$not operator

[maheshrajamani]

What this PR does:

Which issue(s) this PR fixes:
Fixes #

Checklist

• Changes manually tested
• Automated Tests added/updated
• Documentation added/updated
• CLA Signed: DataStax CLA

[tatu-at-datastax]

If this is done to flip between 1 and -1, more efficient way would be to use BigDecimal.negate() (https://docs.oracle.com/javase/8/docs/api/java/math/BigDecimal.html#negate-- )

But I guess I am not sure what the logic here really is? Negative values can't match anything, I guess that is the idea?

EDIT: this ^^^ makes sense when at later point negative value is converted to "$size NOT equals X"

[tatu-at-datastax]

LGTM: added some questions, but nothing blocking merge.

[tatu-at-datastax]

LGTM

[vkarpov15]

I'm curious about why $not is an array. In MongoDB, $not is an object like the following:

find({
  num: {
    $not: {
      $lt: 42
    }
  }
}); // Equivalent to `find({ num: { $gte: 42 } })`

Is there a reason for making $not an array?

[maheshrajamani]

I'm curious about why $not is an array. In MongoDB, $not is an object like the following:

I made it in line with $and and $or operator. It does and of conditions below it. Do we have to change this?

[tatu-at-datastax]

I'm curious about why $not is an array. In MongoDB, $not is an object like the following:

I made it in line with $and and $or operator. It does and of conditions below it. Do we have to change this?

Hmmmh. Good point, thank you for pointing it out. It is interesting Mongo has this discrepancy: $and and $or take Array, $not for some reason Object. Go figure.

Earlier we wanted to be highly Mongo-compatible, and I would have suggested we follow its lead.
But now we are moving away from that.
Still, we are mostly extending things and not changing handling of features Mongo has.
So I am not 100% sure which way we should go.

I think we need to discuss this on our daily meeting @maheshrajamani see what Aaron thinks.

[tatu-at-datastax]

Based on discussion with @amorton, I think the preferred option is to use JSON Object, same as how Mongo behaves.
I guess it also makes sense logically, come to think of it: not is typically unary operation whereas and and or are binary. So taking in Array would be more likely implicit "not and" (and possibly more confusing).

[vkarpov15]

Another reason why we should make $not a unary operator is that Mongoose's filter casting logic assumes $not is unary. In the following script, Mongoose throws a CastError CastError: Cast to number failed for value "[ { '$gt': 42 } ]" (type Array) at path "age" for model "Test":

'use strict';

const mongoose = require('mongoose');

mongoose.set('debug', true);

run().catch(err => console.log(err));

async function run() {
  await mongoose.connect('mongodb://127.0.0.1:27017/mongoose_test');

  const schema = new mongoose.Schema({ age: Number });
  const Test = mongoose.model('Test', schema);

  await Test.find({ age: { $not: [{ $gt: 42 }] } });
  console.log('Done');
}

However, await Test.find({ age: { $not: { $gt: 42 } } }); (object rather than array for $not) casts correctly. So if we want to be compatible with what Mongoose expects, then $not should be unary.

[maheshrajamani]

@vkarpov15 @tatu-at-datastax Have made the $not to accept one object as value. If you want to do another review of it.

[vkarpov15]

Nice, I'm glad you tested this. I checked whether multiple $not works in MongoDB and Mongoose: MongoDB supports it, but Mongoose doesn't. Something for Mongoose to fix.