Difference between revisions of "JSON Module"
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− | This [[Module Library|XQuery Module]] contains functions to parse and serialize JSON | + | This [[Module Library|XQuery Module]] contains functions to parse and serialize JSON data [https://www.json.org/ 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. |
=Conventions= | =Conventions= | ||
− | All functions in this module are assigned to the | + | All functions and errors in this module are assigned to the <code><nowiki>http://basex.org/modules/json</nowiki></code> namespace, which is statically bound to the {{Code|json}} prefix.<br/> |
− | |||
− | = | + | ==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 {{Code|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 {{Code|json}} root node. | |
− | + | * Object pairs are represented via elements. The name of a pair is encoded, as described in the [[Conversion Module#Keys|Conversion Module]], and used as element name. | |
− | + | * Array entries are also represented via elements, with {{Code|_}} as element name. | |
− | + | * Object and array values are stored in text nodes. | |
− | # | + | * The types of values are represented via {{Code|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 {{Code|attributes}} format is lossless, too. The transformation based on the following rules: | ||
+ | |||
+ | * The resulting document has a {{Code|json}} root node. | ||
+ | * Object pairs are represented via {{Code|pair}} elements. The name of a pair is stored in a {{Code|name}} attribute. | ||
+ | * Array entries are represented via {{Code|item}} elements. | ||
+ | * Object and array values are stored in text nodes. | ||
+ | * The types of values are represented via {{Code|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 {{Code|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 [[XQuery 3.1#fn:json-to-xml|fn:json-to-xml]]. | ||
+ | |||
+ | ===JsonML=== | ||
+ | |||
+ | The {{Code|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 [http://jsonml.org/XML JsonML documentation]. | ||
+ | |||
+ | ===XQuery=== | ||
+ | |||
+ | The {{Code|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 [[XQuery 3.1#fn:parse-json|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): | ||
+ | |||
+ | {| class="wikitable sortable" width="100%" | ||
+ | |- valign="top" | ||
+ | ! width="140" | Option | ||
+ | ! width="50%" | Description | ||
+ | ! Allowed | ||
+ | ! Default | ||
+ | ! Direction | ||
+ | |- valign="top" | ||
+ | | {{Code|format}} | ||
+ | | Specifies the format for converting JSON data. | ||
+ | | {{Code|direct}}, {{Code|attributes}}, {{Code|jsonml}}, {{Code|xquery}} | ||
+ | | {{Code|direct}} | ||
+ | | ''parse'', ''serialize'' | ||
+ | |- valign="top" | ||
+ | | {{Code|liberal}} | ||
+ | | Determines if minor deviations from [https://www.rfc-editor.org/rfc/rfc7159.txt RFC 7159] will be ignored. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|no}} | ||
+ | | ''parse'' | ||
+ | |- valign="top" | ||
+ | | {{Code|merge}} | ||
+ | | This option is considered when {{Code|direct}} or {{Code|attributes}} conversion is used:<br/> | ||
+ | * If a name has the same type throughout the data, the {{Code|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 plural (''numbers'', ''booleans'', ''nulls'', ''objects'' and ''arrays''), and the attribute value contains all names with that type, separated by whitespaces. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|no}} | ||
+ | | ''parse'', ''serialize'' | ||
+ | |- valign="top" | ||
+ | | {{Code|strings}} | ||
+ | | Indicates if {{Code|type}} attributes will be added for strings. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|yes}} | ||
+ | | ''parse'', ''serialize'' | ||
+ | |- valign="top" | ||
+ | | {{Code|lax}} | ||
+ | | Specifies if a lax approach is used to convert QNames to JSON names. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|no}} | ||
