Here's how you could set that nested field in your example (this code is
untested so may not work exactly, but should be pretty close):
const FieldDescriptor* health_report_field =
parent.GetDescriptor()->FindFieldByName("healthreport");
Message* health_report = parent.GetReflection()->MutableMessage(&parent,
health_report_field);
const FieldDescriptor* os_field =
health_report->GetDescriptor()->FieldFieldByName("os");
Message* os = health_report->GetReflection()->MutableMessage(health_report,
os_field);
const FieldDescriptor* version_field =
os->GetDescriptor()->FindFieldByName("version");
os->GetReflection()->SetEnumValue(os, version_field, 3);
On Tue, Jun 22, 2021 at 11:34 AM J G <[email protected]> wrote:
> Hi Adam,
>
> OK, but would I need to know the fields in the message ahead of time? That
> is what I am trying to avoid.
> The paths of the nested messages are in a table, such as
>
> "healthreport/os/version", 3
>
> So the healthreport variable is allocated, and it contains a component
> called os, which itself contains a field called version.
>
> So I am trying to write a generic enum function, that can descend the
> parent, and guided by the path info, can resolve the value that needs to be
> stored there, but if I am to traverse the entire tree manually, how does
> the reflection API help?
> On Tuesday, 22 June 2021 at 14:21:59 UTC-4 [email protected] wrote:
>
>> I think the reason this is getting tricky is because you're trying to
>> traverse the descriptors first and then look at the message tree afterward.
>> I would expect it to be much easier if you traverse the message and look at
>> the descriptors at the same time.
>>
>> On Tue, Jun 22, 2021 at 10:58 AM J G <[email protected]> wrote:
>>
>>> Hi Adam,
>>>
>>> That works for the first iteration, but I descend the tree like so:
>>>
>>> bool enumpb( const char * pszpath, ENUMPROTOPROC f, const
>>> google::protobuf::Descriptor * d, uintptr_t param ) {
>>>
>>> std::string path = pszpath;
>>>
>>> for ( int i = 0; i < d->field_count(); i++ ) {
>>>
>>> auto field = d->field( i );
>>>
>>> std::string localpath = pszpath;
>>>
>>> if ( 0 != strcmp( "component", field->name().c_str() ) ) {
>>>
>>> localpath.append( field->name() );
>>>
>>> }
>>>
>>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() ) ) {
>>>
>>> if ( f && ! f( field, localpath.c_str(), param ) ) {
>>>
>>> return false;
>>>
>>> }
>>>
>>> }
>>>
>>> auto mt = field->message_type();
>>>
>>> if ( ! mt ) {
>>>
>>> continue;
>>>
>>> } else if ( 0 != strcmp( d->full_name().c_str(),
>>> mt->full_name().c_str() ) ) {
>>>
>>> std::string localpath2 = localpath;
>>>
>>> if ( ( ! localpath.empty() ) && ( '/' != localpath.back() )
>>> ) {
>>>
>>> localpath2.append( "/" );
>>>
>>> }
>>>
>>> if ( ! enumpb( hp, report, localpath2.c_str(), f, mt, param
>>> ) ) {
>>>
>>> return false;
>>>
>>> }
>>>
>>> } else {
>>>
>>> // printf( "Skipping circular %s" EOL, d->full_name().c_str()
>>> );
>>>
>>> }
>>>
>>> }
>>>
>>> return true;
>>>
>>> }
>>>
>>> So I start the traversal like this:
>>>
>>> auto d = report->GetDescriptor();
>>>
>>> enumpb( "", f, d, param );
>>>
>>> And it goes down the variable, visiting each leaf and nested child
>>> variable, but I can't address each nested child directly that way, can I?
>>> The mt variable does hold the descriptor for each nested variable at
>>> some point, but I don't know how I'd derive the variable's instance from it.
>>>
>>> On Tuesday, 22 June 2021 at 13:47:15 UTC-4 [email protected] wrote:
>>>
>>>> I think the easiest thing would be that wherever you're now storing a
>>>> google::protobuf::FieldDescriptor*, you can also store a
>>>> google::protobuf::Message* pointing to the parent message.
