How to return an array in Protobuf service rpc

Question

I have the following schema in my .proto file:

service MyService {
    rpc GetItem (ItemQuery) returns (Item) {
    }
}

message ItemQuery {
    int id = 1;
}
message Item {
    int id = 1;
    string name = 2;
}

Now I want to add another rpc method to return multiple Items. Something like this:

rpc GetItems (ItemsQuery) returns (repeated Item) {
}

Is there a better way to do it than define an Items message?

Solution

Option 1 - Use stream:

rpc GetItems (ItemsQuery) returns (stream Item) {
}

Option 2 - Set a response message which will use a repeated object:

service MyService {
    rpc GetItem (ItemQuery) returns (ItemResponse) {
    }
}

message ItemQuery {
    int id = 1;
}
message ItemResponse {
    repeated Item items = 1;
}
message Item {
    int id = 1;
    string name = 2;
}

Comments

[LuMa]

I'm late for the party, but: Does option 2 have any advantages over option 1 or vice versa?

[Shoham]

Option 1 is a stream, it means you are returning an iterator and that means you can start processing the Items on client even before the server has finished sending all of them. Option 2 is a response object which contains a list of your Items. You can add some other properties to your ItemResponse (some metadata etc)...

[Jaward Sally]

Hi, Is there anyway we can return a key less array response as the response in gRPC? I tried stream, but it doesn't help.

[Vladimir]

Works wine with: message GetChannelsResponse {repeated string channel_name = 1;}