Add "hidden" property attribute

[gramian]

What does this PR do?

This new boolean property attribute called hidden excludes properties from a projection containing a * (star).

Motivation

ZetaSQL

Related issues

#1439

Additional Notes

This is the interesting change set: https://github.com/ArcadeData/arcadedb/pull/1503/files#diff-1ebfff8995bc54eab127a05a7f09d799b215972c6aa872635f37d86e824fb0b3

• Basically now the any projection with a * (isAll) gets parsed property by property not by copy any more.
• SELECT * FROM x works, but SELECT FROM x does not.
  • @lvca I cannot figure out why this is not working.

Checklist

• I have run the build using mvn clean package command
• My unit tests cover both failure and success scenarios

[robfrank]

@gramian I added the missing part, essentially I updated the sql grammar and added some tests.

So, how it works?

If a property is configure to be hidden, when using the

SELECT * FROM TypeWithHiddenPropery

than the hidden property isn't present in the result set.

But, when not using the *:

SELECT  FROM TypeWithHiddenPropery

than the hidden property IS present in the result set.

After a fast call with @lvca, we think this is the right way to implement the feature. When a the query is written without a projection, the * in this case, it means the the query should fetch the whole content, hidded properties included.

WDYT?

[gramian]

Hmm, OK.

I always thought of SELECT FROM as short form of SELECT * FROM. Are there other differences between these two forms? Performance-wise for example?

[robfrank]

They are working differently in the parser. The * generates a projection that is then interpreted as "all" , while the "blank" doesn't generate any projection.
On performace side, I think it depends more on the whole query structure rather than a single part of the statement.

If you think the feature is valuable in this incarnation, we can merge it :)

[gramian]

It definitely is.

I am thinking about documentation for users, so when to use which and why. So given a large document, meaning many properties, SELECT FROM would be slightly faster as just the entire document is returned, right? And this ties now in with hidden; because the whole doc is returned the hidden properties are included, whereas using SELECT * FROM computes a projection in which hidden is applied. What else needs to be stated in this regard?

The point being hidden is aimed only at projections.

[robfrank]

exactly: you get to the point.

[lvca]

Exactly. SELECT FROM returns the whole record, instead * returns all the properties for the record. The result overlaps most of the times, but with the new hidden feature I think select from should still return the hidden properties, because you're asking the object itself.