lxh023 / jsonpath

JSONPath (XPath-like syntax for JSON) C# implementation

JSONPath

This project is a C# implementation of JSONPath.

JSONPath Expressions

Portions © 2006 Stefan Gössner

JSONPath expressions always refer to a JSON structure in the same way as XPath expression are used in combination with an XML document. Since a JSON structure is usually anonymous and doesn't necessarily have a root member object JSONPath assumes the abstract name $ assigned to the outer level object.

JSONPath expressions can use the dot-notation:

$.store.book[0].title

or the bracket-notation:

$['store']['book'][0]['title']

for input paths. Internal or output paths will always be converted to the more general bracket-notation.

JSONPath allows the wildcard symbol * for member names and array indices. It borrows the descendant operator .. from E4X and the array slice syntax proposal [start:end:step] from ECMASCRIPT 4.

Expressions of the underlying scripting language (<expr>) can be used as an alternative to explicit names or indices, as in:

$.store.book[(@.length-1)].title

using the symbol @ for the current object. Filter expressions are supported via the syntax ?(<boolean expr>), as in:

$.store.book[?(@.price < 10)].title

Below is a complete overview and a side-by-side comparison of the JSONPath syntax elements with its XPath counterparts:

XPath	JSONPath	Description
/	$	The root object/element
.	@	The current object/element
/	. or []	Child operator
..	n/a	Parent operator
//	..	Recursive descent. JSONPath borrows this syntax from E4X.
*	*	Wildcard. All objects/elements regardless their names.
@	n/a	Attribute access. JSON structures don't have attributes.
[]	[]	Subscript operator. XPath uses it to iterate over element collections and for predicates. In Javascript and JSON it is the native array operator.
|	[,]	Union operator in XPath results in a combination of node sets. JSONPath allows alternate names or array indices as a set.
n/a	[start:end:step]	Array slice operator borrowed from ES4.
[]	?()	Applies a filter (script) expression.
n/a	()	Script expression, using the underlying script engine.
()	n/a	Grouping in XPath

Examples

Portions © 2006 Stefan Gössner

Let's practice JSONPath expressions by some more examples. We start with a simple JSON structure built after an XML example representing 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
    }
  }
}

XPath	JSONPath	Result	Notes
/store/book/author	$.store.book[*].author	The authors of all books in the store
//author	$..author	All authors
/store/*	$.store.*	All things in store, which are some books and a red bicycle
/store//price	$.store..price	The price of everything in the store
//book[3]	$..book[2]	The third book
//book[last()]	$..book[(@.length-1)]<br>$..book[-1:]	The last book in order
//book[position()<3]	$..book[0,1] $..book[:2]	The first two books
`//book/*[self::category	self::author]or//book/(category,author)` in XPath 2.0	$..book[category,author]	The categories and authors of all books
//book[isbn]	$..book[?(@.isbn)]	Filter all books with isbn number
//book[price<10]	$..book[?(@.price<10)]	Filter all books cheapier than 10
//*[price>19]/..	$..[?(@.price>19)]	Categories with things more expensive than 19	Parent (caret) not present in original spec
//*	$..*	All elements in XML document; all members of JSON structure
/store/book/[position()!=1]	$.store.book[?(@path !== "$[\'store\'][\'book\'][0]")]	All books besides that at the path pointing to the first	@path not present in original spec