>>>>
>>>> On Tue, Jun 22, 2021 at 10:41 AM J G <[email protected]> wrote:
>>>>
>>>>> Hi Adam,
>>>>>
>>>>> Yes, the HealthReport variable is the parent, and it contains a
>>>>> HardwareComponent variable, but I am enumerating the from the parent,
>>>>> meaning I am trying to not hard-code the structure of the contained items.
>>>>>
>>>>> So how would I obtain a pointer to the message for each leaf without
>>>>> hard-coding the member names in there?
>>>>>
>>>>> I am able to figure out what value I want to set in each leaf by a map
>>>>> I have that uses the field's path to match it to the value I want to
>>>>> store.
>>>>>
>>>>> On Tuesday, 22 June 2021 at 13:33:11 UTC-4 [email protected] wrote:
>>>>>
>>>>>> So is it correct that HealthReport is the top-level message type and
>>>>>> HardwareComponent is nested somewhere within that? I think what you're
>>>>>> trying to do is doable, but when you call reflection->SetString(), you
>>>>>> have
>>>>>> to pass the immediate parent message containing the field, not the
>>>>>> top-level message. You don't need to save the descriptor for each leaf,
>>>>>> but
>>>>>> you do need to save a pointer to the message containing each leaf.
>>>>>>
>>>>>> On Tue, Jun 22, 2021 at 10:17 AM J G <[email protected]> wrote:
>>>>>>
>>>>>>> Hi again Adam, and thank you for taking the time to help me.
>>>>>>>
>>>>>>> Maybe I haven't explained what I am trying to do properly.
>>>>>>>
>>>>>>> I have a protobuf variable, which itself is composed of more nested
>>>>>>> variables.
>>>>>>>
>>>>>>> I am enumerating the fields of the variable.
>>>>>>>
>>>>>>> Where the item is a leaf, the field is a simple c-like type (int,
>>>>>>> bool, string, etc)
>>>>>>>
>>>>>>> Where the item itself has fields, it is an agglomerate type and it
>>>>>>> is descended recursively.
>>>>>>>
>>>>>>> My aim is to set each leaf programmatically.
>>>>>>>
>>>>>>> So as I traverse the arborescance, I am collecting the field
>>>>>>> definitions for the leafs.
>>>>>>>
>>>>>>> So later, I am addressing the variable again, but trying to set one
>>>>>>> of its leafs by the field definition I saved. Do I also have to save the
>>>>>>> descriptor for each leaf?
>>>>>>>
>>>>>>> Can what I want to do be done?
>>>>>>>
>>>>>>>
>>>>>>> On Tuesday, 22 June 2021 at 11:52:00 UTC-4 [email protected] wrote:
>>>>>>>
>>>>>>>> It looks to me like r->report points to a vafmsg.HealthReport but
>>>>>>>> the field descriptor refers to a field in another message
>>>>>>>> (vafmsg.HardwareComponent).
>>>>>>>>
>>>>>>>> On Tue, Jun 22, 2021 at 7:42 AM J G <[email protected]> wrote:
>>>>>>>>
>>>>>>>>> Hello Adam,
>>>>>>>>>
>>>>>>>>> OK, I understand, so I've tried this, but I get an error.
>>>>>>>>>
>>>>>>>>> void my_set_value( class healthreport * r, const char *
>>>>>>>>> defaultvalue, const google::protobuf::FieldDescriptor * descriptor ) {
>>>>>>>>>
>>>>>>>>> auto reflection = r->report->GetReflection();
>>>>>>>>>
>>>>>>>>> switch( descriptor->type() ) {
>>>>>>>>> case google::protobuf::FieldDescriptor::TYPE_STRING: {
>>>>>>>>>
>>>>>>>>> printf( "REQUESTED TYPE: STRING" EOL );
>>>>>>>>> std::string s = defaultvalue;
>>>>>>>>> reflection->SetString( r->report, descriptor, s );
>>>>>>>>>
>>>>>>>>> }
>>>>>>>>> break;
>>>>>>>>>
>>>>>>>>> default:
>>>>>>>>>
>>>>>>>>> printf( "REQUESTED TYPE %d NOT HANDLED" EOL,
>>>>>>>>> descriptor->type() );
>>>>>>>>> break;
>>>>>>>>>
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> }
>>>>>>>>> Running the above produces the following output:
>>>>>>>>>
>>>>>>>>> REQUESTED TYPE: STRING
>>>>>>>>> [libprotobuf FATAL
>>>>>>>>> /var/tmp/portage/dev-libs/protobuf-3.15.8/work/protobuf-3.15.8/src/google/protobuf/generated_message_reflection.cc:111]
>>>>>>>>> Protocol Buffer reflection usage error:
>>>>>>>>> Method : google::protobuf::Reflection::SetString
>>>>>>>>> Message type: vafmsg.HealthReport
>>>>>>>>> Field : vafmsg.HardwareComponent.hardware_interface
>>>>>>>>> Problem : Field does not match message type.
