The Official documentation about map type says:
map<key_type, value_type> map_field = N;
...where the key_type can be any integral or string type (so, any scalar type except for floating point types and bytes). The value_type can be any type.
I want to define a map<string, repeated string>
field, but it seems illegal on my libprotoc 3.0.0
, which complains Expected ">"
. So I wonder if there is any way to put repeated string into map.
A Possible workaround could be:
message ListOfString {
repeated string value = 1;
}
// Then define:
map<string, ListOfString> mapToRepeatedString = 1;
But ListOfString
here looks redundant.
I had the same need, and got the same error. I do not believe this is possible. Here is the relevant BNF definitions from the language specification.
https://developers.google.com/protocol-buffers/docs/reference/proto3-spec
messageType = [ "." ] { ident "." } messageName
mapField = "map" "<" keyType "," type ">" mapName "=" fieldNumber [ "["fieldOptions "]" ] ";"
type = "double" | "float" | "int32" | "int64" | "uint32" | "uint64"
| "sint32" | "sint64" | "fixed32" | "fixed64" | "sfixed32" | "sfixed64"
| "bool" | "string" | "bytes" | messageType | enumType
messageName = ident
ident = letter { letter | decimalDigit | "_" }
field = [ "repeated" ] type fieldName "=" fieldNumber [ "[" fieldOptions "]" ] ";"
"repeated" keyword only appears in the field definition. The map definition requires a "type", which does not include the repeated keyword.
That means there are a few options.
message MapFieldEntry { key_type key = 1; repeated value_type value = 2; } repeated MapFieldEntry map_field = N;You would need to convert the data to a map yourself, but this should be fairly trivial in most languages. In Java:
List<MapFieldEntry> map_field = // Existing list from protobuf. Map<key_type, List<value_type>> = map_field.stream() .collect(Collectors.toMap(kv -> kv.key, kv -> kv.value));