feat(cacheMiddleware): add clearOnMutation option (thanks @haruska)

* update cache to optionally clear on mutation

* add option to readme

README.md

@@ -71,6 +71,7 @@ Middlewares
   - `onInit` - function(cache) which will be called once when cache is created. As first argument you receive `QueryResponseCache` instance from `relay-runtime`.
   - `allowMutations` - allow to cache Mutation requests (default: `false`)
   - `allowFormData` - allow to cache FormData requests (default: `false`)
+  - `clearOnMutation` - clear the cache on any Mutation (default: `false`)
 - **authMiddleware** - for adding auth token, and refreshing it if gets 401 response from server.
   - `token` - string which returns token. Can be function(req) or Promise. If function is provided, then it will be called for every request (so you may change tokens on fly).
   - `tokenRefreshPromise`: - function(req, res) which must return promise or regular value with a new token. This function is called when server returns 401 status code. After receiving a new token, middleware re-run query to the server seamlessly for Relay.

src/middlewares/cache.js

@@ -10,10 +10,11 @@ type CacheMiddlewareOpts = {|
   onInit?: (cache: QueryResponseCache) => any,
   allowMutations?: boolean,
   allowFormData?: boolean,
+  clearOnMutation?: boolean,
 |};
 
 export default function queryMiddleware(opts?: CacheMiddlewareOpts): Middleware {
-  const { size, ttl, onInit, allowMutations, allowFormData } = opts || {};
+  const { size, ttl, onInit, allowMutations, allowFormData, clearOnMutation } = opts || {};
   const cache = new QueryResponseCache({
     size: size || 100, // 100 requests
     ttl: ttl || 15 * 60 * 1000, // 15 minutes
@@ -24,8 +25,13 @@ export default function queryMiddleware(opts?: CacheMiddlewareOpts): Middleware
   }
 
   return next => async req => {
-    if (req.isMutation() && !allowMutations) {
-      return next(req);
+    if (req.isMutation()) {
+      if (clearOnMutation) {
+        cache.clear();
+      }
+      if (!allowMutations) {
+        return next(req);
+      }
     }
 
     if (req.isFormData() && !allowFormData) {