How do I create a field mask for a field of a repeated field?

[Shelley Tong]

Let's say you have a proto defined as the following:

message Zoo {
    repeated Cat cats = 1;
}

Let's say cat looks like this:

message Cat {
    google.protobuf.StringValue name = 1
    Decimal age = 2;
}

If I want to reduce the amount of data in Zoo such that sample data only contains Cat with only the name field, how do I do that?

Example: A sample Zoo object will look like this:

{
    Cat: [{
        name = "sam";
    },
    {
        name = "hester";
    }]
}

I'm trying to do this with one field mask:

FieldMask zoo_mask = FieldMask.newBuilder()
    .addPaths("cats")
    .build();

Zoo getMaskedZoo(FieldMask mask, Zoo zoo) {
    Zoo.Builder zooDest = Zoo.newBuilder();
    FieldMaskUtil.merge(zoo_mask, zoo, zooDest);
    return zooDest.build();
}

How do I make it so that only the name displays for each Cat?

[Feng Xiao]

This is not supported at the moment, i.e., you can't use 'cats.name' in the FieldMask because 'cats' is a repeated field. FieldMaskUtil is more of a helper utility for a specific use case of protobuf. In your case, I think you can simply use protobuf reflection API to do the same.

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