Support pointer in distinct query

[dplewis]

Per #2238 (comment)

Let me know if theres a better way to implement this.

[flovilmart]

@dplewis The mongoObjectToParseObject method should already transform the pointers, perhaps just extract the logic: https://github.com/parse-community/parse-server/blob/master/src/Adapters/Storage/Mongo/MongoTransform.js#L1133

[dplewis]

@flovilmart I extracted the logic because distinct returns a string like 'TestObject$ObjectId' which returns here. https://github.com/parse-community/parse-server/blob/master/src/Adapters/Storage/Mongo/MongoTransform.js#L1024

Edit: I see what you are saying

[flovilmart]

Yeah, I mean what you can do is make a transformPointerString method in the MongoTransform.js module and use it at both places.

[vitaly-t]

I generally do not like this line:

.catch(() => [])

It is dangerous, swallowing all possible errors like that.

Also, I probably would replace this block:

let qs = `SELECT DISTINCT ON ($1:raw) $2:raw FROM $3:name ${wherePattern}`;
if (isArrayField) {
   qs = `SELECT distinct jsonb_array_elements($1:raw) as $2:raw FROM $3:name ${wherePattern}`;
}

with this one:

const transformer = isArrayField ? 'jsonb_array_elements': 'ON';
const qs = `SELECT DISTINCT ${transformer}($1:raw) AS $2:raw FROM $3:name ${wherePattern}`;

[codecov]

Codecov Report

Merging #4471 into master will decrease coverage by 0.12%.
The diff coverage is 92.3%.

@@            Coverage Diff             @@
##           master    #4471      +/-   ##
==========================================
- Coverage   92.98%   92.86%   -0.13%     
==========================================
  Files         118      118              
  Lines        8498     8376     -122     
==========================================
- Hits         7902     7778     -124     
- Misses        596      598       +2

Impacted Files	Coverage Δ
src/Adapters/Storage/Mongo/MongoStorageAdapter.js	96.09% <100%> (-1.66%)	⬇️
src/Adapters/Storage/Mongo/MongoTransform.js	85.4% <83.33%> (+0.04%)	⬆️
...dapters/Storage/Postgres/PostgresStorageAdapter.js	97.07% <91.66%> (-0.09%)	⬇️
src/Adapters/Files/GridStoreAdapter.js	100% <0%> (ø)	⬆️
src/RestWrite.js	93.46% <0%> (ø)	⬆️
src/Adapters/Auth/meetup.js	89.47% <0%> (+5.26%)	⬆️

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[dplewis]

[vitaly-t]

Can't see which PR made this one out-of-date, but requested a branch update, since it is required.

[dplewis]

There were node packages that were merged

[vitaly-t]

LGTM.

[srameshr]

@dplewis Does not work for me.

const query = new Parse.Query('MyClass');
query.include('content');
query.distinct('content.objectId');
query.find();

It just returns records with duplicate content column.

[flovilmart]

Well, the single unit test that is exactly what you describe passes. So open a an issue with the full details as well as code examples and relevant logs

[dplewis]

Do your objects have a field called “content.objectId”? Make sure you are querying the right field. Please open an issue with examples and I’ll look it over

[srameshr]

content is a pointer field on MyClass. I need to fetch records with unique content pointer field. I just this approach, like fieldName.objectId in some other thread

[flovilmart]

well @srameshr did you read the test file here

because what you're doing isn't how it's supposed to be used.

[srameshr]

@flovilmart query.distinct('pointer') assuming pointer is the field name, so for me, the query would be query.distinct('content'), cos content is my field name. Even this did not work and also am I missing something?

[flovilmart]

did you notice that in the test it is:

const query = new Parse.Query(TestObject);
query.distinct('pointer').then((results) => {

});

and in your example:

const query = new Parse.Query('MyClass');
query.include('content');
query.distinct('content.objectId');
query.find();

Well if you don't see the differences now, I'm not sure how to help you.

[srameshr]

Shit, ok got it. .distinct returns a promise with distinct values. My bad.

[flovilmart]

Well, that's what's written in the test file. Next time consider reading what the maintainers share as well as perhpas the docs: https://docs.parseplatform.org/js/guide/#distinct

[srameshr]

I heard you the first time.