Message.Builder and sub-builders

[Alex]

Let's assume we have the following structure:

message Alpha {

  message Beta {

    

    optional int32 mercury = 1;

    

    optional int32 venus = 2;

  }

  optional int32 earth = 1;

  optional Beta mars = 2;

}

The Java generated code allows to get a sub-builder for "mars" field from a builder for an Alpha message by calling Alpha.newBuilder().getMarsBuilder(). This is nice because I can keep builders for structured messages and update them as needed and build the Alpha message as needed, but still hold on to the big builder which I plan to update further.

But I do not think there is a way to do this in a generic way, using Message.Builder interface. Is there any plan for something like this?

[Jason Hsueh]

Do you mean getting the sub-builders by passing the Descriptor.FieldDescriptor for the field you want, like what you would do for Message.Builder.setField()? This sounds like a reasonable feature request, though to be honest I'm not familiar enough with the Java code to know how difficult this would be.

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[Alex]

Yes. For example by calling messageBuilder.getBuilder(marsFieldDescriptor) I would get a builder for the mars field which stays attached to the messageBuilder.

At the moment one can call Message.Builder.newBuilder(Descriptors.FieldDescriptor)  in a generic way to create a new sub-builder, but this new builder is detached from the parent builder. So one cannot have a compare complex structure of  builders to handle in a generic way. But the same thing works when handing messages in non-generic way.