Examining a protobuf message - how to get field values by name?

Question

I seem unable to find a way to verify the value of a field inside a protobuf message without explicitly invoking its getter.

I see examples around that make usage of Descriptors.FieldDescriptor instances to reach inside the message map, but they are either iterator-based or driven by field number.

Once I have the map:

Map<Descriptors.FieldDescriptor, Object> allFields = myMsg.getAllFields();

how can I get the value of field "fieldXyz"?

I know that I can use myMsg.getFieldXyz(), but this is not usable in a systematic way.

If there is no way to access field values by their names, I'd like to know what is the rationale behind this choice. I may have still to understand the protobuf "philosophy" :-)

score 40 · Accepted Answer · answered Jun 28 '16 at 09:27

40

I am not sure you are looking for Descriptors#findFieldByName(name). You can try with followings:

FieldDescriptor fieldDescriptor = message.getDescriptorForType().findFieldByName("fieldXyz");
Object value = message.getField(fieldDescriptor);

answered Jun 28 '16 at 09:27

Wilson

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This is going in a promising direction. How do I get to know which Java class I should cast the Object into? Looking at the API I only see methods that return `JavaType`, `Type` and similar. – Marco Faustinelli Jun 28 '16 at 10:04
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note that the `name` here is the name from the proto declaration, i.e. `field_xyz` rather than `fieldXyz` – AndyL Jan 12 '19 at 04:05
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is there any equivalent in python? – Amir Afianian May 08 '20 at 14:30

user5071787 · Answer 2 · 2018-12-06T07:33:08.917

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I know this is tagged for java but incase anyone is looking for a way to get the value in c++: (Assuming: field = FieldDescriptor* which contains a int32)

    int32_t value = message_1.GetReflection()->GetInt32(message_1, field);

It took me a while to get this and didn't find any stackoverflow references hence adding it. Hope it helps. Thanks!

edited Dec 06 '18 at 07:33

answered Dec 06 '18 at 05:34

user5071787

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Examining a protobuf message - how to get field values by name?

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