JSON Module
This XQuery Module contains functions to parse and serialize JSON documents. JSON (JavaScript Object Notation) is a popular data exchange format for applications written in JavaScript. 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 various mappings, all of which are suited to different use cases.
Contents
Conventions
All functions in this module are assigned to the http://basex.org/modules/json
namespace, which is statically bound to the json
prefix.
All errors are assigned to the http://basex.org/errors
namespace, which is statically bound to the bxerr
prefix.
Conversion Formats
Direct
The direct
conversion format allows 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. - Object pairs are represented via elements. The name of a pair is rewritten to an element name:
- Empty names are represented by a single underscore (
_
). Existing underscores are rewritten to two underscores (__
), and characters that are not valid in element names are rewritten to an underscore and the character’s four-digit Unicode. - If the
lax
option is set totrue
, invalid characters are simply replaced with underscores or (when invalid as first character of an element name) prefixed with an underscore. The resulting names are better readable, but cannot always be converted back to their original form.
- Empty names are represented by a single underscore (
- Array entries are also represented via elements.
_
is used as element name. - Object and array values are stored in text nodes.
- The types of values are represented via
type
attributes:- The existing types are string, number, boolean, null, object, and array.
- As most values are strings, the string type is by default omitted.
Attributes
The attributes
format is lossless, too. The transformation based on the following rules:
- The resulting document has a
<json>
root node. - Object pairs are represented via
<pair>
elements. The name of a pair is stored in aname
attribute. - Array entries are represented via
<item>
elements. - Object and array values are stored in text nodes.
- The types of values are represented via
type
attributes:- The existing types are string, number, boolean, null, object, and array.
- As most values are strings, the string type is by default omitted.
Map
The map
format is lossless, too. It converts a JSON document to an XQuery map and vice versa. The conversion rules are the same as for fn:parse-json.
Basic
The basic
format is another lossless format. It converts a JSON document to an XML node and vice versa. The conversion rules are the same as for fn:json-to-xml.
JsonML
The jsonml
format is designed to convert XML to JSON and back, using the JsonML dialect. JsonML allows the transformation of arbitrary XML documents, but namespaces, comments and processing instructions will be discarded in the transformation process. More details are found in the official JsonML documentation.
A little advice: in the Database Creation dialog of the GUI, if you select JSON Parsing and switch to the Parsing tab, you can see the effects of some of the conversion options.
Options
The following options are available (the Direction column indicates if an option applies to parsing, serialization, or both operations):
Option | Description | Allowed | Default | Direction |
---|---|---|---|---|
format
|
Specifies the format for converting JSON data. | direct , attributes , jsonml , map
|
direct
|
parse, serialize |
liberal
|
Determines if minor deviations from RFC 7159 will be ignored. | yes , no
|
no
|
parse |
merge
|
This option is considered when direct or attributes conversion is used:
|
yes , no
|
no
|
parse, serialize |
strings
|
Indicates if type attributes will be added for strings.
|
yes , no
|
yes
|
parse, serialize |
lax
|
Specifies if a lax approach is used to convert QNames to JSON names. | yes , no
|
no
|
parse, serialize |
unescape
|
Indicates if escaped characters are expanded (for example, \n becomes a single x0A character, while \u20AC becomes the character € ).
|
yes , no
|
yes
|
parse |
escape
|
Indicates if characters are escaped whenever the JSON syntax requires it. This option can be set to no if strings are already in escaped form and no further escaping is permitted.
|
yes , no
|
yes
|
serialize |
indent
|
Indicates if whitespace should be added to the output with the aim of improving human legibility. If the parameter is set as in the query prolog, it overrides the indent serialization parameter.
|
yes , no
|
yes
|
serialize |
Functions
json:parse
Signatures | json:parse($input as xs:string) as element(json) json:parse($input as xs:string, $options as map(xs:string, xs:string)) as item()
|
Summary | Converts the JSON document specified by $input to an XML document or a map. If the input can be successfully parsed, it can be serialized back to the original JSON representation. The $options argument can be used to control the way the input is converted.
