How to append object to a file while serializing using c# protobuf-net?

问题

I got a source code of Protobuf-net that serializes an object to a file.

var person = new Person {
        Id = 12345, Name = "Fred",
        Address = new Address {
            Line1 = "Flat 1",
            Line2 = "The Meadows"
        }
    };
    using (var file = File.Create("person.bin")) {
        ProtoBuf.Serializer.Serialize(file, person);
    }

But suppose i have two instance of Person that i want to serialize into a single file. how can i do that?

回答1:

protobuf, in the pure sense, does not have any "terminator" except the end of a file (this is so that objects can be merged/combined simply by concatenating the blobs).

However, we can inject our own markers, for example by prefixing every object with the length of the data that follows.

protobuf-net wraps this up by exposing a SerializeWithLengthPrefix method. There are various methods to deserialize from this, but the simplest is DeserializeItems, which gives you a streaming sequence of objects in turn (lazily spooling from the stream in the iterator - so it is perfectly suitable for very large sequences).

For info, so you can see how this is implemented: if you use PrefixStyle.Base128 and a positive fieldNumber, then on the wire this looks the same as if you had a wrapper object like:

[ProtoContract]
public class DoesNotExist {
    [ProtoMember({fieldNumber})]
    public List<Person> People {get;set;}
}

the key differences being that no actual DoesNotExist type/instance exists, and no List<T> is created - you just get the Person instances.

来源：https://stackoverflow.com/questions/15265698/how-to-append-object-to-a-file-while-serializing-using-c-sharp-protobuf-net

标签

file

serialization

protobuf-net