
+    "id": "1",
+    "type": "users",
+    "attributes": {
+      "name": "Example User"
+    },
+    "links": {
+      "self": "/api/v1/users/1",
+      "microposts": "/api/v1/microposts?user_id=1"
+    }
+  }
+}
+```
+
+### Links that follow the JSONAPI spec
+**This is only applicable to JSONAPI adapter**
+
+If you have a JSONAPI-strict client that you are working with (like `ember-data`)
+you need to construct the links inside the relationships. Also the link to fetch the
+relationship data must be under the `related` attribute, whereas to manipulate the
+relationship (in case of many-to-many relationship) must be under the `self` attribute.
+
+You can find more info in the [spec](http://jsonapi.org/format/#document-resource-object-relationships).
+
+Here is how you can do this:
+
+```ruby
+class Api::V1::UserSerializer < ActiveModel::Serializer
+  attributes :id, :name
+
+  has_many :microposts, serializer: Api::V1::MicropostSerializer do
+    link(:related) { api_v1_microposts_path(user_id: object.id) }
+  end
+
+  #this is needed to avoid n+1, gem core devs are working to remove this necessity
+  #more on: https://github.com/rails-api/active_model_serializers/issues/1325
+  def microposts
+    object.microposts.loaded ? object.microposts : object.microposts.none
+  end
+end
+```
+
+This will result in:
+
+```json
+{
+  "data": {
+    "id": "1",
+    "type": "users",
+    "attributes": {
+      "name": "Example User"
+    },
+    "relationships": {
+      "microposts": {
+        "data": [],
+        "links": {
+          "related": "/api/v1/microposts?user_id=1"
+        }
+      }
+    }
+  }
+}
+```