better performance for exists() method of Query class

[ziaratban]

Q	A
Is bugfix?	yes
New feature?	no
Breaks BC?	no
Tests pass?	yes
Fixed issues	#290

[ziaratban]

@samdark what is milestone for this PR ?

[samdark]

2.1.10. Overall it looks extremely hacky. Need @yiisoft/core-developers and @yiisoft/reviewers opinions about it.

[schmunk42]

Some more explanation why this is better would be nice.
Did you benchmark this?

Also test do not pass.

[samdark]

@schmunk42 the explanation is in #290

[schmunk42]

How about

public function exists($db = null, $optimized = false)

and do the modifications when $optimized is true.

[samdark]

@schmunk42 does it make sense to do it in non-optimized way?

[schmunk42]

@schmunk42 does it make sense to do it in non-optimized way?

I am no mongo expert, my concern is only about BC.

Counterquestion: Why is it not done by mongo, if it makes no difference?

[ziaratban]

@schmunk42 does it make sense to do it in non-optimized way?

@samdark please see Checking if a document exists – MongoDB slow findOne vs find

[samdark]

The link could be added to comment since the code there causes questions immediately.