Way to figure out the fields that are modified

[Ananth Arockia]

Hello,

I am exploring protobuf to use it in my project.

I would like to have a message defined in a .proto file. All the
fields in this message would be "optional" due to the fact that the
message producer in my project context would set just a subset of
fields. Can someone please clarify

1. Is there a way to figure out just the fields that are being set in
the message? I would require this after my message is deserialized.
2. does field_count() always return the total number of fields defined
in the message in .proto?
3. Is Reflection the only option to set fields directly/indirectly via
field numbers?

Thanks, Ananth

[Jason Hsueh]

On Mon, Jun 21, 2010 at 8:23 AM, Ananth Arockia <ananth....@gmail.com> wrote:

Hello,

I am exploring protobuf to use it in my project.

I would like to have a message defined in a .proto file. All the
fields in this message would be "optional" due to the fact that the
message producer in my project context would set just a subset of
fields. Can someone please clarify

1. Is there a way to figure out just the fields that are being set in
the message? I would require this after my message is deserialized.

You can check the has() bits (see the tutorial: http://code.google.com/apis/protocolbuffers/docs/tutorials.html) Alternatively, you can define your protocol such that if the field is set, it is not equal to the default value. Then instead of testing has_foo(), you could test foo() != 0 (or whatever the default is).

 

2. does field_count() always return the total number of fields defined
in the message in .proto?

Assuming you mean Descriptor::field_count(), yes.

 

3. Is Reflection the only option to set fields directly/indirectly via
field numbers?

You could also generate the serialized format by hand and then merge that into your message...but Reflection is friendlier :-)

Thanks, Ananth

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