Added a exists() method which returns boolean whether the result for query exists

[bkvirendra]

This method will return a boolean value, whether the result for the query exists or not.

[rozza]

Hi thanks for the pull request, it can't be merged currently as it needs tests.

[bkvirendra]

I ll add the tests, and send update the pull request! Does that work? @rozza

[MRigal]

exists() could be a nice shortcut, but doing with len() is actually the wrong way of doing it. It is much slower than testing the existence of a result when limiting the queryset to one. And exists() should be faster than len(), like for other DB engines, else it is useless

[jkarni]

And anyhow, in the absence of __nonzero__ the truth-value of the object itself already is len(obj) == 0.
Like MRigal, I also think this could be a useful feature if implemented in a more efficient way. I wouldn't mind submitting a PR for it - would it be welcome?

[rochacbruno]

👍

[emanuelvianna]

👍

[ispmarin]

👍

[rochacbruno]

I also think this could be a useful feature if implemented in a more efficient way. I wouldn't mind submitting a PR for it - would it be welcome?

@jkarni It will be very welcome, can you do it or maybe give some hint?

[jonathansp]

Fix with tests #655
Implements __nonzero__(),__bool__() and has_data()
It does not use __len__ because it will open all documents. If queryset points to 100 documents, 100 queries wil be done. This fix checks only 1 record (1 query) in queryset to return True or False

Use of:

if Person.objects.has_data(): 
    # do something...

is equivalent to

if Person.objects: 
    # do something...

What do you think? @wojcikstefan @rozza ?
Thank you for the tips @wojcikstefan!

[wojcikstefan]

I'd close this PR and handle it in #655 - most of the work is done there already. Anyway, I think @rozza is not a maintainer of this repo anymore, @lig is (right?).

[rozza]

#665 has been merged covering this