protobuf-net是否支持可空类型？

Question

是否可以在protobuf-net中生成可为空的成员？

message ProtoBuf1 {
    optional Int32? databit = 1;
    optional Nullable<bool> databool = 2;
}

Answer 1

是的，但如果您正在使用.proto执行codegen，则默认情况下它生成。

如果这只是C＃，当然，你没有需要 a .proto - 只是：

[ProtoContract]
public class ProgoBuf1
{
    [ProtoMember(1)]
    public int? Foo {get;set;}

    [ProtoMember(2)]
    public float? Bar {get;set;}
}

如果 在.proto工作，您可以考虑复制和编辑csharp.xslt以适合您的首选布局。

Answer 2

这是我使用Google的Protobuf .NET API时需要协议缓冲版本3的可空类型的解决方案。（请注意，这不是使用Marc Gravell的protobuf-net，所以这个并不是问题的确切答案。）

在NullableInt32.proto：

syntax = "proto3";

message NullableInt32 {
  int32 value = 1;
}

在NullableInt32Extensions.cs：

public static class NullableInt32Extensions
{
  public static bool HasValue(this NullableInt32 source)
  {
    return source != null;
  }
}

public partial class NullableInt32
{
  public static implicit operator int? (NullableInt32 other)
  {
    return other == null ? (int?)null : other.Value;
  }

  public static implicit operator NullableInt32(int? other)
  {
    return other == null ? null : new NullableInt32 { Value = other.Value };
  }
}

此模式可用于任何Protobuf非长度分隔的标量值 - double，float，int32，int64，uint32， uint64，sint32，sint64，fixed32，fixed64，sfixed32，sfixed64和bool。< / p>

以下是所有这些的工作原理。假设您有一条Record消息，其中包含NullableInt32字段，并且在这个设计示例中，它是唯一的字段。

在Record.proto：

syntax = "proto3";

import "NullableInt32.proto";

message Record {
  NullableInt32 id = 1;
}

使用Google protoc.exe将其编译为C＃后，您可以将Id属性视为与Nullable<int>几乎完全相同。

var r = new Record();

// r.Id is null by default, but we can still call HasValue()
// because extension methods work on null references.
r.Id.HasValue(); // => false

// We can explicitly set Id to null.
r.Id = null;

// We can set Id to a primitive numeric value directly
// thanks to our implicit conversion operators.
r.Id = 1;

// We can also use NullableInt32 in any context that expects a
// Nullable<int>. The signature of the following method is
// bool Equals(int?, int?).
Nullable.Equals<int>(r.Id, 1); // => true

// We can explicitly set Id to a NullableInt32.
r.Id = new NullableInt32 { Value = 1 };

// Just like Nullable<int>, we can get or set the Value of a
// NullableInt32 directly, but only if it's not null. Otherwise,
// we'll get a NullReferenceException. Use HasValue() to avoid this.
if(r.Id.HasValue())
  r.Id.Value.ToString(); // => "1"

// Setting Id to 0 is the same as setting Id to a new
// NullableInt32 since the default value of int32 is 0.
// The following expressions are equivalent.
r.Id = 0;
r.Id = new NullableInt32();
r.Id = new NullableInt32 { Value = 0 };
r.Id.Value = 0; // as long as Id is not null

最后，让我们看看我们的Record消息将如何通过网络传输，并使用Id的不同值。

var r = new Record();

// When Id is null, Record is empty since it has no other fields.
// Explicitly setting Id to null will have the same effect as
// never setting it at all.
r.Id = null;
r.ToByteArray(); // => byte[0]

// Since NullableInt32 is a Protobuf message, it's encoded as a
// length delimited type. Setting Id to 1 will yield four bytes.
// The first two indicate the type and length of the NullableInt32
// message, and the last two indicate the type and value held within.
r.Id = 1;
r.ToByteArray(); // => byte[] {
                 //      0x0a, // field  = 1, type = 2 (length delimited)
                 //      0x02, // length = 2
                 //      0x08, // field  = 1, type = 0 (varint)
                 //      0x01, // value  = 1
                 //    }

// When Id is set to the default int32 value of 0, only two bytes
// are needed since default values are not sent over the wire.
// These two bytes just indicate that an empty NullableInt32 exists.
r.Id = 0;
r.ToByteArray(); // => byte[] {
                 //      0x0a, // field  = 1, type = 2 (length delimited)
                 //      0x00, // length = 0
                 //    }

Answer 3

Proto 3

导入“ wrappers.proto”支持可为空的值：

• string（StringValue），
• int（Int32Value），
• bool（BoolValue）
• 等等

支持的类型的完整列表-https://docs.microsoft.com/en-us/dotnet/architecture/grpc-for-wcf-developers/protobuf-data-types#nullable-types

示例：

syntax = "proto3";
import "google/protobuf/wrappers.proto";

message ProtoPerson {
    google.protobuf.StringValue firstName = 1;
    google.protobuf.StringValue lastName = 2;
    google.protobuf.StringValue address1 = 3;
    google.protobuf.Int32Value age = 4;
}