From 644fd3efef9d30e2616969f8dbf00d9d2fecf91e Mon Sep 17 00:00:00 2001
From: Kushal Pandya <kushalspandya@gmail.com>
Date: Tue, 11 Jun 2019 16:28:01 +0530
Subject: Add `fragmentMatcher` support in cacheConfig

---
 app/assets/javascripts/lib/graphql.js | 40 ++++++++++++++++++++++++++++++++++-
 1 file changed, 39 insertions(+), 1 deletion(-)

diff --git a/app/assets/javascripts/lib/graphql.js b/app/assets/javascripts/lib/graphql.js
index 5857f9e22ae..ab8bae60ac2 100644
--- a/app/assets/javascripts/lib/graphql.js
+++ b/app/assets/javascripts/lib/graphql.js
@@ -1,5 +1,5 @@
 import { ApolloClient } from 'apollo-client';
-import { InMemoryCache } from 'apollo-cache-inmemory';
+import { InMemoryCache, IntrospectionFragmentMatcher } from 'apollo-cache-inmemory';
 import { createUploadLink } from 'apollo-upload-client';
 import { ApolloLink } from 'apollo-link';
 import { BatchHttpLink } from 'apollo-link-batch-http';
@@ -7,12 +7,50 @@ import csrf from '~/lib/utils/csrf';
 
 export default (resolvers = {}, config = {}) => {
   let uri = `${gon.relative_url_root}/api/graphql`;
+  const { introspectionQueryResultData, cacheConfig } = config;
 
   if (config.baseUrl) {
     // Prepend baseUrl and ensure that `///` are replaced with `/`
     uri = `${config.baseUrl}${uri}`.replace(/\/{3,}/g, '/');
   }
 
+  if (introspectionQueryResultData) {
+    // eslint-disable-next-line no-param-reassign
+    config.cacheConfig = cacheConfig || {};
+
+    // Extract typenames from provided introspection Query data.
+    // eslint-disable-next-line no-underscore-dangle
+    const typeNames = introspectionQueryResultData.__schema.types
+      .map(type => type.possibleTypes)
+      .reduce((acc, item) => acc.concat(item), [])
+      .map(item => item.name);
+
+    Object.assign(config.cacheConfig, {
+      fragmentMatcher: new IntrospectionFragmentMatcher({
+        introspectionQueryResultData,
+      }),
+      dataIdFromObject: obj => {
+        // We need to create a dynamic ID for each entry and
+        // each entry can have the same ID as the ID in a commit ID,
+        // So we create a unique cache ID with the path and the ID.
+        // eslint-disable-next-line no-underscore-dangle
+        if (typeNames.indexOf(obj.__typename) > -1) {
+          return `${obj.flatPath}-${obj.id}`;
+        }
+
+        // If the type doesn't match any of the above we
+        // fallback to using the default Apollo ID.
+        // eslint-disable-next-line no-underscore-dangle
+        return obj.id || obj._id;
+      },
+
+      // Override addTypename to force it to be
+      // `true` to ensure that fragmentMatcher
+      // always has `__typename` available.
+      addTypename: true,
+    });
+  }
+
   const httpOptions = {
     uri,
     headers: {
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