Deserializing JSON array containing different types of object

Question

So I have a JSON that looks like this :

{
  "name": "customer",
  "properties": [
    {
      "name": "id",
      "type": "int",
      "value": 32
    },
    {
      "name": "name",
      "type": "string",
      "value": "John"
    }
  ]
}

Currently I am deserializing to this set of struct :

#[derive(Serialize, Deserialize, Debug)]
struct Customer {
    name: String,
    properties: Vec<Property>,
}

#[derive(Serialize, Deserialize, Debug)]
#[serde(tag = "name", content = "value")]
enum Property {
    #[serde(rename = "id")]
    Id(i32),
    #[serde(rename = "name")]
    Name(String),
}

But to avoid dealing with matching over enum every time I want to access a property I would like to deserialize it to a struct that looks like this :

struct Customer {
  name: String,
  properties: Properties,
}

struct Properties {
  id: i32, // will be 32 as in the object containing the name "id".
  name: String, // will be John as in the object containing the name "name".
}

Is this something that the serde library allow in some way ? If so could you provide an example on how to achieve that ?

Note that I can't mess with the actual json structure so I am not interested in any solutions that requires that.

edkeveked · Accepted Answer · 2020-09-24 17:58:18Z

By using a custom deserializer as follows

extern crate serde_json; // 1.0.32
extern crate serde; // 1.0.80
#[macro_use] extern crate serde_derive;

use serde::de::{Deserializer, SeqAccess, Visitor};
use std::fmt;


#[derive(Serialize, Deserialize)]
struct Customer {
    name: String,
    #[serde(deserialize_with = "parse_property")]
    properties: Property,
}

// #[derive(Default, Debug, Deserialize)]
#[derive(Default, Serialize, Deserialize, Debug)]
struct Property {
    id: i32,
    name: String,
}

#[derive(Default, Serialize, Deserialize, Debug)]
struct Key {
    name: String,
    value: i32,
}

#[derive(Default, Serialize, Deserialize, Debug)]
struct Val {
    name: String,
    value: String
}

fn parse_property<'de, D>(deserializer: D) -> Result<Property, D::Error>
where
    D: Deserializer<'de>,
{
    struct PropertyParser;
    impl<'de> Visitor<'de> for PropertyParser
    {
        type Value = Property;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("expect [key, val]")
        }
        
        fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
            println!("In custom deserializer");
            let mut prop = Property { ..Default::default() };
            
            let tmp = seq.next_element::<Key>()?;
            if let Some(a) = tmp {
                prop.id = a.value;
            };
            
            let tmp = seq.next_element::<Val>()?;
            if let Some(b) = tmp {
                prop.name = b.value;
            };
            
            Ok(prop)
        }
    }

    deserializer.deserialize_any(PropertyParser{})
}


fn main() {
    println!("Hello, world!");
    let data = r#"
        {
  "name": "customer",
  "properties": [
    {
      "name": "id",
      "type": "int",
      "value": 32
    },
    {
      "name": "name",
      "type": "string",
      "value": "John"
    }
  ]
}"#;

    let p: Customer = serde_json::from_str(data).unwrap();

    println!("Please call {} at the number {} {}", p.name, p.properties.id, p.properties.name);

}

playground

Joulin Nicolas · Accepted Answer · 2020-09-25 07:29:15Z

Thanks to edkeveked's answer I managed to find a solution that fits my needs pretty well.

Basically I rearranged the Deserializer to loop over the whole properties array and try to match every object in it with an Enum variant. I like this because I can easily map a new property in the future if it comes to it and it feels more flexible type-wise.

Anyway, here's the code for it :

extern crate serde;
extern crate serde_json;
#[macro_use]
extern crate serde_derive;

use serde::de::{Deserializer, SeqAccess, Visitor};
use std::fmt;

#[derive(Serialize, Deserialize, Debug)]
struct Customer {
    name: String,
    #[serde(deserialize_with = "parse_property")]
    properties: CustomerProps,
}

#[derive(Default, Serialize, Deserialize, Debug)]
struct CustomerProps {
    id: i32,
    name: String,
}

#[derive(Serialize, Deserialize, Debug)]
#[serde(tag = "name", content = "value")]
enum Property {
    #[serde(rename = "id")]
    Id(i32),
    #[serde(rename = "name")]
    Name(String),
}

fn parse_property<'de, D>(deserializer: D) -> Result<CustomerProps, D::Error>
where
    D: Deserializer<'de>,
{
    struct PropertyParser;
    impl<'de> Visitor<'de> for PropertyParser {
        type Value = CustomerProps;

        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
            formatter.write_str("[u64, f32, usize]")
        }

        fn visit_seq<A: SeqAccess<'de>>(self, mut seq: A) -> Result<Self::Value, A::Error> {
            let mut prop = CustomerProps {
                ..Default::default()
            };
            while let Some(tmp) = seq.next_element::<Property>()? {
                match tmp {
                    Property::Id(id) => prop.id = id,
                    Property::Name(name) => prop.name = name,
                }
            }
            Ok(prop)
        }
    }
    deserializer.deserialize_any(PropertyParser {})
}

fn main() {
    let data = r#"{
        "name": "customer",
        "properties": [
            {
                "name": "id",
                "type": "int",
                "value": 32
            },
            {
                "name": "name",
                "type": "string",
                "value": "John"
            }
        ]
    }"#;

    let p: Customer = serde_json::from_str(data).unwrap();

    println!("Please call {} at the number {} {}", p.name, p.properties.id, p.properties.name);
}

Modship · Accepted Answer · 2020-09-24 11:57:51Z

-2

I think you can use generic data types. You can find more information about that on the book

answered Sep 24, 2020 at 11:57

Modship

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