optional value returned by mongocxx::collection member functions

[li ning]

The insert, delete return an optional, but doc has not talk about in what situation the return value is null. I mean

auto r = connection.delete_one({x})

what is the different between:

if(r) and if(r->deleted_count() == 1)

If I need to check the delete result, which statement should I use?

In what situation the return value r will be NULL? I mean optional operator bool() const  return false

[li ning]

I check source code find some method will return null like find_one, but other(delete_one) will not return null. This is inconsistent.

For methods return a result_type like insert delete, there is no need wrap the result_type by optional, because the result_type already can take the semantic of "no value", warp it by a optional means want to express "no value of no value", that is meaningless.

This design confuse me (so I ask this question), in fact only methods which return an "concrete type"(like find) needs wrap by optional to represent "no value"

在 2016年4月7日星期四 UTC+8下午6:41:34，li ning写道：

[Andrew Morrow]

Hi -

The intention of the methods that return an optional<T> where T is in the mongocxx::result namespace is that they may or may not return a T value. The case where they do not return a T value is (intended) to represent things like unacknowledged operations (e.g. a w:0 write).

However, at this time, the C++11 driver does not ever return a disengaged optional in these circumstances, because of an issue in the C driver.

I've filed https://jira.mongodb.org/browse/CXX-894 so that we can resolve this when the underlying issue in the C driver is resolved.

Thanks,

Andrew

On Thu, Apr 7, 2016 at 9:45 PM, li ning <li.ni...@gmail.com> wrote:

I check source code find some method will return null like find_one, but other(delete_one) will not return null. This is inconsistent.

For methods return a result_type like insert delete, there is no need wrap the result_type by optional, because the result_type already can take the semantic of "no value", warp it by a optional means want to express "no value of no value", that is meaningless.

This design confuse me (so I ask this question), in fact only methods which return an "concrete type"(like find) needs wrap by optional to represent "no value"

在 2016年4月7日星期四 UTC+8下午6:41:34，li ning写道：

The insert, delete return an optional, but doc has not talk about in what situation the return value is null. I mean

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