Expand description

Robust Rust library for flattening JSON objects

Given a JSON object it produces another one with all the nested objects and arrays flattened. The string used to separate the concatenated keys, and the way the arrays are formatted can be configured.


  • Empty arrays and objects are ignored by default, but it’s configurable.
  • The empty key "" and the JSON null value can be used without problems and are preserved.
  • Having two or more keys that end being the same after flattening the object returns an error.
  • The JSON value passed to be flattened must be an object. The object can contain any valid JSON, though.

Usage example

 use flatten_json_object::ArrayFormatting;
 use flatten_json_object::Flattener;
 use serde_json::json;

 let obj = json!({
     "a": {
         "b": [1, 2.0, "c", null, true, {}, []],
         "" : "my_key_is_empty"
     "" : "my_key_is_also_empty"
         .set_array_formatting(ArrayFormatting::Surrounded {
             start: "[".to_string(),
             end: "]".to_string()
         "a.b[0]": 1,
         "a.b[1]": 2.0,
         "a.b[2]": "c",
         "a.b[3]": null,
         "a.b[4]": true,
         "a.": "my_key_is_empty",
         "": "my_key_is_also_empty",


Basic struct of this crate. It contains the configuration. Instantiate it and use the method flatten to flatten a JSON object.


Enum to specify how arrays are formatted.

Errors that can happen while using this crate.