|
Errors | BXJS0001 : the specified input cannot be parsed as JSON document.
|
json:serialize
Signatures | json:serialize($input as node()) as xs:string json:serialize($input as node(), $options as map(xs:string, xs:string)) as xs:string
|
Summary | Serializes the node specified by $input as JSON, and returns the result as xs:string instance. The node is expected to conform to the output created by the json:parse() function. All other items will be serialized as specified for the json output method of the official specification.Items can also be serialized as JSON if the Serialization Parameter method is set to json .The $options argument can be used to control the way the input is serialized.
|
Errors | BXJS0002 : the specified node cannot be serialized as JSON document.
|
Examples
BaseX Format
Example 1: Adds all JSON documents in a directory to a database
Query:
let $database := "database" for $name in file:list('.', false(), '*.json') let $file := file:read-text($name) let $json := json:parse($file) return db:add($database, $json, $name)
Example 2: Converts a simple JSON string to XML and back
Query:
json:parse('{}')
Result:
<json type="object"/>
Query:
(: serialize result as plain text :) declare option output:method 'text'; json:serialize(<json type="object"/>)
Result:
{ }
Example 3: Converts a JSON string with 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": "2014-02-02T11:10:27Z", "generator": "http://www.flickr.com/" }')
Result:
<json type="object"> <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>2014-02-02T11:10:27Z</modified> <generator>http://www.flickr.com/</generator> </json>
Example 4: Converts a JSON string with different data types
Query:
let $options := map { 'merge': true() } return json:parse('{ "first_name": "John", "last_name": "Smith", "age": 25, "address": { "street": "21 2nd Street", "city": "New York", "code": 10021 }, "phone": [ { "type": "home", "number": "212 555-1234" }, { "type": "mobile", "number": 1327724623 } ] }', $options)
Result:
<json numbers="age code" arrays="phone" objects="json address value"> <first__name>John</first__name> <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</type> <number>212 555-1234</number> </_> <_> <type>mobile</type> <number type="number">1327724623</number> </_> </phone> </json>
JsonML Format
Example 1: Converts all XML documents in a database to JsonML and writes them to disk
Query:
for $doc in collection('json') let $name := document-uri($doc) let $json := json:serialize($doc) return file:write($name, $json)
Example 2: Converts a simple XML fragment to the JsonML format
Query:
json:serialize(<xml/>, map { 'format': 'jsonml' })
Result:
["xml"]
Example 3: Converts an XML document with elements and text
Query:
json:serialize(doc('flickr.xml'), map { 'format': 'jsonml' })
flickr.xml:
<flickr> <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>2014-02-02T11:10:27Z</modified> <generator>http://www.flickr.com/</generator> </flickr>
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", "2014-02-02T11:10:27Z"], ["generator", "http://www.flickr.com/"]]
Example 4: Converts a document with nested elements and attributes
Query:
json:serialize(doc('input.xml'), map { 'format': 'jsonml' })
input.xml:
<address id='1'> <!-- comments will be discarded --> <last_name>Smith</last_name> <age>25</age> <address xmlns='will be dropped as well'> <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"]]
Errors
Code | Description |
---|---|
BXJS0001
|
The specified input cannot be parsed as JSON document. |
BXJS0002
|
The specified node cannot be serialized as JSON document. |
Changelog
- Version 8.2
- Added: Conversion format
basic
.
- Version 8.0
- Updated: Serialization aligned with the
json
output method of the official specification. - Added:
liberal
option. - Removed:
spec
option.
- Version 7.8
- Removed:
json:parse-ml
,json:serialize-ml
. - Updated:
json:parse
now returns a document node instead of an element, or an XQuery map ifformat
is set to.map
.
- Version 7.7.2
- Updated:
$options
argument added to json:parse and json:serialize. - Updated: json:parse-ml and json:serialize-ml are now deprecated.
The module was introduced with Version 7.0.