On Tue, May 17, 2016 at 1:49 AM, Denis Bakhvalov <dendib...@gmail.com>
wrote:
> Hi Feng Xiao,
>
> Thanks for your reply!
>
> Unfortunately I couldn't find good examples how to use it, so let me ask
> one more question:
>
> Should I put mask as a part of original message:
>
> message RepAndOpt
> {
> repeated string name = 1;
> string surname = 2;
>
> google.protobuf.FieldMask field_mask = 3;
> }
>
> or put it as standalone message?
>
> message RepAndOptMask
> {
> google.protobuf.FieldMask field_mask = 1;
> }
>
> I think there is nothing wrong if I will send them separately, right?
>
It's probably more clear to put it separately from the original message
it's applied to, but either one works.
>
> понедельник, 16 мая 2016 г., 22:14:33 UTC+2 пользователь Feng Xiao написал:
>>
>>
>>
>> On Wed, May 11, 2016 at 5:09 AM, Denis Bakhvalov <dend...@gmail.com>
>> wrote:
>>
>>> Hi,
>>>
>>> Suppose I have such message structure:
>>>
>>>
>>> package msg_RepAndOpt;
>>>
>>> message RepAndOpt{
>>> repeated string name = 1;
>>> optional string surname = 2;
>>> ...
>>> // there are lots of others.}
>>>
>>>
>>> And I have two components that have copies of this message:
>>>
>>>
>>> // component1:RepAndOpt A;
>>> A.add_name("Name");
>>> A.set_surname("Surname");
>>> // component2:RepAndOpt B;
>>>
>>>
>>> In my case components modify those messages via transaction mechanism.
>>> It means that if one component changes some field it also sends it to
>>> another component to propagate those changes. Component-receiver is doing
>>> merge:
>>>
>>>
>>> // Component2 modifies B and sends it to component1.// Component1 perfoms
>>> merge:
>>> A.MergeFrom(B);
>>>
>>>
>>> Now, say, component2 wants to erase field "name". If it will send clear
>>> B message (default construction) than:
>>>
>>> - - MergeFrom() will not modify A;
>>> - - CopyFrom() will erase also other fields.
>>>
>>> Another way will be to fill B with the contents of A, clear name field
>>> and component1 will use CopyFrom(). But this is not acceptable because
>>> system is really high-loaded and there could be lots of other fields. So,
>>> desired solution to clean name field is:
>>>
>>> 1. 1. Component2 create B message.
>>> 2. 2. Explicitly stores information that it want to erase only name
>>> field.
>>> 3. 3. Component1 perform A.MergeFrom(B).
>>> 4. 4. Result: A::name is cleared but other fields are left untouched.
>>>
>>> As far as I tested this applies to repeated and optional fields. Is
>>> there any ready-to-use solution or I should modify protobuf implementation?
>>>
>> I think you can do this using FieldMaskUtil:
>>
>> https://github.com/google/protobuf/blob/beta-3/src/google/protobuf/util/field_mask_util.h#L111
>>
>> You create an empty B message along with a FieldMask containing only the
>> field you want to clear, and use FieldMaskUtil::MergeMessageTo(A,
>> field_mask, &B) to replace the field in A with the value from B.
>>
>>
>>
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>>
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