### Class

# Json Path

since: 0.14

#### Description [src]

    final class Json.Path : GObject.Object {
      /* No available fields */
    }

`JsonPath` is a simple class implementing the JSONPath syntax for extracting data out of a JSON tree.

While the semantics of the JSONPath expressions are heavily borrowed by the XPath specification for XML, the syntax follows the ECMAScript origins of JSON.

Once a `JsonPath` instance has been created, it has to compile a JSONPath expression using `json_path_compile()` before being able to match it to a JSON tree; the same `JsonPath` instance can be used to match multiple JSON trees. It it also possible to compile a new JSONPath expression using the same `JsonPath` instance; the previous expression will be discarded only if the compilation of the new expression is successful.

The simple convenience function `json_path_query()` can be used for one-off matching.

## Syntax of the JSONPath expressions

A JSONPath expression is composed by path indices and operators. Each path index can either be a member name or an element index inside a JSON tree. A JSONPath expression must start with the `$` operator; each path index is separated using either the dot notation or the bracket notation, e.g.:

    // dot notation
    $.store.book[0].title

    // bracket notation
    $['store']['book'][0]['title']

The available operators are:

- The `$` character represents the root node of the JSON tree, and matches the entire document.

- Child nodes can either be matched using `.` or `[]`. For instance, both `$.store.book` and `$['store']['book']` match the contents of the book member of the store object.

- Child nodes can be reached without specifying the whole tree structure through the recursive descent operator, or `..`. For instance, `$..author` matches all author member in every object.

- Child nodes can grouped through the wildcard operator, or `*`. For instance, `$.store.book[*].author` matches all author members of any object element contained in the book array of the store object.

- Element nodes can be accessed using their index (starting from zero) in the subscript operator `[]`. For instance, `$.store.book[0]` matches the first element of the book array of the store object.

- Subsets of element nodes can be accessed using the set notation operator `[i,j,...]`. For instance, `$.store.book[0,2]` matches the elements 0 and 2 (the first and third) of the book array of the store object.

- Slices of element nodes can be accessed using the slice notation operation `[start:end:step]`. If start is omitted, the starting index of the slice is implied to be zero; if end is omitted, the ending index of the slice is implied to be the length of the array; if step is omitted, the step of the slice is implied to be 1. For instance, `$.store.book[:2]` matches the first two elements of the book array of the store object.

More information about JSONPath is available on Stefan Gössner’s JSONPath website.

## Example of JSONPath matches

The following example shows some of the results of using `JsonPath` on a JSON tree. We use the following JSON description of a bookstore:

    { "store": {
        "book": [
          { "category": "reference", "author": "Nigel Rees",
            "title": "Sayings of the Century", "price": "8.95"  },
          { "category": "fiction", "author": "Evelyn Waugh",
            "title": "Sword of Honour", "price": "12.99" },
          { "category": "fiction", "author": "Herman Melville",
            "title": "Moby Dick", "isbn": "0-553-21311-3",
            "price": "8.99" },
          { "category": "fiction", "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings", "isbn": "0-395-19395-8",
            "price": "22.99" }
        ],
        "bicycle": { "color": "red", "price": "19.95" }
      }
    }

We can parse the JSON using `JsonParser`:

    JsonParser *parser = json_parser_new ();
    json_parser_load_from_data (parser, json_data, -1, NULL);

If we run the following code:

    JsonNode *result;
    JsonPath *path = json_path_new ();
    json_path_compile (path, "$.store..author", NULL);
    result = json_path_match (path, json_parser_get_root (parser));

The `result` node will contain an array with all values of the author member of the objects in the JSON tree. If we use a `JsonGenerator` to convert the `result` node to a string and print it:

    JsonGenerator *generator = json_generator_new ();
    json_generator_set_root (generator, result);
    char *str = json_generator_to_data (generator, NULL);
    g_print ("Results: %s\n", str);

The output will be:

    ["Nigel Rees","Evelyn Waugh","Herman Melville","J. R. R. Tolkien"]

Available since: 0.14

#### Ancestors

- GObject

#### Constructors

###### json_path_new

Creates a new `JsonPath` instance.

since: 0.14

#### Functions

###### json_path_query

Queries a JSON tree using a JSONPath expression.

since: 0.14

#### Instance methods

###### json_path_compile

Validates and decomposes the given expression.

since: 0.14

###### json_path_match

Matches the JSON tree pointed by `root` using the expression compiled into the `JsonPath`.

since: 0.14

##### Methods inherited from GObject (43)

Please see GObject for a full list of methods.

#### Signals

##### Signals inherited from GObject (1)

###### GObject::notify

The notify signal is emitted on an object when one of its properties has its value set through g_object_set_property(), g_object_set(), et al.

#### Class structure

    struct JsonPathClass {
      /* no available fields */
    }

No description available.