Updating Firestore documents in Golang using structs (or protobuf messages) as data

Question

Given the following API:

syntax = "proto3";

service FooService {
  rpc UpdateFoo(UpdateFooRequest) returns (Foo) {}
}

message Foo {
  string name = 1;
  string description = 2;
  string action = 3;
}

message UpdateFooRequest {
  Foo foo = 1;
  // The list of fields to be updated. For the `FieldMask` definition,
  // see https://developers.google.com/protocol-buffers/docs/reference/google.protobuf#fieldmask
  google.protobuf.FieldMask update_mask = 2;
}

This API talks to a backend Firestore "foos" collection.
The implementation is in Golang. The firestore package has an Update() method, but it requires to provide a list of firestore.Update structs:

type Update struct {
    Path      string // Will be split on dots, and must not contain any of "˜*/[]".
    FieldPath FieldPath
    Value     interface{}
}

I have problems writing the implementation of the RPC UpdateFoo: I cannot easily construct the firestore.Update struct. At the same time, I want to ensure that the paths provided in the update_mask are valid.

This is what I am trying:

func (s *Server) UpdateFoo(ctx context.Context, req *pb.UpdateFooRequest) (*pb.Foo, error) {

var updates []firestore.Update
// Loop all paths in the update_mask
for _, p := range req.GetUpdateMask().GetPaths() {
   // Check that path is valid field of Foo message.
   // How to do this?
   ...
   ...
   if path is not valid {
       return nil, status.Errorf(codes.InvalidArgument, "invalid path %s", p)
   }
   // When path is valid, I need to take the value from the req.GetFoo() message
   // How to do this?
   newValue := req.GetFoo().Get????<this is p variable>

   update = append(update, &firestore.Update{Path: p, Value: newValue}
}

Any hints would be greatly appreciated.

Answer 1

I ran into a similar issue trying to use firestore along with protobuf in Golang. There does not seem to be support for using proto field masks and structs to do updates.

Here's a workaround with Set and fieldmask-utils:

import (
  "github.com/golang/protobuf/protoc-gen-go/generator"
  fieldmask_utils "github.com/mennanov/fieldmask-utils"
)

var (
  id      string
  request UpdateFooRequest
)

mask, err: = fieldmask_utils.MaskFromProtoFieldMask(request.FieldMask, generator.CamelCase)
// handle err...

m := make(map[string]interface{}) // a map to copy to
err := fieldmask_utils.StructToMap(mask, request.Foo, m)
// handle err..

_, err = r.client.Collection(r.collection).Doc(id).Set(ctx, m, firestore.MergeAll)
// handle err..