Support fragments with aliases for CacheKeyBuilder (#25)

Author: DmitryTsepelev

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## master
 
+- [PR#25](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/pull/25) Support fragments with aliases for CacheKeyBuilder ([@DmitryTsepelev][])
+
 ## 1.0.0 (2020-06-13)
 
 - [PR#24](https://github.com/DmitryTsepelev/graphql-ruby-fragment_cache/pull/24) Add nil caching. **BREAKING CHANGE**: custom cache stores must also implement `#exist?(key)` method ([@DmitryTsepelev][])

lib/graphql/fragment_cache/cache_key_builder.rb

@@ -76,7 +76,13 @@ def alias_selections
 
         def lookup_alias_node(nodes, name)
           return if nodes.empty?
+
           nodes.find do |node|
+            if node.is_a?(GraphQL::Language::Nodes::FragmentSpread)
+              node = @query.fragments[node.name]
+              raise("Invariant: Can't look ahead to nonexistent fragment #{node.name} (found: #{@query.fragments.keys})") unless node
+            end
+
             return node if node.alias?(name)
             child = lookup_alias_node(node.children, name)
             return child if child

spec/graphql/fragment_cache/cache_key_builder_spec.rb

@@ -221,4 +221,48 @@
 
     specify { is_expected.to eq "schema_key/posts/0/cachedTitle[]" }
   end
+
+  context "when query has fragment" do
+    let(:query) do
+      <<~GQL
+        fragment PostFragment on PostType {
+          id
+          author: cachedAuthor {
+            name
+          }
+        }
+
+        query getPost($id: ID!) {
+          post(id: $id) {
+            ...PostFragment
+          }
+        }
+      GQL
+    end
+
+    let(:path) { ["post", "author"] }
+
+    specify { is_expected.to eq "schema_key/post(id:1)/cachedAuthor[name]" }
+  end
+
+  context "when query has inline fragment" do
+    let(:query) do
+      <<~GQL
+        query getPost($id: ID!) {
+          post(id: $id) {
+            ...on PostType {
+              id
+              author: cachedAuthor {
+                name
+              }
+            }
+          }
+        }
+      GQL
+    end
+
+    let(:path) { ["post", "author"] }
+
+    specify { is_expected.to eq "schema_key/post(id:1)/cachedAuthor[name]" }
+  end
 end

spec/graphql/fragment_cache/object_helpers_spec.rb

@@ -180,6 +180,94 @@
         })
       end
 
+      context "when query has fragment" do
+        let(:author) { User.new(id: 1, name: "John") }
+        let!(:post) { Post.create(id: 1, title: "object test", author: author) }
+
+        let(:query_with_fragment) do
+          <<~GQL
+            fragment PostFragment on PostType {
+              id
+              author: cachedAuthor {
+                name
+              }
+            }
+
+            query getPost($id: ID!) {
+              post(id: $id) {
+                ...PostFragment
+              }
+            }
+          GQL
+        end
+
+        let(:resolver) do
+          ->(id:) do
+            Post.find(id)
+          end
+        end
+
+        it "returns cached fragment" do
+          author_data = execute_query(query_with_fragment).dig("data", "post", "author")
+          expect(author_data).to eq({"name" => author.name})
+        end
+
+        context "when fragment name is wrong" do
+          let(:query_with_fragment) do
+            <<~GQL
+              fragment PostFragment on PostType {
+                id
+                author: cachedAuthor {
+                  name
+                }
+              }
+
+              query getPost($id: ID!) {
+                post(id: $id) {
+                  ...WrongPostFragment
+                }
+              }
+            GQL
+          end
+
+          it "returns cached fragment" do
+            error_message = execute_query(query_with_fragment).dig("errors").first["message"]
+            expect(error_message).to eq("Fragment WrongPostFragment was used, but not defined")
+          end
+        end
+      end
+
+      context "when query has inline fragment" do
+        let(:author) { User.new(id: 1, name: "John") }
+        let!(:post) { Post.create(id: 1, title: "object test", author: author) }
+
+        let(:query_with_fragment) do
+          <<~GQL
+            query getPost($id: ID!) {
+              post(id: $id) {
+                ...on PostType {
+                  id
+                  author: cachedAuthor {
+                    name
+                  }
+                }
+              }
+            }
+          GQL
+        end
+
+        let(:resolver) do
+          ->(id:) do
+            Post.find(id)
+          end
+        end
+
+        it "returns cached fragment" do
+          author_data = execute_query(query_with_fragment).dig("data", "post", "author")
+          expect(author_data).to eq({"name" => author.name})
+        end
+      end
+
       context "with multiple aliases" do
         let(:query) do
           <<~GQL