Add support to Relay style pagination (#4)

GraphQL-query-resolver will now follow any relay style pagination queries down to edges and nodes, so we can preload queries that are wrapped in relay queries.

Sample relay query:

```graphql
    query {
        vendors(first: 5) {
          edges {
            node {
              id
              name
              ingredients {
                name
                quantity
              }
            }
            cursor
          }
          pageInfo {
            endCursor
            hasNextPage
            hasPreviousPage
            startCursor
          }
        }
      }
```

Author: nettofarah

.gitignore

@@ -8,3 +8,4 @@
 /spec/reports/
 /tmp/
 .byebug_history
+.idea

lib/graphql/query_resolver.rb

@@ -22,20 +22,41 @@ def self.run(model_class, context, return_type)
       to_load
     end
 
-    def self.map_dependencies(class_name, ast_node)
-      dependencies = {}
+    def self.using_relay_pagination?(selection)
+      selection.name == 'edges'
+    end
+
+    def self.map_relay_pagination_depencies(class_name, selection, dependencies)
+      node_selection = selection.selections.find { |sel| sel.name == 'node' }
+
+      if node_selection.present?
+        map_dependencies(class_name, node_selection, dependencies)
+      else
+        dependencies
+      end
+    end
+
+    def self.has_reflection_with_name?(class_name, selection_name)
+      class_name.reflections.with_indifferent_access[selection_name].present?
+    end
+
+    def self.map_dependencies(class_name, ast_node, dependencies={})
       ast_node.selections.each do |selection|
         name = selection.name
 
-        if class_name.reflections.with_indifferent_access[selection.name].present?
+        if using_relay_pagination?(selection)
+          map_relay_pagination_depencies(class_name, selection, dependencies)
+          next
+        end
+
+        if has_reflection_with_name?(class_name, name)
           begin
             current_class_name = selection.name.singularize.classify.constantize
             dependencies[name] = map_dependencies(current_class_name, selection)
           rescue NameError
             selection_name = class_name.reflections.with_indifferent_access[selection.name].options[:class_name]
             current_class_name = selection_name.singularize.classify.constantize
             dependencies[selection.name.to_sym] = map_dependencies(current_class_name, selection)
-
             next
           end
         end

spec/graphql/query_resolver_spec.rb

@@ -98,4 +98,32 @@
 
     expect(queries.size).to eq(2)
   end
+
+  it 'works with pagination' do
+    query = %{
+      query {
+        vendors(first: 5) {
+          edges {
+            node {
+              id
+              name
+              ingredients {
+                name
+                quantity
+              }
+            }
+            cursor
+          }
+          pageInfo {
+            hasNextPage
+          }
+        }
+      }
+    }
+    queries = track_queries do
+      GQL.query(query)
+    end
+
+    expect(queries.size).to eq(2)
+  end
 end

spec/support/graphql_schema.rb

@@ -60,6 +60,14 @@
 
   field :id, types.ID
   field :name, types.String
+
+  field :ingredients do
+    type types[IngredientType]
+
+    resolve -> (obj, args, ctx) {
+      obj.ingredients
+    }
+  end
 end
 
 IngredientType = GraphQL::ObjectType.define do
@@ -97,6 +105,14 @@
       end
     }
   end
+
+  connection :vendors, VendorType.connection_type, max_page_size: 50 do
+    resolve -> (obj, args, ctx) {
+      GraphQL::QueryResolver::run(Vendor, ctx, VendorType) do
+        Vendor.all.to_a
+      end
+    }
+  end
 end
 
 Schema = GraphQL::Schema.define do