英文:
Add an additional field while serializing
问题
在Serde序列化中，如何添加一个额外的字段：
#[derive(Serialize)]
struct X {
a: u32,
b: u32,
c: u32,
}
我想要在JSON序列化中添加一个名为 d，值为 "qwe" 的字段。如何在不从头开始编写X的序列化器的情况下实现这一目标？
英文:
In Serde serializers, how to add an additional field:
#[derive(Serialize)]
struct X {
a: u32,
b: u32,
c: u32,
}
I want to add to JSON serialization field d with value "qwe". How without writing completely a serializer for X from scratch?
答案1
得分: 6
自定义的Serialize实现并不算太糟糕：
use serde::ser::{Serialize, Serializer, SerializeStruct};
struct X {
a: u32,
b: u32,
c: u32,
}
impl Serialize for X {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
let mut x = serializer.serialize_struct("X", 4)?;
x.serialize_field("a", &self.a)?;
x.serialize_field("b", &self.b)?;
x.serialize_field("c", &self.c)?;
x.serialize_field("d", "qwe")?;
x.end()
}
}
如您所要求，这只是代码的翻译部分，没有其他内容。
英文:
A custom Serialize implementation isn't so bad:
use serde::ser::{Serialize, Serializer, SerializeStruct};
struct X {
a: u32,
b: u32,
c: u32,
}
impl Serialize for X {
fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
let mut x = serializer.serialize_struct("X", 4)?;
x.serialize_field("a", &self.a)?;
x.serialize_field("b", &self.b)?;
x.serialize_field("c", &self.c)?;
x.serialize_field("d", "qwe")?;
x.end()
}
}
答案2
得分: 4
假设您不介意字段 d 的存在，但只是不希望它在您的结构体中占用空间，您可以将其大小设为零，并在序列化时使用 serialize_with 属性来生成所需的数据：
#[derive(Serialize)]
struct X {
a: u32,
b: u32,
c: u32,
#[serde(serialize_with = "emit_qwe")]
d: (),
}
fn emit_qwe<S: Serializer>(_: &(), s: S) -> Result<S::Ok, S::Error> {
s.serialize_str("qwe")
}
英文:
Assuming that you don't mind that the field d exists, but you just don't want it taking space in your struct, you can make it zero-sized and use the serialize_with attribute to emit the desired data when serializing:
#[derive(Serialize)]
struct X {
a: u32,
b: u32,
c: u32,
#[serde(serialize_with = "emit_qwe")]
d: (),
}
fn emit_qwe<S: Serializer>(_: &(), s: S) -> Result<S::Ok, S::Error> {
s.serialize_str("qwe")
}
答案3
得分: 3
你可以创建一个单独的结构体，它使用 #[derive(Serialize)] 并将你的结构体的所有内容复制过去
impl Serialize for X {
fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
#[derive(Serialize)]
struct XSerialize {
a: u32,
b: u32,
c: u32,
d: &'static str,
}
XSerialize {
a: self.a,
b: self.b,
c: self.c,
d: "only at serialization"
}.serialize(serializer)
}
}
这样可以让你按照注释中指定的方式计算 d 的值。
英文:
You can create a separate struct that's #[derive(Serialize)] and copy everything in your struct over
impl Serialize for X {
fn serialize<S: serde::Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
#[derive(Serialize)]
struct XSerialize {
a: u32,
b: u32,
c: u32,
d: &'static str,
}
XSerialize {
a: self.a,
b: self.b,
c: self.c,
d: "only at serialization"
}.serialize(serializer)
}
}
This should allow you to compute a value for d as you specify in the comments.
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