Add synchronous version of persistCache

[andrewshirk]

This PR is intended to provide a simple, non-breaking way to start persisting a cache by first restoring the cache synchronously, for apps with small localStorage requirements. This is just a proposal at this point.

[apollo-cla]

@andrewshirk: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[codecov-io]

Codecov Report

Merging #299 into master will increase coverage by 2.15%.
The diff coverage is 92%.

@@            Coverage Diff             @@
##           master     #299      +/-   ##
==========================================
+ Coverage   72.95%   75.11%   +2.15%     
==========================================
  Files          10       11       +1     
  Lines         196      221      +25     
  Branches       30       33       +3     
==========================================
+ Hits          143      166      +23     
- Misses         50       52       +2     
  Partials        3        3

Impacted Files	Coverage Δ
src/index.ts	100% <100%> (ø)	⬆️
src/persistCacheSync.ts	91.66% <91.66%> (ø)

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[wtrocki]

Awesome change! Thank you so much for controbution. We are missing following items to get it merged:

• Readme.md chapter on sync api
• Unit test - if can be simply copy paste with changed classes
• exporting file to package level so it can be used

Once again thank you so much for this awesome contribution.

PS: I'm traveling for the rest of the week so I will be able to merge it on next monday after testing it and release the change.

[wtrocki]

Some minor changes suggested.

[wtrocki]

Awesome work. I will sit down next week and make sure that this is merged and new version of package is released.

[andrewshirk]

Thanks for your support on this!

[wtrocki]

Reviewing!

[wtrocki]

@andrewshirk I see that unit tests are not passing. I see some issues when playing with them locally. Are you still working on this? I do not want to duplicate work.
Apart from that, this is an solid merge - I would also get that released by official channel and promote this change on twitter.

[andrewshirk]

@wtrocki I haven't done any more work on it yet. I ran out of time last week, but will probably have some tonight. Just let me know what'd you like. Thanks again!

[wtrocki]

Generally I see that tests using simulateApp that still uses async. Generally I would simply write separate unit tests that tests only restore. This should not be hard and it will test all code that we have added. Repeating all tests for the sync api makes no sense - we just want to check addition we have made. I would just remove current tests and write simple one that will just test async api.
There is no need for mocks as well.

Thank you so much for contribution.

[andrewshirk]

@wtrocki Great, thanks for the clarification. You suggested copy/pasting earlier, so wasn't sure about that. I will get to it ASAP.

[wtrocki]

It was my mistake for not being clear. I should have said to copy paste only the restore test and ignore the rest.

[wtrocki]

Very simple test that works for me:

import { InMemoryCache } from 'apollo-cache-inmemory';
import { persistCacheSync, SynchronousCachePersistor } from '../';
import MockStorage from '../__mocks__/MockStorage';
import { ApolloLink } from 'apollo-link';
import Observable = require('zen-observable');
import ApolloClient from 'apollo-client';
import gql from 'graphql-tag';

jest.useFakeTimers();
describe('persistCacheSync', () => {
  describe('setup', () => {
    it('persist cache', async () => {
      const operation = gql`
      {
        hello
      }
    `;
    const result = { data: { hello: 'world' } };
      const storage = new MockStorage();
      const cache = new InMemoryCache();

      const cachePersistor = new SynchronousCachePersistor({ cache, storage });

      const link = new ApolloLink(() => Observable.of(result));
      const client = new ApolloClient({ cache, link });
      expect(cache.extract()).toEqual({});

      await client.query({ query: operation });
      jest.runTimersToTime(
        persistOptions.debounce ? persistOptions.debounce + 1 : 1001
      );

      const cache2 = new InMemoryCache();
      const cachePersistor2 = new SynchronousCachePersistor({ cache: cache2, storage });
      cachePersistor2.restoreSync();
      const keys = Object.keys(cache2.extract());
      expect(keys.length).toEqual(2);
    });
  });
});

[wtrocki]

Sadly I cannot push changes to your branch, but I have also needed to change:
export * from './persistCacheSync'; in index.ts
and exported every sync version (users will not be able to use it without exporting them)

[andrewshirk]

Wonderful. I'll have time to work on this tonight.

[andrewshirk]

@wtrocki I'll investigate the test failures.

[andrewshirk]

MockStorage is an async API, so we need a MockStorageSync I suppose.

[andrewshirk]

@wtrocki I gave you push access to my repo, if you want to make any final tweaks.

[wtrocki]

Awesome work. I will play with it in sample app and merge changes. Thank you so much

[wtrocki]

@andrewshirk Amazing collaboration and great work on the feature. I have spent some time playing with the new API. Merging the change and doing a new release of dev package.

[andrewshirk]

@wtrocki Super! Thanks again for all your help and support!