+ | | ''parse'', ''serialize'' | ||
+ | |- valign="top" | ||
+ | | {{Code|escape}} | ||
+ | | Indicates if escaped characters are expanded (for example, {{Code|\n}} becomes a single {{Code|x0A}} character, while {{Code|\u20AC}} becomes the character {{Code|€}}). | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|yes}} | ||
+ | | ''parse'' | ||
+ | |- valign="top" | ||
+ | | {{Code|escape}} | ||
+ | | Indicates if characters are escaped whenever the JSON syntax requires it. This option can be set to {{Code|no}} if strings are already in escaped form and no further escaping is permitted. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|yes}} | ||
+ | | ''serialize'' | ||
+ | |- valign="top" | ||
+ | | {{Code|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 {{Code|indent}} [[Serialization|serialization parameter]]. | ||
+ | | {{Code|yes}}, {{Code|no}} | ||
+ | | {{Code|yes}} | ||
+ | | ''serialize'' | ||
+ | |} | ||
+ | |||
+ | =Functions= | ||
==json:parse== | ==json:parse== | ||
− | {{ | + | {| width='100%' |
+ | |- | ||
+ | | width='120' | '''Signatures''' | ||
+ | |{{Func|json:parse|$string as xs:string?|item()?}}<br/>{{Func|json:parse|$string as xs:string?, $options as map(*)?|item()?}} | ||
+ | |- | ||
+ | | '''Summary''' | ||
+ | |Converts the JSON {{Code|$string}} to an XQuery value. If the input can be successfully parsed, it can be serialized back to the original JSON representation. The {{Code|$options}} argument can be used to control the way the input is converted. | ||
+ | |- | ||
+ | | '''Errors''' | ||
+ | |{{Error|parse|#Errors}} the specified input cannot be parsed as JSON document.<br/>{{Error|options|#Errors}} the specified options are conflicting. | ||
+ | |} | ||
+ | |||
+ | ==json:doc== | ||
+ | |||
+ | {{Mark|Introduced with BaseX 9.4:}} | ||
{| width='100%' | {| width='100%' | ||
|- | |- | ||
| width='120' | '''Signatures''' | | width='120' | '''Signatures''' | ||
− | |{{Func|json: | + | |{{Func|json:doc|$uri as xs:string|item()?}}<br />{{Func|json:doc|$uri as xs:string, $options as map(*)?|item()?}}<br /> |
|- | |- | ||
| '''Summary''' | | '''Summary''' | ||
− | | | + | |Fetches the JSON document referred to by the given {{Code|$uri}} and converts it to an XQuery value. The {{Code|$options}} argument can be used to control the way the input is converted. |
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
|- | |- | ||
| '''Errors''' | | '''Errors''' | ||
− | |{{Error| | + | |{{Error|parse|#Errors}} the specified input cannot be parsed as JSON document.<br/>{{Error|options|#Errors}} the specified options are conflicting. |
|} | |} | ||
==json:serialize== | ==json:serialize== | ||
− | |||
− | |||
{| width='100%' | {| width='100%' | ||
|- | |- | ||
| width='120' | '''Signatures''' | | width='120' | '''Signatures''' | ||
− | |{{Func|json:serialize|$input as | + | |{{Func|json:serialize|$input as item()?|xs:string}}<br/>{{Func|json:serialize|$input as item()?, $options as map(*)?|xs:string}} |
|- | |- | ||
| '''Summary''' | | '''Summary''' | ||
− | |Serializes the | + | |Serializes the specified {{Code|$input}} as JSON, using the specified {{Code|$options}}, and returns the result as string: |
− | * {{Code| | + | * The input is expected to conform to the results that are created by [[#json:parse|json:parse()]]. |
− | * | + | * Non-conforming items will be serialized as specified in the [[XQuery 3.1#JSON Serialization|json output method]] of the official recommendation. |
− | + | Values can also be serialized as JSON with the standard [[Serialization]] feature of XQuery: | |
− | + | * The parameter {{Code|method}} needs to be set to {{Code|json}}, and | |
− | + | * the options presented in this article need to be assigned to the {{Code|json}} parameter. | |
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
