JSON Concepts: Difference between revisions
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=External= | |||
* https://www.ietf.org/rfc/rfc4627.txt | |||
=Internal= | =Internal= | ||
* [[JSON#Subjects|JSON]] | * [[JSON#Subjects|JSON]] | ||
=Top-Level Element= | =JSON Document= | ||
The terms JSON document and JSON structure are used interchangeably. A JSON document consists in [[#Element|elements]] arranged in hierarchical structure, starting from the document root, or the [[#Top-Level_Element|top-level element]]. Each element is uniquely identified by a [[#Path|path]], starting from root. | |||
==Element== | |||
===Top-Level Element=== | |||
The top level element has always one of the [[#Data_Types|JSON data types]]. However, according to RFC4627, it seems that the a valid top level element can only be an [[#Object|Object]] <code>{...}</code> or an [[#Array|Array]] <code>[...]</code>, and noting else, so a string would not be a valid RFC4627 JSON content. | |||
If it's a [[#Booleans|boolean]], [[#Numbers|number]] or [[#Strings|string]], the entire content consists of that sole element. For a complex, recursive content, the top element is either an [[#Objects|Object]], so it starts with "{" or an [[#Arrays|Array]], so it starts with "[". | |||
==Path== | |||
Each [[#Element|element]] of a JSON document is uniquely identified by a [[#Path|path]], starting from root. [[JSONPath#JSONPath_Expression|JSONPath expressions]] can be used to specify paths, or filters that select paths. | |||
=Data Types= | =Data Types= | ||
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</pre> | </pre> | ||
and they ''must'' be quoted. Always use double quotes ("), never use single quotes ('). Single quotes are only accepted if the parser was configured so, which is not the default. | and they '''must''' be quoted. This constraint helps with semantics: if we see a number in a JSON context, we know it's a number, unless is quoted, in which case we know it's a string. | ||
Always use double quotes ("), never use single quotes ('). Single quotes are only accepted if the parser was configured so, which is not the default. See "[[#Single_Quotes_vs._Double_Quotes|Single Quotes vs. Double Quotes]]" below. | |||
==Numbers== | ==Numbers== | ||
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and they are not quoted. | and they are not quoted. | ||
==Objects== | ==<span id='Object'></span>Objects== | ||
Objects are enclosed in curly brackets "{}" and contain [[#Field|fields]]. | Objects are enclosed in curly brackets "{}" and contain [[#Field|fields]]. | ||
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</pre> | </pre> | ||
==Fields== | ===<span id='Field'><span>Fields=== | ||
A ''field'' is a key-value pair, where the key, or the ''field name'', is always a [[#Strings|string]]. | A ''field'' is a key-value pair, where the key, or the ''field name'', is always a [[#Strings|string]]. | ||
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} | } | ||
</pre> | </pre> | ||
=Single Quotes vs. Double Quotes= | =Single Quotes vs. Double Quotes= | ||
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=JSON Schema= | =JSON Schema= | ||
JSON Schema | {{Internal|JSON Schema|JSON Schema}} | ||
} | |||
=Collection+JSON= | =Collection+JSON= | ||
Collection+JSON is a JSON-based read/write hypermedia-type designed to support management and querying of simple collections. More details http://amundsen.com/media-types/collection/. | Collection+JSON is a JSON-based read/write hypermedia-type designed to support management and querying of simple collections. More details http://amundsen.com/media-types/collection/. | ||
=Conversion between YAML and JSON= | |||
{{Internal|Conversion between YAML and JSON|Conversion between YAML and JSON}} | |||
Latest revision as of 00:24, 16 March 2021
External
Internal
JSON Document
The terms JSON document and JSON structure are used interchangeably. A JSON document consists in elements arranged in hierarchical structure, starting from the document root, or the top-level element. Each element is uniquely identified by a path, starting from root.
Element
Top-Level Element
The top level element has always one of the JSON data types. However, according to RFC4627, it seems that the a valid top level element can only be an Object {...} or an Array [...], and noting else, so a string would not be a valid RFC4627 JSON content.
If it's a boolean, number or string, the entire content consists of that sole element. For a complex, recursive content, the top element is either an Object, so it starts with "{" or an Array, so it starts with "[".
Path
Each element of a JSON document is uniquely identified by a path, starting from root. JSONPath expressions can be used to specify paths, or filters that select paths.
Data Types
JSON data types are: null, Booleans, Strings, Numbers, Objects (which can be thought of as Maps) and Arrays.
null
null is represented as a lowercase literal:
null
Booleans
Booleans are represented as lowercase literals:
true false
and they are not quoted.
Strings
Strings are represented as:
"this is a string"
and they must be quoted. This constraint helps with semantics: if we see a number in a JSON context, we know it's a number, unless is quoted, in which case we know it's a string.
Always use double quotes ("), never use single quotes ('). Single quotes are only accepted if the parser was configured so, which is not the default. See "Single Quotes vs. Double Quotes" below.
Numbers
Numbers are represented as:
10
and they are not quoted.
Objects
Objects are enclosed in curly brackets "{}" and contain fields.
The field name and the value are separated by colon (":"). The pairs are delimited by commas (",").
The field name is always a string, so it must be quoted.
{
"id" : 42,
"name" : "John Doe",
"married" : true
"kids" : [ "Alice", "Bob" ]
}
Fields
A field is a key-value pair, where the key, or the field name, is always a string.
The JSON RFC refers to the key as "names". Jackson refers to them as "field names".
The field name, is separated by the value by a semicolon (:). The value can have any of the JSON data types.
Fields can only exist inside of a JSON Object.
Arrays
Array elements are enclosed in brackets "[", and they are separated by commas:
[ "one element", "another element" ]
Comments
JSON does not support comments: https://plus.google.com/+DouglasCrockfordEsq/posts/RK8qyGVaGSr
A comment can be simulated as follows:
{
"comment":"this is a comment",
...
}
Single Quotes vs. Double Quotes
Never use single quotes ('), always use double quotes ("). Single quotes are only accepted if the parser was configured so, which is not the default.
JSON Schema
Collection+JSON
Collection+JSON is a JSON-based read/write hypermedia-type designed to support management and querying of simple collections. More details http://amundsen.com/media-types/collection/.