>>>>>>>>> terminate called after throwing an instance of
>>>>>>>>> 'google::protobuf::FatalException'
>>>>>>>>> what(): Protocol Buffer reflection usage error:
>>>>>>>>> Method : google::protobuf::Reflection::SetString
>>>>>>>>> Message type: vafmsg.HealthReport
>>>>>>>>> Field : vafmsg.HardwareComponent.hardware_interface
>>>>>>>>> Problem : Field does not match message type.
>>>>>>>>>
>>>>>>>>> Here is the proto definition of the variable triggering the
>>>>>>>>> exception:
>>>>>>>>>
>>>>>>>>> message HardwareComponent {
>>>>>>>>> optional Component component = 1;
>>>>>>>>> repeated DiscreteValue temp = 2;
>>>>>>>>> optional string hardware_interface = 3;
>>>>>>>>> optional uint32 remaining_life = 4;
>>>>>>>>> optional uint32 total_hours = 5;
>>>>>>>>> optional EnergyInfo energy = 6;
>>>>>>>>> }
>>>>>>>>>
>>>>>>>>> So the type really IS string, yet an exception is triggered...
>>>>>>>>>
>>>>>>>>> What am I doing wrong?
>>>>>>>>>
>>>>>>>>> On Friday, 18 June 2021 at 17:56:57 UTC-4 [email protected]
>>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>> Each descriptor describes part of the schema (e.g. a message
>>>>>>>>>> type, enum type, etc.) but is unrelated to any particular instance
>>>>>>>>>> of it.
>>>>>>>>>> As a result, if you have a descriptor by itself then you can't really
>>>>>>>>>> modify anything because you separately need an instance of the thing
>>>>>>>>>> you
>>>>>>>>>> want to modify. The way to programmatically modify a message is to
>>>>>>>>>> use the
>>>>>>>>>> Reflection
>>>>>>>>>> <https://github.com/protocolbuffers/protobuf/blob/9d9d8ee18dedfb18371031cd299d1d282ddf707f/src/google/protobuf/message.h#L452>
>>>>>>>>>> API. You can use Reflection::ListFields() to get a list of all the
>>>>>>>>>> fields
>>>>>>>>>> that are set on the message and then there are Reflection::Get* and
>>>>>>>>>> Reflection::Set* methods to get and set particular fields.
>>>>>>>>>>
>>>>>>>>>> On Fri, Jun 18, 2021 at 9:11 AM J G <[email protected]> wrote:
>>>>>>>>>>
>>>>>>>>>>> Hi,
>>>>>>>>>>>
>>>>>>>>>>> I've got some code that lets me recursively walk a protobuf
>>>>>>>>>>> variable.
>>>>>>>>>>>
>>>>>>>>>>> That part works, I can enumerate the characteristics of a
>>>>>>>>>>> variable, but the pointers/references returned by the API are const.
>>>>>>>>>>>
>>>>>>>>>>> My question is: From a variable's Descriptor or FieldDescriptor,
>>>>>>>>>>> is it possible to get a non-const pointer/reference to the field to
>>>>>>>>>>> be able
>>>>>>>>>>> to modify it?
>>>>>>>>>>>
>>>>>>>>>>> Here's my (simplified) code so far:
>>>>>>>>>>>
>>>>>>>>>>> void enumpb( const google::protobuf::Descriptor * d ) {
>>>>>>>>>>>
>>>>>>>>>>> for ( int i = 0; i < d->field_count(); i++ ) {
>>>>>>>>>>>
>>>>>>>>>>> auto field = d->field( i );
>>>>>>>>>>>
>>>>>>>>>>> // Modify variable code here
>>>>>>>>>>> [...]
