Yes, this is correct: protobuf-net cannot successfully round-trip a get-only property such as your ClientId, and so will throw an exception trying to construct a contract that explicitly requires such a property to be serialized.
It is not alone in this limitation. I notice that you are marking your type with data contract attributes. If I try to serialize an instance of it with DataContractSerializer, it fails with an equivalent exception:
System.Runtime.Serialization.InvalidDataContractException was caught
Message="No set method for property 'ClientId' in type 'Question40276317.V1.TestMessage'."
Source="System.Runtime.Serialization"
If you simply want to skip get-only properties then mark them with [IgnoreDataMember]. If you want to serialize and deserialize them successfully, you have the following options.
Firstly, protobuf-net needs to be able to construct your object. Unlike Json.NET it will not call a parameterized constructor so the simplest thing to do is to add a parameterless constructor. It could be private or protected (on the full framework) as long as it exists. Alternatively you could set [ProtoContract(SkipConstructor = true)], however that doesn't work on all frameworks or in partial trust situations.
Next, you need to make the properties settable somehow. One solution would be to add private setters:
[DataContract]
public class TestMessage
{
private int clientId;
[DataMember(Order = 1)]
public int ClientId
{
get { return clientId; }
private set { clientId = value; }
}
private string name;
[DataMember(Order = 2)]
public string Name
{
get { return name; }
private set { name = value; }
}
protected TestMessage() { }
public TestMessage(int clientId, string name)
{
this.clientId = clientId;
this.name = name;
}
}
Another would be to mark the underlying fields rather than the properties with data contract attributes:
[DataContract]
public class TestMessage
{
[DataMember(Name = "ClientId", Order = 1)]
private int clientId;
public int ClientId
{
get { return clientId; }
}
[DataMember(Name = "Name", Order = 2)]
private string name;
public string Name
{
get { return name; }
}
protected TestMessage() { }
public TestMessage(int clientId, string name)
{
this.clientId = clientId;
this.name = name;
}
}
Alternatively, if you really want the values for clientId and name to be immutable after construction, you're going to need a serialization surrogate, like so:
public class TestMessage
{
private readonly int clientId;
public int ClientId
{
get { return clientId; }
}
private readonly string name;
public string Name
{
get { return name; }
}
public TestMessage(int clientId, string name)
{
this.clientId = clientId;
this.name = name;
}
}
[DataContract]
internal class TestMessageSurrogate
{
public static implicit operator TestMessageSurrogate(TestMessage message)
{
if (message == null)
return null;
return new TestMessageSurrogate { ClientId = message.ClientId, Name = message.Name };
}
public static implicit operator TestMessage(TestMessageSurrogate message)
{
if (message == null)
return null;
return new TestMessage(message.ClientId, message.Name);
}
[DataMember(Order = 1)]
public int ClientId { get; set; }
[DataMember(Order = 2)]
public string Name { get; set; }
}
Then, before serialization, do:
ProtoBuf.Meta.RuntimeTypeModel.Default.Add(typeof(TestMessage), true).SetSurrogate(typeof(TestMessageSurrogate));
By using a surrogate, you also avoid the need for any parameterless constructor.
