JSON Module
JSON (JavaScript Object Notation) is a popular data exchange format for applications written in JavaScript. This module contains XQuery functions to parse and serialize JSON documents. All functions are preceded by the json:
prefix, which is linked to the http://www.basex.org/json
namespace. The proposed JSON functions will be officially supported with the upcoming Version 6.8 of BaseX.
As there are notable differences between JSON and XML, no mapping exists that guarantees a lossless, bidirectional conversion between JSON and XML. For this reason, we offer two sets of functions in this module:
Contents
JSON
json:parse and json:serialize facilitate a lossless conversion from JSON to XML and back. The transformation is based on the following rules:
- The resulting document has a
<json/>
root node. - Names (keys) of objects are represented as elements:
- Empty names are represented by a single underscore (
<_>...</_>
). - Underscore characters are rewritten to two underscores (
__
). - A character that cannot be represented as NCName character is rewritten to an underscore and its four-digit Unicode.
- Empty names are represented by a single underscore (
- As arrays have no names, {@code <value/>} is used as element name.
- JSON values are represented as text nodes.
- The types of values are represented in attributes:
- The value types number, boolean, null, object and array are represented by a
type
attribute. - The string type is omitted, as it is treated as default type.
- If a name has the same type throughout the document, the
type
attribute will be omitted. Instead, the name will be listed in additional, type-specific attributes in the root node. The attributes are named by their type in the plural (numbers, booleans, nulls, objects and arrays), and the attribute value contains all names with that type, separated by whitespaces.
- The value types number, boolean, null, object and array are represented by a
json:parse
Signatures | json:parse($input as xs:string()) as element(json)
|
Summary | Converts the JSON document specified by $input to XML, and returns the result as element(json) instance. The converted XML document is both well readable and lossless, i.e., the converted document can be serialized back to the original JSON representation.
|
Errors | BASX0015 is raised if the specified input cannot be parsed as JSON document. |
json:serialize
Signatures | json:serialize($input as node()) as xs:string()
|
Summary | Serializes the node specified by $input as JSON, and returns the result as xs:string instance. The serialized node must conform to the syntax specified by the json:parse() function.XML documents in the JSON format can also be serialized if the Serialization Option "method" is set to "json" .
|
Errors | BASX0016 is raised if the specified node cannot be serialized as JSON document. |
Examples
Example 1: A basic example to convert an empty JSON document
Query:
json:parse('{}')
Result:
<json/>
Example 2: Conversion of some simple objects and arrays
Query:
json:parse('{ "title": "Talk On Travel Pool", "link": "http://www.flickr.com/groups/talkontravel/pool/", "description": "Travel and vacation photos from around the world.", "modified": "2009-02-02T11:10:27Z", "generator": "http://www.flickr.com/" }')
Result:
<json> <title>Talk On Travel Pool</title> <link>http://www.flickr.com/groups/talkontravel/pool/</link> <description>Travel and vacation photos from around the world.</description> <modified>2009-02-02T11:10:27Z</modified> <generator>http://www.flickr.com/</generator> </json>
Example 3: Globally defined data types, key rewritings
Query:
json:parse('{ "last_name": "John Smith", "age": 25, "address": { "street": "21 2nd Street", "city": "New York", "code": 10021 }, "phone": [ { "type": "home", "number": "212 555-1234" } ] }')
Result:
<json numbers="age code" arrays="phone" objects="json address value"> <last__name>John Smith</last__name> <age>25</age> <address> <street>21 2nd Street</street> <city>New York</city> <code>10021</code> </address> <phone> <value> <type>home</type> <number>212 555-1234</number> </value> </phone> </json>
JsonML
json:serialize-ml and json:parse-ml are used to transform XML to JSON and back, as described in the JsonML specification. JsonML can be used to transform any XML document to JSON and back. Note, however, that namespaces, comments and processing instructions will be discarded in the transformation process. More details are found in the official JsonML documentation.
json:serialize-ml
Signatures | json:serialize($input as node()) as xs:string()
|
Summary | Serializes the node specified by $input and returns the result as xs:string instance.
|
Errors | BASX0016 is raised if the specified node cannot be serialized as JSON document. |
json:parse-ml
Signatures | json:parse($input as xs:string()) as element()
|
Summary | Converts the JsonML document specified by $input to XML, and returns the result as element() instance. The JSON input must conform to the JsonML specification to be successfully converted.
|
Errors | BASX0015 is raised if the specified input cannot be parsed as JsonML instance. |
Examples
Example 1: A basic example to convert an empty XML document
Query:
json:serialize-ml(<xml/>)
Result:
["xml"]
Example 2: Conversion of some simple objects and arrays
Query:
json:serialize-ml(doc('input.xml'))
input.xml:
'''input.xml:''' <pre class="brush:xml"> <address id='1'> <last_name>Smith</last_name> <age>25</age> <address> <street>21 2nd Street</street> <city>New York</city> <code>10021</code> </address> <phone type='home'>212 555-1234</phone> </address>
Result:
["flickr", ["title", "Talk On Travel Pool"], ["link", "http:\/\/www.flickr.com\/groups\/talkontravel\/pool\/"], ["description", "Travel and vacation photos from around the world."], ["modified", "2009-02-02T11:10:27Z"], ["generator", "http:\/\/www.flickr.com\/"]]
Example 3: Nested document with attributes
Query:
json:serialize-ml(doc('input.xml'))
input.xml:
<address id='1'> <last_name>Smith</last_name> <age>25</age> <address> <street>21 2nd Street</street> <city>New York</city> <code>10021</code> </address> <phone type='home'>212 555-1234</phone> </address>
Result:
["address", {"id":"1"}, ["last_name", "Smith"], ["age", "25"], ["address", ["street", "21 2nd Street"], ["city", "New York"], ["code", "10021"]], ["phone", {"type":"home"}, "212 555-1234"]]