We receive JSON data from Facebook Real Time subscription. The JSON itself contains property like "object":"page" and we need to access this property.
{
"entry":[
{
"changes":[ ],
"id":"1037501376337008",
"time":1465883784
}
],"object":"page"
}
We use dynamic object to parse the JSON but when we try to access the result.object, it is not allowed as object is the keyword in C#.
dynamic result = JsonConvert.DeserializeObject<dynamic>(jsonRealTimeNotification);
string objectType = result.object.ToString(); // This line does not build
We can replace the "object" by some text in the original JSON string and then parse but we are looking if there is a standard way to handle this
Use #object:
dynamic result = JsonConvert.DeserializeObject<dynamic>(jsonRealTimeNotification);
string objectType = result.#object.ToString();
This is the same syntax as is used when specifying a regular verbatim identifier. From the C# Language Specification, ยง 2.4.2 Identifiers (C#):
The prefix "#" enables the use of keywords as identifiers, which is useful when interfacing with other programming languages. The character # is not actually part of the identifier, so the identifier might be seen in other languages as a normal identifier, without the prefix. An identifier with an # prefix is called a verbatim identifier.
Sample fiddle.
Related
In my JSON file, one of the fields has to carry the content of another file (a string).
The string has CRLFs, single/double quotes, tabs.
Is there a way to consider my whole string as a raw string so I don't have to escape special characters?
Is there an equivalent in JSON to the string raw delimiter in C++?
In C++, I would just put the whole file content inside : R"( ... )"
Put simply, no there isn't. Depending on what parser you use, it may have a feature that allows this and/or there may be a variant of JSON that allows this (examples of variants include JSONP and JSON-C, though I'm not aware of one specifically that allows for the features you are looking for), but the JSON standard ubiquitous on the web does not support multiline strings or unescaped special characters.
A workaround for the lack of raw string support in JSON is to Base64 encode your string before adding it to your JSON.
I've carefully read the JSON description http://json.org/ but I'm not sure I know the answer to the simple question. What strings are the minimum possible valid JSON?
"string" is the string valid JSON?
42 is the simple number valid JSON?
true is the boolean value a valid JSON?
{} is the empty object a valid JSON?
[] is the empty array a valid JSON?
At the time of writing, JSON was solely described in RFC4627. It describes (at the start of "2") a JSON text as being a serialized object or array.
This means that only {} and [] are valid, complete JSON strings in parsers and stringifiers which adhere to that standard.
However, the introduction of ECMA-404 changes that, and the updated advice can be read here. I've also written a blog post on the issue.
To confuse the matter further however, the JSON object (e.g. JSON.parse() and JSON.stringify()) available in web browsers is standardised in ES5, and that clearly defines the acceptable JSON texts like so:
The JSON interchange format used in this specification is exactly that described by RFC 4627 with two exceptions:
The top level JSONText production of the ECMAScript JSON grammar may consist of any JSONValue rather than being restricted to being a JSONObject or a JSONArray as specified by RFC 4627.
snipped
This would mean that all JSON values (including strings, nulls and numbers) are accepted by the JSON object, even though the JSON object technically adheres to RFC 4627.
Note that you could therefore stringify a number in a conformant browser via JSON.stringify(5), which would be rejected by another parser that adheres to RFC4627, but which doesn't have the specific exception listed above. Ruby, for example, would seem to be one such example which only accepts objects and arrays as the root. PHP, on the other hand, specifically adds the exception that "it will also encode and decode scalar types and NULL".
There are at least four documents which can be considered JSON standards on the Internet. The RFCs referenced all describe the mime type application/json. Here is what each has to say about the top-level values, and whether anything other than an object or array is allowed at the top:
RFC-4627: No.
A JSON text is a sequence of tokens. The set of tokens includes six
structural characters, strings, numbers, and three literal names.
A JSON text is a serialized object or array.
JSON-text = object / array
Note that RFC-4627 was marked "informational" as opposed to "proposed standard", and that it is obsoleted by RFC-7159, which in turn is obsoleted by RFC-8259.
RFC-8259: Yes.
A JSON text is a sequence of tokens. The set of tokens includes six
structural characters, strings, numbers, and three literal names.
A JSON text is a serialized value. Note that certain previous
specifications of JSON constrained a JSON text to be an object or an
array. Implementations that generate only objects or arrays where a
JSON text is called for will be interoperable in the sense that all
implementations will accept these as conforming JSON texts.
JSON-text = ws value ws
RFC-8259 is dated December 2017 and is marked "INTERNET STANDARD".
ECMA-262: Yes.
The JSON Syntactic Grammar defines a valid JSON text in terms of tokens defined by the JSON lexical
grammar. The goal symbol of the grammar is JSONText.
Syntax
JSONText :
JSONValue
JSONValue :
JSONNullLiteral
JSONBooleanLiteral
JSONObject
JSONArray
JSONString
JSONNumber
ECMA-404: Yes.
A JSON text is a sequence of tokens formed from Unicode code points that conforms to the JSON value
grammar. The set of tokens includes six structural tokens, strings, numbers, and three literal name tokens.
