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.:

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

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

The available operators are:

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:

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{ "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:

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

If we run the following code:

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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 JsonNode 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 JsonNode to a string and print it:

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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:

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

JsonPath is available since JSON-GLib 0.14

json_path_new ()

JsonPath *
json_path_new (void);

Creates a new JsonPath instance.

Once created, the JsonPath object should be used with json_path_compile() and json_path_match().

Since 0.14

JSON_PATH_ERROR

#define JSON_PATH_ERROR         (json_path_error_quark ())

Error domain for JsonPath errors

Since 0.14

json_path_compile ()

gboolean
json_path_compile (JsonPath *path,
                   const char *expression,
                   GError **error);

Validates and decomposes expression .

A JSONPath expression must be compiled before calling json_path_match().

Since 0.14

json_path_match ()

JsonNode *
json_path_match (JsonPath *path,
                 JsonNode *root);

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

The matching JsonNodes will be copied into a JsonArray and returned wrapped in a JsonNode.

Since 0.14

json_path_query ()

JsonNode *
json_path_query (const char *expression,
                 JsonNode *root,
                 GError **error);

Queries a JSON tree using a JSONPath expression.

This function is a simple wrapper around json_path_new(), json_path_compile() and json_path_match(). It implicitly creates a JsonPath instance, compiles expression and matches it against the JSON tree pointed by root .

Since 0.14

JsonPath

typedef struct _JsonPath JsonPath;

The JsonPath structure is an opaque object whose members cannot be directly accessed except through the provided API.

Since 0.14

JsonPathClass

typedef struct _JsonPathClass JsonPathClass;

The JsonPathClass structure is an opaque object class whose members cannot be directly accessed.

Since 0.14

enum JsonPathError

Error code enumeration for the JSON_PATH_ERROR domain.

Since 0.14