|- | |- | ||
| '''Errors''' | | '''Errors''' | ||
− | |{{Error| | + | |{{Error|serialize|#Errors}} the specified node cannot be serialized as JSON document. |
|} | |} | ||
− | == | + | =Examples= |
+ | |||
+ | ==BaseX Format== | ||
'''Example 1: Adds all JSON documents in a directory to a database''' | '''Example 1: Adds all JSON documents in a directory to a database''' | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
let $database := "database" | let $database := "database" | ||
for $name in file:list('.', false(), '*.json') | for $name in file:list('.', false(), '*.json') | ||
let $file := file:read-text($name) | let $file := file:read-text($name) | ||
let $json := json:parse($file) | let $json := json:parse($file) | ||
− | return db:add($database, | + | return db:add($database, $json, $name) |
− | </ | + | </syntaxhighlight> |
'''Example 2: Converts a simple JSON string to XML and back''' | '''Example 2: Converts a simple JSON string to XML and back''' | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
json:parse('{}') | json:parse('{}') | ||
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="xml"> |
− | <json | + | <json type="object"/> |
− | </ | + | </syntaxhighlight> |
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
(: serialize result as plain text :) | (: serialize result as plain text :) | ||
declare option output:method 'text'; | declare option output:method 'text'; | ||
− | json:serialize(<json | + | json:serialize(<json type="object"/>) |
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
{ } | { } | ||
− | </ | + | </syntaxhighlight> |
'''Example 3: Converts a JSON string with simple objects and arrays''' | '''Example 3: Converts a JSON string with simple objects and arrays''' | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
json:parse('{ | json:parse('{ | ||
"title": "Talk On Travel Pool", | "title": "Talk On Travel Pool", | ||
"link": "http://www.flickr.com/groups/talkontravel/pool/", | "link": "http://www.flickr.com/groups/talkontravel/pool/", | ||
"description": "Travel and vacation photos from around the world.", | "description": "Travel and vacation photos from around the world.", | ||
− | "modified": " | + | "modified": "2014-02-02T11:10:27Z", |
"generator": "http://www.flickr.com/" | "generator": "http://www.flickr.com/" | ||
}') | }') | ||
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="xml"> |
− | <json | + | <json type="object"> |
<title>Talk On Travel Pool</title> | <title>Talk On Travel Pool</title> | ||
<link>http://www.flickr.com/groups/talkontravel/pool/</link> | <link>http://www.flickr.com/groups/talkontravel/pool/</link> | ||
<description>Travel and vacation photos from around the world.</description> | <description>Travel and vacation photos from around the world.</description> | ||
− | <modified> | + | <modified>2014-02-02T11:10:27Z</modified> |
<generator>http://www.flickr.com/</generator> | <generator>http://www.flickr.com/</generator> | ||
</json> | </json> | ||
− | </ | + | </syntaxhighlight> |
'''Example 4: Converts a JSON string with different data types''' | '''Example 4: Converts a JSON string with different data types''' | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
− | json:parse('{ | + | let $options := map { 'merge': true() } |
+ | return json:parse('{ | ||
"first_name": "John", | "first_name": "John", | ||
"last_name": "Smith", | "last_name": "Smith", | ||
Line 167: | Line 248: | ||
} | } | ||
] | ] | ||
− | }') | + | }', $options) |
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="xml"> |
<json numbers="age code" arrays="phone" objects="json address value"> | <json numbers="age code" arrays="phone" objects="json address value"> | ||
<first__name>John</first__name> | <first__name>John</first__name> | ||
Line 182: | Line 263: | ||
</address> | </address> | ||
<phone> | <phone> | ||
− | < | + | <_> |
