I'm really not happy to see that proto3 removed the ability in generate
code for check whether a field exits or not.
For a message like this:
message Test1 {
required int32 a = 1;
}
If field a is present, the encoded message will have field with id 1 and
its value. If the field is not set, the encoded message will not have field
id 1.
In proto2 generated code, it provides a has method to check whether the
field exists or not.
In proto3, this is no such thing. During deserialization, if the field is
not exists, default value is set. So you can't tell whether the field does
not exist or have a default value. That doesn't match the underline
encoding anymore.
This is a breaking change and will portentially impact a lot of people.
Basically we're losing nullable support.
For our project, we heavily depends on that. There are workarounds (add
a Boolean field) but it is ugly. I think that will stop us from moving from
proto2 to proto3 (may need find alternatives).
Can we add the functionality back?
On Saturday, March 26, 2016 at 11:47:08 AM UTC-7, Ilia Mirkin wrote:
> Use proto2, which has the has_* checks per field. (Using get_* you
> still get the default value, of course.) It's extremely unfortunate
> that this functionality was removed in proto3, I see that making
> proto3 unattractive for all but the simplest uses of protos. I know in
> almost every protobuf use-case I've had, the presence accessors were
> imperative to proper operation.
>
> On Sat, Mar 26, 2016 at 2:43 PM, Yoav H <joe.dai...@gmail.com
> <javascript:>> wrote:
> > Hi,
> >
> > I wanted ask regarding the decision to populate fields with default
> values,
> > even if they do not appear in the encoded message.
> > If I want to send a "patch" message, where I want to update just the
> > provided fields, how can I do that with protobuf (without adding
> IsXXXSet
> > for every field)?
> >
> > Why not add another type, representing a default value?
> > So the schematics would be, if the field is missing, it is null, and if
> the
> > field exists, but with this "missing value" type, it will get the
> default
> > value?
> >
> > Thanks,
> > Yoav.
> >
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