Deriving JsonSchema with Fields Using Custom Serialization
Serde allows you to change how a field is (de)serialized by setting a #[serde(with = "path")]
attribute, where $path::serialize
and $path::deserialize
must be functions with the correct signature. Schemars supports the same attribute, but path
must be a type implementing JsonSchema
.
In order to derive JsonSchema
on a type which includes a #[serde(with = "path")]
attribute where path
is not a type implementing JsonSchema
, you'll need to override it with a suitable #[schemars(with = "Type")]
or #[schemars(schema_with = "path")]
attribute.
use schemars::schema::{Schema, SchemaObject};
use schemars::{gen::SchemaGenerator, schema_for, JsonSchema};
use serde::{Deserialize, Serialize};
// `int_as_string` and `bool_as_string` use the schema for `String`.
#[derive(Default, Deserialize, Serialize, JsonSchema)]
pub struct MyStruct {
#[serde(default = "eight", with = "as_string")]
#[schemars(with = "String")]
pub int_as_string: i32,
#[serde(default = "eight")]
pub int_normal: i32,
#[serde(default, with = "as_string")]
#[schemars(schema_with = "make_custom_schema")]
pub bool_as_string: bool,
#[serde(default)]
pub bool_normal: bool,
}
fn make_custom_schema(gen: &mut SchemaGenerator) -> Schema {
let mut schema: SchemaObject = <String>::json_schema(gen).into();
schema.format = Some("boolean".to_owned());
schema.into()
}
fn eight() -> i32 {
8
}
// This module serializes values as strings
mod as_string {
use serde::{de::Error, Deserialize, Deserializer, Serializer};
pub fn serialize<T, S>(value: &T, serializer: S) -> Result<S::Ok, S::Error>
where
T: std::fmt::Display,
S: Serializer,
{
serializer.collect_str(value)
}
pub fn deserialize<'de, T, D>(deserializer: D) -> Result<T, D::Error>
where
T: std::str::FromStr,
D: Deserializer<'de>,
{
let string = String::deserialize(deserializer)?;
string
.parse()
.map_err(|_| D::Error::custom("Input was not valid"))
}
}
fn main() {
let schema = schema_for!(MyStruct);
println!("{}", serde_json::to_string_pretty(&schema).unwrap());
}
Click to see the output JSON schema...
{
"$schema": "http://json-schema.org/draft-07/schema#",
"title": "MyStruct",
"type": "object",
"properties": {
"bool_as_string": {
"default": "false",
"type": "string",
"format": "boolean"
},
"bool_normal": {
"default": false,
"type": "boolean"
},
"int_as_string": {
"default": "8",
"type": "string"
},
"int_normal": {
"default": 8,
"type": "integer",
"format": "int32"
}
}
}
Note that the default
values in the schema are serialized as strings where appropriate.