<type>home</type> | <type>home</type> | ||
<number>212 555-1234</number> | <number>212 555-1234</number> | ||
− | </ | + | </_> |
− | < | + | <_> |
<type>mobile</type> | <type>mobile</type> | ||
<number type="number">1327724623</number> | <number type="number">1327724623</number> | ||
− | </ | + | </_> |
</phone> | </phone> | ||
</json> | </json> | ||
− | </ | + | </syntaxhighlight> |
− | =JsonML | + | ==JsonML Format== |
− | + | '''Example 1: Converts all XML documents in a database to the JsonML format and writes them to disk''' | |
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− | '''Example 1: Converts all XML documents in a database to JsonML and writes them to disk''' | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
for $doc in collection('json') | for $doc in collection('json') | ||
let $name := document-uri($doc) | let $name := document-uri($doc) | ||
− | let $json := json:serialize($doc) | + | let $json := json:serialize($doc, map { 'format': 'jsonml' }) |
return file:write($name, $json) | return file:write($name, $json) | ||
− | </ | + | </syntaxhighlight> |
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | + | '''Example 2: Converts an XML document with elements and text''' | |
− | |||
− | |||
− | |||
− | |||
− | '''Example | ||
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
− | json:serialize(doc('flickr.xml'), { 'format': 'jsonml' }) | + | json:serialize(doc('flickr.xml'), map { 'format': 'jsonml' }) |
− | </ | + | </syntaxhighlight> |
'''flickr.xml:''' | '''flickr.xml:''' | ||
− | < | + | <syntaxhighlight lang="xml"> |
<flickr> | <flickr> | ||
<title>Talk On Travel Pool</title> | <title>Talk On Travel Pool</title> | ||
<link>http://www.flickr.com/groups/talkontravel/pool/</link> | <link>http://www.flickr.com/groups/talkontravel/pool/</link> | ||
<description>Travel and vacation photos from around the world.</description> | <description>Travel and vacation photos from around the world.</description> | ||
− | <modified> | + | <modified>2014-02-02T11:10:27Z</modified> |
<generator>http://www.flickr.com/</generator> | <generator>http://www.flickr.com/</generator> | ||
</flickr> | </flickr> | ||
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="json"> |
["flickr", | ["flickr", | ||
["title", | ["title", | ||
"Talk On Travel Pool"], | "Talk On Travel Pool"], | ||
["link", | ["link", | ||
− | "http: | + | "http://www.flickr.com/groups/talkontravel/pool/"], |
["description", | ["description", | ||
"Travel and vacation photos from around the world."], | "Travel and vacation photos from around the world."], | ||
["modified", | ["modified", | ||
− | " | + | "2014-02-02T11:10:27Z"], |
["generator", | ["generator", | ||
− | "http: | + | "http://www.flickr.com/"]] |
− | </ | + | </syntaxhighlight> |
− | '''Example | + | '''Example 3: Converts a document with nested elements and attributes to JsonML''' |
'''Query:''' | '''Query:''' | ||
− | < | + | <syntaxhighlight lang="xquery"> |
− | json:serialize(doc('input.xml'), { 'format': 'jsonml' }) | + | json:serialize(doc('input.xml'), map { 'format': 'jsonml' }) |
− | </ | + | </syntaxhighlight> |
'''input.xml:''' | '''input.xml:''' | ||
− | < | + | <syntaxhighlight lang="xml"> |
<address id='1'> | <address id='1'> | ||
<!-- comments will be discarded --> | <!-- comments will be discarded --> | ||
Line 303: | Line 340: | ||
<phone type='home'>212 555-1234</phone> | <phone type='home'>212 555-1234</phone> | ||
</address> | </address> | ||
− | </ | + | </syntaxhighlight> |
'''Result:''' | '''Result:''' | ||
− | < | + | <syntaxhighlight lang="json"> |
["address", {"id":"1"}, | ["address", {"id":"1"}, | ||
["last_name", | ["last_name", | ||
Line 321: | Line 358: | ||
["phone", {"type":"home"}, | ["phone", {"type":"home"}, | ||
"212 555-1234"]] | "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( | ||
+ | $item, | ||
