feat(ParseObject): enable subclasses to set initial values for props

[RaschidJFR]

Sobclasses of ParseObject where unable to set initial values for their props and maintain them after fetching from the server. The function ParseObject.fromJSON() has been modified to allow this feature. Two test cases have been added.

It may close parse-community/parse-server#5521

[codecov]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 92.38%. Comparing base (5a6682b) to head (9b5c177).
Report is 896 commits behind head on alpha.

Files with missing lines	Patch %	Lines
src/ParseObject.js	88.88%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            alpha     #924      +/-   ##
==========================================
+ Coverage   92.34%   92.38%   +0.03%     
==========================================
  Files          54       54              
  Lines        5294     5302       +8     
  Branches     1191     1194       +3     
==========================================
+ Hits         4889     4898       +9     
+ Misses        405      404       -1     

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[dplewis]

const o = constructor ? new constructor(json) : new ParseObject(json.className) should be fine for your test to work.

There are other issues this brings up. There are other Subclasses of ParseObject like _User and _Session that will try to set readonly fields. You could try to clone the json and delete the readonly fields before passing to the constructor but I don't know what other issue this would cause.

[dplewis]

@RaschidJFR Thoughts?

[RaschidJFR]

Yes, sorry I didn’t reply earlier. I’ve already done that with good results. Haven’t pushed though.

I’ve got almost all tests passing now, just a couple left. What I’m trying to figure out now is a way to prevent pending ops from overwriting the properties set in the constructor.

Tomorrow I’ll push my progress so anyone can have a look.

[RaschidJFR]

@dplewis So I pushed my last commit... it turns out that it was just what you suggested. I havn't continued working on it since a couple of weeks so I can't remember exactly where I am, I'll retake it hopefully soon.

For now there are only a couple of tests failing for ParseObject: 'conver from JSON' and `retrieve subclass objects' (seems like we're back to square one). I just need to figure out how to keep the attributes from _finishFetch() over the PendingOps.

[victorx98]

@RaschidJFR @dplewis Any update on this PR? Are we going to merge it anytime soon? Thanks!

[RaschidJFR]

Hi @victorx98 Sorry, work is keeping me busy so I won't be able to re-take it at least for the next 4 weeks. I see there's been increasing activity around this topic lately so I will dive into it when I'm out of homework. Meanwhile anyone how wishes to retake the subject is welcome to give a hand.

[dplewis]

Closing as this feature already exists. You can override the initialize function.

const Subclass = Parse.Object.extend('Subclass', {
 initialize(_attributes, _options, number) {
   this.number = number || -1;
 },
});
const object = new Subclass({}, {}, 57);
object.number // 57

[mtrezza]

@dplewis That looks interesting, have we documented this use of Parse.Object.extend anywhere?

[dplewis]

https://parseplatform.org/Parse-SDK-JS/api/6.0.0/Parse.Object.html#.extend

Should probably remove the docs for Backbone compatibility