README.md in graphql-relay-0.6.0 vs README.md in graphql-relay-0.6.1

@@ -17,63 +17,287 @@
 bundle install
 ```
 
 ## Usage
 
+`graphql-relay` provides several helpers for making a Relay-compliant GraphQL endpoint in Ruby:
+
+- [global ids](#global-ids) support Relay's UUID-based refetching
+- [connections](#connections) implement Relay's pagination
+- [mutations](#mutations) allow Relay to mutate your system predictably
+
+
 ### Global Ids
 
-Global Ids provide refetching & global identification for Relay.
+Global ids (or UUIDs) provide refetching & global identification for Relay.
 
-You should create `GraphQL::Relay::GlobalNodeIdentification` helper by defining `object_from_id(global_id)` & `type_from_object(object)`. The resulting object provides ID resultion methods, a find-by-global-id field and a node interface. [Example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L9-L18)
+#### UUID Lookup
 
-ObjectTypes should implement that interface with the `global_id_field` helper: [Example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L30-L31)
+Use `GraphQL::Relay::GlobalNodeIdentification` helper by defining `object_from_id(global_id, ctx)` & `type_from_object(object)`. The resulting `NodeIdentification` object is in your schema _and_ internally by `GraphQL::Relay`.
 
-You should attach the field to your query type: [Example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L121)
 
+```ruby
+NodeIdentification = GraphQL::Relay::GlobalNodeIdentification.define do
+  # Given a UUID & the query context,
+  # return the corresponding application object
+  object_from_id -> (id, ctx) do
+    type_name, id = NodeIdentification.from_global_id(id)
+    # "Post" -> Post.find(id)
+    Object.const_get(type_name).find(id)
+  end
+
+  # Given an application object,
+  # return a GraphQL ObjectType to expose that object
+  type_from_object -> (object) do
+    if object.is_a?(Post)
+      PostType
+    else
+      CommentType
+    end
+  end
+end
+```
+
+#### UUID fields
+
+ObjectTypes in your schema should implement `NodeIdentification.interface` with the `global_id_field` helper, for example:
+
+```ruby
+PostType = GraphQL::ObjectType.define do
+  name "Post"
+  interfaces [NodeIdentification.interface]
+  # `id` exposes the UUID
+  global_id_field :id
+
+  # ...
+end
+```
+
+#### `node` field (find-by-UUID)
+
+You should also add a field to your root query type for Relay to re-fetch objects:
+
+```ruby
+QueryType = GraphQL::ObjectType.define do
+  name "Query"
+  # Used by Relay to lookup objects by UUID:
+  field :node, field: NodeIdentification.field
+
+  # ...
+end
+```
+
 ### Connections
 
-Connections will provide arguments, pagination and `pageInfo` for `Array`s or `ActiveRecord::Relation`s. You can use the `connection` definition helper.
+Connections provide pagination and `pageInfo` for `Array`s or `ActiveRecord::Relation`s.
 
-Then, implement the field. It's different than a normal field:
-  - use the `connection` helper to define it, instead of `field`
-  - Call `#connection_type` on an `ObjectType` for the field's return type (eg, `ShipType.connection_type`)
+#### Connection fields
 
-Examples:
+To define a connection field, use the `connection` helper. For a return type, get a type's `.connection_type`. For example:
 
-- [Connection with custom arguments](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L51-L63)
-- [Connection with a different name than the underlying property](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L77)
+```ruby
+PostType = GraphQL::ObjectType.define do
+  # `comments` field returns a CommentsConnection:
+  connection :comments, CommentType.connection_type
+  # To avoid circular dependencies, wrap the return type in a proc:
+  connection :similarPosts, -> { PostType.connection_type }
 
-You can also add custom fields to connection objects: [Example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L36-L43)
+  # ...
+end
+```
 
-At runtime, `graphql-relay` chooses a connection implementation to expose a collection. `graphql-relay` provides `ArrayConnection` and `RelationConnection`, but you can also provide your own with `BaseConnection.register_connection_implementation`.
+You can also define custom arguments and a custom resolve function for connections, just like other fields:
 
+```ruby
+connection :featured_comments, CommentType.connection_type do
+  # Add an argument:
+  argument :since, types.String
+
+  # Return an Array or ActiveRecord::Relation
+  resolve -> (post, args, ctx) {
+    comments = post.comments.featured
+
+    if args[:since]
+      comments = comments.where("created_at >= ", since)
+    end
+
+    comments
+  }
+end
+```
+
+#### Connection types
+
+You can customize a connection type with `.define_connection`:
+
+```ruby
+PostType.define_connection do
+  field :totalCount do
+    type types.Int
+    # `obj` is the Connection, `obj.object` is the collection of Posts
+    resolve -> (obj, args, ctx) { obj.object.count }
+  end
+end
+```
+
+Now, `PostType.connection_type` will include a `totalCount` field.
+
+#### Connection objects
+
+Maybe you need to make a connection object yourself (for example, to return a connection type from a mutation). You can create a connection object like this:
+
+```
+items = ...   # your collection objects
+args = {}     # stub out arguments for this connection object
+connection_class = GraphQL::Relay::BaseConnection.connection_for_items(items)
+connection_class.new(items, args)
+```
+
+`.connection_for_items` will return RelationConnection or ArrayConnection depending on `items`, then you can make a new connection
+
+#### Custom connections
+
+You can define a custom connection class and add it to `GraphQL::Relay`.