+ | map { 'format': 'xquery', 'indent': 'no' } | ||
+ | ) | ||
+ | </syntaxhighlight> | ||
+ | |||
+ | '''Result:''' | ||
+ | <syntaxhighlight lang="json"> | ||
+ | true | ||
+ | "ABC" | ||
+ | [1,2,3,4,5] | ||
+ | {"Key":"Value"} | ||
+ | </syntaxhighlight> | ||
=Errors= | =Errors= | ||
Line 329: | Line 412: | ||
|Description | |Description | ||
|- | |- | ||
− | |{{Code| | + | |{{Code|options}} |
+ | |The specified options are conflicting. | ||
+ | |- | ||
+ | |{{Code|parse}} | ||
|The specified input cannot be parsed as JSON document. | |The specified input cannot be parsed as JSON document. | ||
|- | |- | ||
− | |{{Code| | + | |{{Code|serialize}} |
|The specified node cannot be serialized as JSON document. | |The specified node cannot be serialized as JSON document. | ||
− | |||
− | |||
− | |||
|} | |} | ||
=Changelog= | =Changelog= | ||
+ | |||
+ | ;Version 9.4 | ||
+ | * Added: [[#json:doc|json:doc]] | ||
+ | |||
+ | ; Version 9.1 | ||
+ | * Updated: [[#json:parse|json:parse]] can be called with empty sequence. | ||
+ | |||
+ | ;Version 9.0 | ||
+ | * Updated: <code>map</code> format renamed to <code>xquery</code>. | ||
+ | * Updated: error codes updated; errors now use the module namespace | ||
+ | |||
+ | ;Version 8.4 | ||
+ | * Updated: <code>unescape</code> changed to <code>escape</code>. | ||
+ | |||
+ | ;Version 8.2 | ||
+ | * Added: Conversion format <code>[[#Basic|basic]]</code>. | ||
+ | |||
+ | ;Version 8.0 | ||
+ | * Updated: Serialization aligned with the {{Code|json}} output method of the official specification. | ||
+ | * Added: {{Code|liberal}} option. | ||
+ | * Removed: {{Code|spec}} option. | ||
+ | |||
+ | ;Version 7.8 | ||
+ | * Removed: {{Code|json:parse-ml}}, {{Code|json:serialize-ml}}. | ||
+ | * Updated: {{Code|json:parse}} now returns a document node instead of an element, or an XQuery map if {{Code|format}} is set to {{Code|.map}}. | ||
;Version 7.7.2 | ;Version 7.7.2 | ||
− | * Updated: {{Code|$options}} argument added to [[#json:parse|json:parse]] and [[#json:serialize|json:serialize]] | + | * Updated: {{Code|$options}} argument added to [[#json:parse|json:parse]] and [[#json:serialize|json:serialize]]. |
− | * Updated: [[#json:parse-ml|json:parse-ml]] and [[#json:serialize-ml|json:serialize-ml]] are now ''deprecated'' | + | * Updated: [[#json:parse-ml|json:parse-ml]] and [[#json:serialize-ml|json:serialize-ml]] are now ''deprecated''. |
The module was introduced with Version 7.0. | The module was introduced with Version 7.0. | ||
− | |||
− |
Revision as of 12:06, 2 July 2020
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. | 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
|
yes
|
serialize |
Functions
json:parse
Signatures | json:parse($string as xs:string?) as item()? json:parse($string as xs:string?, $options as map(*)?) as item()?
|
Summary | Converts the JSON $string to an XQuery value. If the input can be successfully parsed, it can be serialized back to the original JSON representation. The $options argument can be used to control the way the input is converted.
|
Errors | parse : the specified input cannot be parsed as JSON document.options : the specified options are conflicting.
|
json:doc
Signatures | json:doc($uri as xs:string) as item()? json:doc($uri as xs:string, $options as map(*)?) as item()? |
Summary | Fetches the JSON document referred to by the given $uri and converts it to an XQuery value. The $options argument can be used to control the way the input is converted.
|
Errors | parse : the specified input cannot be parsed as JSON document.options : the specified options are conflicting.
|
json:serialize
Signatures | json:serialize($input as item()?) as xs:string json:serialize($input as item()?, $options as 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 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 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.