#json #extract #macro #property #variant #nested #boilerplate

json_extract

This macro reduces boilerplate when using serde_json::Value variants when trying to get into a nested property

1 unstable release

Uses new Rust 2021

0.1.4 Mar 24, 2022
0.1.3 Mar 24, 2022
0.1.2 Mar 23, 2022
0.1.1 Mar 23, 2022
0.1.0 Mar 23, 2022

#676 in Rust patterns

28 downloads per month

MIT license

9KB
57 lines

json-extract-macro

Access nested JSON values in 1 line of code

This macro reduces boilerplate when using serde_json::Value variants when trying to get into a nested property.

let json_parsed = serde_json::json!({
   "brand": {
      "tesla": {
         "model": {
             "designers": "Mr Bean"
            }
         }
     }
 });

let designer: Option<String> = json_extract!("brand.tesla.model.designer", &json_parsed, String);

println!("Who tf is this designer? {}",designer.unwrap_or_default());

or...

 if let serde_json::Value::Object(brand) = &json_parsed {
     let brand = brand.get("brand").unwrap();
     if let serde_json::Value::Object(tesla) = &brand {
         let tesla = tesla.get("tesla").unwrap();
         if let serde_json::Value::Object(model) = &tesla {
             let model = model.get("model").unwrap();
             if let serde_json::Value::Object(designers) = &model {
                 let res = designer.get("designer");
                 let designer = serde_json::from_value::<String>(res.unwrap().to_owned()).unwrap();
             }
         }
     }
 }

println!("Who tf is this designer? {}",designer.unwrap_or_default());

Macro args

The macro accepts 3 arguments:

  1. A &str containg the path, separated by "."
  2. The serde_json::Value variable to read.
  3. The type of the property we want to get.

Types supported

json_serde::Value has the following variants:

  • Array
  • Bool
  • Null
  • Number
  • Object
  • String

The third parameter to pass in the macro is a Rust type, so, things we can pass if we want to get data from some variants:

Value variant Rust types
Array Vec<String>, Vec<bool>, Vec<f64>, Vec<Value> ...
Bool bool
Number u32, i32, i64, f32, usize ...
Object Value
String String
Null not supported

Dependencies

~0.6–1.3MB
~30K SLoC