According to the old definition in RFC 4627 (which was obsoleted in March 2014 by RFC 7159), those were all valid "JSON values", but only the last two would constitute a complete "JSON text":
A JSON text is a serialized object or array.
Depending on the parser used, the lone "JSON values" might be accepted anyway. For example (sticking to the "JSON value" vs "JSON text" terminology):
the JSON.parse() function now standardised in modern browsers accepts any "JSON value"
the PHP function json_decode was introduced in version 5.2.0 only accepting a whole "JSON text", but was amended to accept any "JSON value" in version 5.2.1
Python's json.loads accepts any "JSON value" according to examples on this manual page
the validator at http://jsonlint.com expects a full "JSON text"
the Ruby JSON module will only accept a full "JSON text" (at least according to the comments on this manual page)
The distinction is a bit like the distinction between an "XML document" and an "XML fragment", although technically <foo /> is a well-formed XML document (it would be better written as <?xml version="1.0" ?><foo />, but as pointed out in comments, the <?xml declaration is technically optional).
JSON stands for JavaScript Object Notation. Only {} and [] define a Javascript object. The other examples are value literals. There are object types in Javascript for working with those values, but the expression "string" is a source code representation of a literal value and not an object.
Keep in mind that JSON is not Javascript. It is a notation that represents data. It has a very simple and limited structure. JSON data is structured using {},:[] characters. You can only use literal values inside that structure.
It is perfectly valid for a server to respond with either an object description or a literal value. All JSON parsers should be handle to handle just a literal value, but only one value. JSON can only represent a single object at a time. So for a server to return more than one value it would have to structure it as an object or an array.
The ecma specification might be useful for reference:
http://www.ecma-international.org/ecma-262/5.1/
The parse function parses a JSON text (a JSON-formatted String) and produces an ECMAScript value. The
JSON format is a restricted form of ECMAScript literal. JSON objects are realized as ECMAScript objects.
JSON arrays are realized as ECMAScript arrays. JSON strings, numbers, booleans, and null are realized as
ECMAScript Strings, Numbers, Booleans, and null. JSON uses a more limited set of white space characters
than WhiteSpace and allows Unicode code points U+2028 and U+2029 to directly appear in JSONString literals
without using an escape sequence. The process of parsing is similar to 11.1.4 and 11.1.5 as constrained by
the JSON grammar.
JSON.parse("string"); // SyntaxError: Unexpected token s
JSON.parse(43); // 43
JSON.parse("43"); // 43
JSON.parse(true); // true
JSON.parse("true"); // true
JSON.parse(false);
JSON.parse("false");
JSON.parse("trueee"); // SyntaxError: Unexpected token e
JSON.parse("{}"); // {}
JSON.parse("[]"); // []
Yes, yes, yes, yes, and yes. All of them are valid JSON value literals.
However, the official RFC 4627 states:
A JSON text is a serialized object or array.
So a whole "file" should consist of an object or array as the outermost structure, which of course can be empty. Yet, many JSON parsers accept primitive values as well for input.
Just follow the railroad diagrams given on the json.org page. [] and {} are the minimum possible valid JSON objects. So the answer is [] and {}.
var x;
console.log(JSON.stringify(x)); // will output "{}"
So your answer is "{}" which denotes an empty object.
I'm using webwrite to post to an api. One of the field names in the json object I'm trying to setup for posting is odata.metadata. I'm making a struct that looks like this for the json object:
json = struct('odata.metadata', metadata, 'odata.type', type, 'Name', name,);
But I get an error
Error using struct
Invalid field name "odata.metadata"
Here's the json object I'm trying to use in Matlab. All strings for simplicity:
{
"odata.metadata": "https://website.com#Element",
"odata.type": "Blah.Blah.This.That",
"Name": "My Object"
}
Is there a way to submit this json object or is it a lost cause?
Field names are not allowed to have dots in them. The reason why is because this will be confused with accessing another nested structure within the structure itself.
For example, doing json.odata.metadata would be interpreted as json being a struct with a member whose field name is odata where odata has another member whose field name is metadata. This would not be interpreted as a member with the combined field name as odata.metadata. You're going to have to rename the field to something else or change the convention of your field name slightly.
Usually, the convention is to replace dots with underscores. An automated way to take care of this if you're not willing to manually rename the field names yourself is to use a function called matlab.lang.makeValidName that takes in a string and converts it into a valid field name. This function was introduced in R2014a. For older versions, it's called genvarname.
For example:
>> matlab.lang.makeValidName('odata.metadata')
ans =
odata_metadata
As such, either replace all dots with _ to ensure no ambiguities or use matlab.lang.makeValidName or genvarname to take care of this for you.
I would suggest using a a containers.Map instead of a struct to store your data, and then creating your JSON string by iterating over the Map filednames and appending them along with the data to your JSON.
Here's a quick demonstration of what I mean:
%// Prepare the Map and the Data:
metadata = 'https://website.com#Element';
type = 'Blah.Blah.This.That';
name = 'My Object';
example_map = containers.Map({'odata.metadata','odata.type','Name'},...
