JMESPath Community is the community implementation of JMESPath, a query and transformation language for JSON.

Evaluating JMESPath Expression

Use the search function to evaluate a JMESPath expression.

Example

use jmespath_community as jmespath;
use jmespath::{search, Value};

// Parse some JSON data into a JMESPath variable
let json_str = "{\"foo\":{\"bar\":{\"baz\":true}}}";
let data = Value::from_json(json_str).unwrap();

let result = search("foo.bar | baz", &data).unwrap();
assert_eq!(true, result);

A JMESPath expression can be parsed once and evaluated multiple times using the parse function.

Example

use jmespath_community as jmespath;
use jmespath::{parse, Value};

let ast = parse("foo").unwrap();
let data = Value::from_json(r#"{"foo": "bar"}"#).unwrap();
let result = ast.search(&data).unwrap();
assert_eq!("bar", result);

Registering Custom Functions

JMESPath Community comes with a host of useful builtin functions. However, it can be extended with third-party functions.

Example

mod custom_functions {

use jmespath_community as jmespath;

use jmespath::function;

use jmespath::errors::Error as RuntimeError;

use jmespath::FunctionContext;
use jmespath::Value;

use jmespath::functions::ReturnValue;
use jmespath::functions::Function;

use jmespath::functions::DataType;
use jmespath::functions::ParamTypes::*;
use jmespath::functions::Parameter;
use jmespath::functions::Parameter::*;

function!(
add,
[
left => Required(Of(DataType::Number)),
right => Required(Of(DataType::Number))
],
arguments,
{
// type checking has been performed by the runtime
// safe to unwrap

let i = arguments[0].as_f64().unwrap();
let j = arguments[1].as_f64().unwrap();

Value::from_f64(i + j)
}
);
}

Create a new instance of the JMESPath Runtime object and register your custom function:

Example

use jmespath_community as jmespath;
use jmespath::FunctionRegistrar;
use jmespath::{Runtime, Value};

let add = Box::new(custom_functions::add::new());
let mut runtime = Runtime::create_runtime();
runtime.register(add);

let expression = "foo";
let root = Value::Null;
let result = runtime.search(expression, &root).unwrap();

assert_eq!(None, result);