>>>>>>>>>>>
>>>>>>>>>>> auto mt = field->message_type();
>>>>>>>>>>> if ( ! mt ) {
>>>>>>>>>>> continue;
>>>>>>>>>>> } else if ( 0 != strcmp( d->full_name().c_str(),
>>>>>>>>>>> mt->full_name().c_str() ) ) {
>>>>>>>>>>>
>>>>>>>>>>> enumpb( mt ) ;
>>>>>>>>>>>
>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>> return true;
>>>>>>>>>>>
>>>>>>>>>>> }
>>>>>>>>>>>
>>>>>>>>>>> --
>>>>>>>>>>> You received this message because you are subscribed to the
>>>>>>>>>>> Google Groups "Protocol Buffers" group.
>>>>>>>>>>> To unsubscribe from this group and stop receiving emails from
>>>>>>>>>>> it, send an email to [email protected].
>>>>>>>>>>> To view this discussion on the web visit
>>>>>>>>>>> https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com
>>>>>>>>>>> <https://groups.google.com/d/msgid/protobuf/dcf6bb53-24ce-4404-ab71-0fe3a94adc40n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>>>>>>>> .
>>>>>>>>>>>
>>>>>>>>>> --
>>>>>>>>> You received this message because you are subscribed to the Google
>>>>>>>>> Groups "Protocol Buffers" group.
>>>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>>>> send an email to [email protected].
>>>>>>>>>
>>>>>>>> To view this discussion on the web visit
>>>>>>>>> https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com
>>>>>>>>> <https://groups.google.com/d/msgid/protobuf/7ef6e77e-8635-4b16-b570-b80f75d207d9n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>>>>>> .
>>>>>>>>>
>>>>>>>> --
>>>>>>> You received this message because you are subscribed to the Google
>>>>>>> Groups "Protocol Buffers" group.
>>>>>>> To unsubscribe from this group and stop receiving emails from it,
>>>>>>> send an email to [email protected].
>>>>>>>
>>>>>> To view this discussion on the web visit
>>>>>>> https://groups.google.com/d/msgid/protobuf/39fd7a89-426a-453d-9482-4cb3e3658da0n%40googlegroups.com
>>>>>>> <https://groups.google.com/d/msgid/protobuf/39fd7a89-426a-453d-9482-4cb3e3658da0n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>>>> .
>>>>>>>
>>>>>> --
>>>>> You received this message because you are subscribed to the Google
>>>>> Groups "Protocol Buffers" group.
>>>>> To unsubscribe from this group and stop receiving emails from it, send
>>>>> an email to [email protected].
>>>>>
>>>> To view this discussion on the web visit
>>>>> https://groups.google.com/d/msgid/protobuf/764459e6-6f37-42aa-869c-0f8405aa13c6n%40googlegroups.com
>>>>> <https://groups.google.com/d/msgid/protobuf/764459e6-6f37-42aa-869c-0f8405aa13c6n%40googlegroups.com?utm_medium=email&utm_source=footer>
>>>>> .
>>>>>
>>>> --
>>> You received this message because you are subscribed to the Google
>>> Groups "Protocol Buffers" group.
>>> To unsubscribe from this group and stop receiving emails from it, send
>>> an email to [email protected].
>>>
>> To view this discussion on the web visit
>>> https://groups.google.com/d/msgid/protobuf/3d9ed924-341b-43cf-8359-c91a93d1916dn%40googlegroups.com
>>> <https://groups.google.com/d/msgid/protobuf/3d9ed924-341b-43cf-8359-c91a93d1916dn%40googlegroups.com?utm_medium=email&utm_source=footer>
>>> .
>>>
>> --
> You received this message because you are subscribed to the Google Groups
> "Protocol Buffers" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to [email protected].
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/protobuf/9c617cbc-f632-46a3-a1ac-c95c7fe6d2e2n%40googlegroups.com
> <https://groups.google.com/d/msgid/protobuf/9c617cbc-f632-46a3-a1ac-c95c7fe6d2e2n%40googlegroups.com?utm_medium=email&utm_source=footer>
> .
>
--
You received this message because you are subscribed to the Google Groups
"Protocol Buffers" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/protobuf/CADqAXr6AuJ77sZ44o6%3DseYguf3ReMbywOO7tEBVgnRgGmW0b8A%40mail.gmail.com.
