[odb-users] [Feature Request] odb::query operator== and operator!=

[Boris Kolpackov]

Hi Markus,

Markus Klemm <markus at markusklemm.net> writes:

> please correct me if I'm wrong, but there seem to be no equality e.g. 
> inequality operator defined for odb::query.

You are correct, these operators are not provided for odb::query.


> This would be very helpful, to for instance, decide if loading of
> data is necessary.

While I can see how this can be useful, implementing these operators
properly will be non-trivial, to say the least. For example, would
you expect these two queries to compare equal?

(query::name == "John" && query::age == 18)
(query::age == 18 && query::name == "John")

What about these two:

!(query::name == "John" || query::name == "Jane")
 (query::name != "John" && query::name != "Jane")

At the same time, it should be pretty easy to keep the data for
your queries in some "canonical" form/order so that it is easy
to decide whether the two queries are equivalent.

Boris