Proto 3: A way to add metadata at field level

Question

I am using protobuf-gradle-plugin to generate java class from the proto files.

My proto file looks like

syntax = "proto3";

package com.address;
option java_package = "com.address";


message AddressesMessage {
 int32 id = 1;
 string address_line_1 = 4;
 string address_line_2 = 5;
 string city = 7;
 string postal_code = 9;
 string country = 10;
}

The plugin is generating classes for me but now I want to add some metadata information at field level. Like

syntax = "proto3";

package com.address;
option java_package = "com.address";


message AddressesMessage {
 int32 id = 1 [ (meta) = { isfact: false }];
 string address_line_1 = 4;
 string address_line_2 = 5;
 string city = 7;
 string postal_code = 9;
 string country = 10;
}

Is this possible?

score 1 · Accepted Answer · answered Mar 05 '20 at 07:25

1

Yes, that is possible via custom options, but: you'd need to define your custom options in a separate proto2 schema, which the proto3 schema then imports.

Something like (for your proto2 schema, untested):

syntax = "proto2";
import "google/protobuf/descriptor.proto";
package MetaPackage;
message MyMeta {
  optional bool isFact = 1;
}
extend google.protobuf.FieldOptions {
  optional MyMeta meta = 80412; // numbering: search for "One last thing" in the link above
}

then just add:

import "MyMeta.proto";

to your proto3 schema, and it should work. Accessing the metadata is another topic, though! See the link above.

answered Mar 05 '20 at 07:25

Marc Gravell

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Thanks @Marc Gravell . I followed the instructions and but I am getting an "Unresolved reference" error. – JDev Mar 05 '20 at 17:48
@jdev where? Which file/line etc? Is that the entire message? – Marc Gravell Mar 06 '20 at 06:54
Is it possible to define a Map as a custom option? Have asked the same on https://stackoverflow.com/questions/60982469/in-a-proto-how-can-i-define-a-map-as-a-custom-option – JDev Apr 02 '20 at 00:34
@JDev I do not believe so – Marc Gravell Apr 02 '20 at 08:32

Proto 3: A way to add metadata at field level

1 Answers1