+
+First, define the custom connection:
+
+```ruby
+class SetConnection < BaseConnection
+  # derive a cursor from `item`
+  # (it is used to find next & previous nodes,
+  # so it should include `order`)
+  def cursor_from_node(item)
+    # ...
+  end
+
+  private
+  # apply `#first` & `#last` to limit results
+  def paged_nodes
+    # ...
+  end
+
+  # apply cursor, order, filters, etc
+  # to get a subset of matching objects
+  def sliced_nodes
+    # ...
+  end
+end
+```
+
+Then, register the new connection with `GraphQL::Relay::BaseConnection`:
+
+```ruby
+# When exposing a `Set`, use `SetConnection`:
+GraphQL::Relay::BaseConnection.register_connection_implementation(Set, SetConnection)
+```
+
+At runtime, `GraphQL::Relay` will use `SetConnection` to expose `Set`s.
+
+#### Creating connection fields by hand
+
+If you need lower-level access to Connection fields, you can create them programmatically. Given a `GraphQL::Field` which returns a collection of items, you can turn it into a connection field with `ConnectionField.create`.
+
+For example, to wrap a field with a connection field:
+
+```ruby
+field = GraphQL::Field.new
+# ... define the field
+connection_field = GraphQL::Relay::ConnectionField.create(field)
+```
+
+
 ### Mutations
 
-Mutations allow Relay to mutate your system. When you define a mutation, you'll be defining:
-  - A field for your schema's `mutation` root
-  - A derived `InputObjectType` for input values
-  - A derived `ObjectType` for return values
+Mutations allow Relay to mutate your system. They conform to a strict API which makes them predictable to the client.
 
-You _don't_ define anything having to do with `clientMutationId`. That's automatically created.
+### Mutation root
 
+To add mutations to your GraphQL schema, define a mutation type and pass it to your schema:
+
+```ruby
+# Define the mutation type
+MutationType = GraphQL::ObjectType.define do
+  name "Mutation"
+  # ...
+end
+
+# and pass it to the schema
+MySchema = GraphQL::Schema.new(
+  query: QueryType,
+  mutation: MutationType
+)
+```
+
+Like `QueryType`, `MutationType` is a root of the schema.
+
+### Mutation fields
+
+Members of `MutationType` are _mutation fields_. For GraphQL in general, mutation fields are identical to query fields _except_ that they have side-effects (which mutate application state, eg, update the database).
+
+For Relay-compliant GraphQL, a mutation field must comply to a strict API. `GraphQL::Relay` includes a mutation definition helper (see below) to make it simple.
+
+After defining a mutation (see below), add it to your mutation type:
+
+```ruby
+MutationType = GraphQL::ObjectType.define do
+  name "Mutation"
+  # Add the mutation's derived field to the mutation type
+  field :addComment, field: AddCommentMutation.field
+  # ...
+end
+```
+
+### Relay mutations
+
 To define a mutation, use `GraphQL::Relay::Mutation.define`. Inside the block, you should configure:
   - `name`, which will name the mutation field & derived types
   - `input_field`s, which will be applied to the derived `InputObjectType`
   - `return_field`s, which will be applied to the derived `ObjectType`
-  - `resolve(-> (inputs, ctx))`, the mutation which will actually happen
+  - `resolve(-> (inputs, ctx) { ... })`, the mutation which will actually happen
 
+
+For example:
+
+```ruby
+AddCommentMutation = GraphQL::Relay::Mutation.define do
+  # Used to name derived types:
+  name "AddComment"
+
+  # Accessible from `input` in the resolve function:
+  input_field :postId, !types.ID
+  input_field :authorId, !types.ID
+  input_field :content, !types.String
+
+  # The result has access to these fields,
+  # resolve must return a hash with these keys
+  return_field :post, PostType
+  return_field :comment, CommentType
+
+  # The resolve proc is where you alter the system state.
+  resolve -> (inputs, ctx) {
+    post = Post.find(inputs[:postId])
+    comment = post.comments.create!(author_id: inputs[:authorId], content: inputs[:content])
+
+    {comment: comment, post: post}
+  }
+end
+
+
+```
+
+Under the hood, GraphQL creates:
+  - A field for your schema's `mutation` root
+  - A derived `InputObjectType` for input values
+  - A derived `ObjectType` for return values
+
 The resolve proc:
   - Takes `inputs`, which is a hash whose keys are the ones defined by `input_field`
   - Takes `ctx`, which is the query context you passed with the `context:` keyword
   - Must return a hash with keys matching your defined `return_field`s
 
-Examples:
-  - Definition: [example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L90)
-  - Mount on mutation type: [example](https://github.com/rmosolgo/graphql-relay-ruby/blob/master/spec/support/star_wars_schema.rb#L127)
 
 ## Todo
 
-- Show how to wrap a simple field in a connection field with `ConnectionField.create`
 - Add a `max_page_size` config for connections?
 - Refactor some RelationConnection issues:
   - fix [unbounded count in page info](https://github.com/rmosolgo/graphql-relay-ruby/blob/88b3d94f75a6dd4c8b2604743108db31f66f8dcc/lib/graphql/relay/base_connection.rb#L79-L86), [details](https://github.com/rmosolgo/graphql-relay-ruby/issues/1)
 
 ## More Resources