Eliminate cache.writeData.

[benjamn]

In PR #5909, I referred to cache.writeData as a "foot-seeking missile" because it's one of the easiest ways to turn your faulty assumptions about how the cache represents data internally into cache inconsistency and corruption.

PR #5909 introduced an alternative api, cache.modify(id, modifiers), which aims to take the place of the more "surgical" uses of cache.writeData. Somewhat to my surprise, in almost every case where cache.writeData was used in our tests, an appropriate query was already sitting very close by, making cache.writeQuery just as easy to call.

If you think your life is worse now that you have to pass a query to cache.writeQuery or a fragment to cache.writeFragment, please realize that cache.writeData was dynamically creating a fresh query or fragment behind the scenes, every time it was called, so it was actually doing a lot more work than the equivalent call to cache.writeQuery or cache.writeFragment.

Left to do:

• Update the relevant documentation to stop recommending cache.writeData.
• Put a note in CHANGELOG.md.
• Show an example of moving from cache.writeData to cache.writeQuery in the Migration Guide.

[hwillson]

🎉 @benjamn! The code changes look awesome as usual. I added one small Migration Guide mention in the TODO list.

[bwhitty]

Huh, stumbling upon this is exciting. We're doing a deep integration into client-side cache management and local state/resolvers and it was never truly clear to me why all the different cache modification APIs existed.

[codecov]

Codecov Report

Merging #5923 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5923      +/-   ##
==========================================
- Coverage   95.24%   95.20%   -0.04%     
==========================================
  Files          89       88       -1     
  Lines        3703     3674      -29     
  Branches      909      903       -6     
==========================================
- Hits         3527     3498      -29     
  Misses        154      154              
  Partials       22       22              

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[hwillson]

We should be all set here @benjamn. I have several more local state section changes coming, but since they aren't specifically related to writeData, I'll get them into separate PR's. Thanks!

[stubailo]

Neat!

[duskmoon314]

I was following the doc about local state management which still includes client.writeData. I think this is a small mistake and needs to be solved.

[drewkht]

@duskmoon314 They have updated documentation for these changes in the v3.0 beta branch.

[AndreiRailean]

this document still talks about cache.writeData https://www.apollographql.com/docs/tutorial/local-state

[hwillson]

Thanks @AndreiRailean - we're working on changes to the tutorial to address this.

[nisarhassan12]

Thanks, @hwillson this is my first time with the apollo-client was following the tutorial https://www.apollographql.com/docs/tutorial/local-state to learn it which uses cache.writeData.

I was not able to figure out why it's not working.

I'm looking forward to the update in the tutorial. Thanks.

[idkjs]

Are there docs on the cache.modify() change anywhere? Thank you.

[idkjs]

@duskmoon314 They have updated documentation for these changes in the v3.0 beta branch.

Link is dead.
https://www.apollographql.com/docs/react/caching/cache-interaction/#gatsby-focus-wrapper
https://www.apollographql.com/docs/react/api/cache/InMemoryCache/#modifier-functions