Merge pull request #5 from hoverinc/readme-update

Update README.md

Author: glytch

README.md

@@ -1,7 +1,9 @@
 # Graphql::EagerLoad
 
-This gem traverses your graphql query looking for fields on types that match
-associations on those types. For each field found to be an association, this
+This gem assumes you are using [Rails](http://rubyonrails.org) and [ActiveRecord](https://guides.rubyonrails.org/active_record_querying.html). And that your GraphQL types and fields map as closely to your data model as possible. It uses those assumptions, or conventions, to handle a N+1 prevention for you.
+
+It does so by traversing your graphql query looking for fields on types that match
+associations on those types' corresponding models. For each field found to be an association, this
 gem adds those associations to an [ActiveRecord::QueryMethods#includes](https://api.rubyonrails.org/classes/ActiveRecord/QueryMethods.html#method-i-includes) hash. That hash can then be used to
 eager load the associations of records returned in your graphql resolver.
 
@@ -35,6 +37,43 @@ end
 
 The `.eager_load_model` and `#associations_to_eager_load` methods are provided by this gem.
 
+
+If your type defines a custom method for a field that maps to an ActiveRecord association, this gem will ignore that association and let your method handle it. If you still want to eager load the association in that case you need to let the gem know.
+
+```ruby
+module Types
+  class User < Types::Base
+    field :estimates, [Types::Estimate], null: false
+    field :profile_photo, Types::File, null: true
+    
+    def profile_photo
+      object.profile_photo if object.profile_photo.attached?
+    end
+    
+    def self.allow_include_builder_fields
+      [:profile_photo]
+    end
+  end
+end
+```
+
+Given this query: 
+
+```javascript
+users {
+  id
+  estimates {
+    id
+  }
+  profilePhoto {
+    redirectUrl
+    filename
+  }
+}
+```
+
+The output of the `#associations_to_eager_load` helper method would be `{estimates: {}, profile_photo: {blob: {}}`. Without the `.allow_include_builder_fields` class method the output would be `{estimates: {}}`.
+
 ## Development
 
 After checking out the repo, run `bundle` to install dependencies. Then, run `bundle exec rake spec` to run the tests. You can also run `bundle exec bin/console` for an interactive prompt that will allow you to experiment.