在protobuf-net中是否可能生成可为空的成员?
message ProtoBuf1 {
optional Int32? databit = 1;
optional Nullable<bool> databool = 2;
}
在protobuf-net中是否可能生成可为空的成员?
message ProtoBuf1 {
optional Int32? databit = 1;
optional Nullable<bool> databool = 2;
}
是的,但如果你是从.proto进行代码生成,它默认不会生成它们。
如果只是C#,当然,您不需要.proto - 只需:
[ProtoContract]
public class ProgoBuf1
{
[ProtoMember(1)]
public int? Foo {get;set;}
[ProtoMember(2)]
public float? Bar {get;set;}
}
如果你是从.proto文件工作,你可以考虑复制并编辑csharp.xslt以适应你喜欢的布局。
[DefaultValue(...)]
可能不起作用,但你可以使用 [ProtoMember(n)] public DateTime Foo {get;set;} = yourDefault; public bool ShouldSerializeFoo() => Foo != yourDefault;
。 - Marc Gravell这是我在使用 Google 的 Protobuf .NET API 时针对可空类型的解决方案,该 API 要求使用 Protocol Buffers 版本 3(请注意,这不是使用 Marc Gravell 的 protobuf-net,因此这不是对所提问问题的确切回答)。
在 NullableInt32.proto
中:
syntax = "proto3";
message NullableInt32 {
int32 value = 1;
}
在NullableInt32Extensions.cs
中:
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 };
}
}
这个模式可以用于任何非长度限制的Protobuf纯量值,包括double
、float
、int32
、int64
、uint32
、uint64
、sint32
、sint64
、fixed32
、fixed64
、sfixed32
、sfixed64
和bool
。
以下是它的工作原理。假设你有一个名为Record
的消息,其中包含一个NullableInt32
字段,在这个假想的示例中,它是唯一的字段。
在Record.proto
文件中:
syntax = "proto3";
import "NullableInt32.proto";
message Record {
NullableInt32 id = 1;
}
使用Google的protoc.exe
将此编译为C#后,您可以几乎像使用Nullable<int>
一样处理Id
属性。
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,让我们看看当Id
的值不同时,我们的Record
消息将如何通过网络传输。
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
// }
导入 "wrappers.proto" 支持可为空的值:
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;
}