JSON Module
This XQuery Module contains functions to parse and serialize JSON data JSON (JavaScript Object Notation) is a popular data exchange format for applications written in JavaScript. As there are notable differences between JSON and XML, or XQuery data types, 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 and errors in this module are assigned to the http://basex.org/modules/json
namespace, which is statically bound to the json
prefix.
Conversion Formats
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.
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 encoded, as described in the Conversion Module, and used as element name.
- Array entries are also represented via elements, with
_
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.
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.
XQuery
The xquery
format is lossless, too. It converts JSON data to an XQuery value (a map, array, string, number, boolean, or empty sequence) and vice versa. The conversion rules are the same as for fn:parse-json.
The resulting representation consumes less memory than XML-based formats, and values can be directly accessed without conversion. Thus, it is recommendable for very large inputs and for efficient ad-hoc processing.
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 (see above). | direct , attributes , jsonml , xquery
|
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 |
escape
|
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
|
no Default changed with Version 10
|
serialize |
Functions
json:doc
Signature | json:doc( $href as xs:string, $options as map(*)? := map { } ) as item()? |
Summary | Fetches the JSON document referred to by the given $href and converts it to an XQuery value. The $options argument can be used to control the way the input is converted.
|
Errors | parse : the specified input cannot be parsed as JSON document.options : the specified options are conflicting.
|
json:parse
Signature | json:parse( $value as xs:string?, $options as map(*)? := map { } ) as item()? |
Summary | Converts the JSON $value to an XQuery value. 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 | parse : the specified input cannot be parsed as JSON document.options : the specified options are conflicting.
|
json:serialize
Signature | json:serialize( $input as item()? $options as map(*)? := map { } ) as xs:string |
Summary | Serializes the specified $input as JSON, using the specified $options , and returns the result as string:
Values can also be serialized as JSON with the standard Serialization feature of XQuery:
|
Errors | serialize : 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: <syntaxhighlight lang="xquery"> 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) </syntaxhighlight>
Example 2: Converts a simple JSON string to XML and back
Query: <syntaxhighlight lang="xquery"> json:parse('{}') </syntaxhighlight>
Result: <syntaxhighlight lang="xml"> <json type="object"/> </syntaxhighlight>
Query: <syntaxhighlight lang="xquery"> (: serialize result as plain text :) declare option output:method 'text'; json:serialize(<json type="object"/>) </syntaxhighlight>
Result: <syntaxhighlight lang="xquery"> { } </syntaxhighlight>
Example 3: Converts a JSON string with simple objects and arrays
Query: <syntaxhighlight lang="xquery"> 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/"
}') </syntaxhighlight>
Result: <syntaxhighlight lang="xml"> <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> </syntaxhighlight>
Example 4: Converts a JSON string with different data types
Query: <syntaxhighlight lang="xquery"> 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) </syntaxhighlight>
Result: <syntaxhighlight lang="xml"> <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>
10021
</address>
<phone>
<_>
<type>home</type>
<number>212 555-1234</number>
</_>
<_>
<type>mobile</type>
<number type="number">1327724623</number>
</_>
</phone>
</json> </syntaxhighlight>
JsonML Format
Example 1: Converts all XML documents in a database to the JsonML format and writes them to disk
Query: <syntaxhighlight lang="xquery"> for $doc in collection('json') let $name := document-uri($doc) let $json := json:serialize($doc, map { 'format': 'jsonml' }) return file:write($name, $json) </syntaxhighlight>
Example 2: Converts an XML document with elements and text
Query: <syntaxhighlight lang="xquery"> json:serialize(doc('flickr.xml'), map { 'format': 'jsonml' }) </syntaxhighlight>
flickr.xml: <syntaxhighlight lang="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> </syntaxhighlight>
Result: <syntaxhighlight lang="json"> ["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/"]]
</syntaxhighlight>
Example 3: Converts a document with nested elements and attributes to JsonML
Query: <syntaxhighlight lang="xquery"> json:serialize(doc('input.xml'), map { 'format': 'jsonml' }) </syntaxhighlight>
input.xml: <syntaxhighlight lang="xml"> <address id='1'>
<last_name>Smith</last_name>
<age>25</age>
<address xmlns='will be dropped as well'>
<street>21 2nd Street</street>
<city>New York</city>
10021
</address>
<phone type='home'>212 555-1234</phone>
</address> </syntaxhighlight>
Result: <syntaxhighlight lang="json"> ["address", {"id":"1"},
["last_name", "Smith"], ["age", "25"], ["address", ["street", "21 2nd Street"], ["city", "New York"], ["code", "10021"]], ["phone", {"type":"home"}, "212 555-1234"]]
</syntaxhighlight>
XQuery Format
Example 1: Converts a JSON string to XQuery
Query: <syntaxhighlight lang="xquery"> let $input := '{
"Title": "Drinks", "Author": [ "Jim Daniels", "Jack Beam" ]
}' let $data := json:parse($input, map { 'format': 'xquery' }) return map:for-each($data, function($k, $v) {
$k || ': ' || string-join($v, ', ')
}) </syntaxhighlight>
Result: <syntaxhighlight lang="json"> Author: Jim Daniels, Jack Beam Title: Drinks </syntaxhighlight>
Example 2: Converts XQuery data to JSON
Query: <syntaxhighlight lang="xquery"> for $item in (
true(), 'ABC', array { 1 to 5 }, map { "Key": "Value" }
) return json:serialize(
$item, map { 'format': 'xquery', 'indent': 'no' }
) </syntaxhighlight>
Result: <syntaxhighlight lang="json"> true "ABC" [1,2,3,4,5] {"Key":"Value"} </syntaxhighlight>
Errors
Code | Description |
---|---|
options
|
The specified options are conflicting. |
parse
|
The specified input cannot be parsed as JSON document. |
serialize
|
The specified node cannot be serialized as JSON document. |
Changelog
- Version 10.0
- Updated:
indent
: Default changed fromyes
tono
.
- Version 9.4
- Added:
json:doc
- Version 9.1
- Updated:
json:parse
can be called with empty sequence.
- Version 9.0
- Updated:
map
format renamed toxquery
. - Updated: error codes updated; errors now use the module namespace
- Version 8.4
- Updated:
unescape
changed toescape
.
- 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 tojson:parse
andjson:serialize
. - Updated:
json:parse-ml
andjson:serialize-ml
are now deprecated.
The module was introduced with Version 7.0.