{metadata,type,name});
%// Convert to JSON:
JSONstr = '{'; %// Initialization
map_keys = keys(example_map);
map_vals = values(example_map);
for ind1 = 1:example_map.Count
JSONstr = [JSONstr '"' map_keys{ind1} '":"' map_vals{ind1} '",'];
end
JSONstr =[JSONstr(1:end-1) '}']; %// Finalization (get rid of the last ',' and close)
Which results in a valid JSON string.
Obviously if your values aren't strings you'll need to convert them using num2str etc.
Another alternative you might want to consider is the JSONlab FEX submission. I saw that its savejson.m is able to accept cell arrays - which can hold any string you like.
Other alternatives may include any of the numerous Java or python JSON libraries which you can call from MATLAB.
I probably shouldn't add this as an answer - but you can have '.' in a struct fieldname...
Before I go further - I do not advocate this and it will almost certainly cause bugs and a lot of trouble down the road... #rayryeng method is a better approach
If your struct is created by a mex function which creates a field that contains a "." -> then you will get what your after.
To create your own test see the Mathworks example and modify accordingly.
(I wont put the full code here to discourage the practice).
If you update the char example and compile to test_mex you get:
>> obj = test_mex
obj =
Doublestuff: [1x100 double]
odata.metadata: 'This is my char'
Note: You can only access your custom field in Matlab using dynamic fieldnames:
obj.('odata.metadata')
You need to use a mex capability to update it...
Similar to toString is there a way we can convert a string to BSON object? I need to remove a document using C++ driver the the remove function expects the query to have BSON object.
Use the fromjson method found here:
http://api.mongodb.org/cplusplus/1.5.4/namespacemongo.html#a4f542be0d0f9bad2d8cb32c3436026c2
BSONObj mongo::fromjson ( const string & str )
Create a BSONObj from a JSON <http://www.json.org> string.
In addition to the JSON extensions extensions described here
http://mongodb.onconfluence.com/display/DOCS/Mongo+Extended+JSON, this function accepts
certain unquoted field names and allows single quotes to optionally be used when
specifying field names and string values instead of double quotes. JSON unicode escape
sequences (of the form ) are converted to utf8.
Exceptions:
MsgAssertionException if parsing fails. The message included with this assertion includes
a rough indication of where parsing failed.
Part of a website's JSON response had this (... added for context):
{..., now:function(){return(new Date).getTime()}, ...}
Is adding anonymous functions to JSON valid? I would expect each time you access 'time' to return a different value.
No.
JSON is purely meant to be a data description language. As noted on http://www.json.org, it is a "lightweight data-interchange format." - not a programming language.
Per http://en.wikipedia.org/wiki/JSON, the "basic types" supported are:
Number (integer, real, or floating
point)
String (double-quoted Unicode
with backslash escaping)
Boolean
(true and false)
Array (an ordered
sequence of values, comma-separated
and enclosed in square brackets)
Object (collection of key:value
pairs, comma-separated and enclosed
in curly braces)
null
The problem is that JSON as a data definition language evolved out of JSON as a JavaScript Object Notation. Since Javascript supports eval on JSON, it is legitimate to put JSON code inside JSON (in that use-case). If you're using JSON to pass data remotely, then I would say it is bad practice to put methods in the JSON because you may not have modeled your client-server interaction well. And, further, when wishing to use JSON as a data description language I would say you could get yourself into trouble by embedding methods because some JSON parsers were written with only data description in mind and may not support method definitions in the structure.
Wikipedia JSON entry makes a good case for not including methods in JSON, citing security concerns:
Unless you absolutely trust the source of the text, and you have a need to parse and accept text that is not strictly JSON compliant, you should avoid eval() and use JSON.parse() or another JSON specific parser instead. A JSON parser will recognize only JSON text and will reject other text, which could contain malevolent JavaScript. In browsers that provide native JSON support, JSON parsers are also much faster than eval. It is expected that native JSON support will be included in the next ECMAScript standard.
Let's quote one of the spec's - https://www.rfc-editor.org/rfc/rfc7159#section-12
The The JavaScript Object Notation (JSON) Data Interchange Format Specification states:
JSON is a subset of JavaScript but excludes assignment and invocation.
Since JSON's syntax is borrowed from JavaScript, it is possible to
use that language's "eval()" function to parse JSON texts. This
generally constitutes an unacceptable security risk, since the text
could contain executable code along with data declarations. The same
consideration applies to the use of eval()-like functions in any
other programming language in which JSON texts conform to that
language's syntax.
So all answers which state, that functions are not part of the JSON standard are correct.
The official answer is: No, it is not valid to define functions in JSON results!
The answer could be yes, because "code is data" and "data is code".
Even if JSON is used as a language independent data serialization format, a tunneling of "code" through other types will work.
A JSON string might be used to pass a JS function to the client-side browser for execution.
[{"data":[["1","2"],["3","4"]],"aFunction":"function(){return \"foo bar\";}"}]
This leads to question's like: How to "https://stackoverflow.com/questions/939326/execute-javascript-code-stored-as-a-string".
Be prepared, to raise your "eval() is evil" flag and stick your "do not tunnel functions through JSON" flag next to it.
It is not standard as far as I know. A quick look at http://json.org/ confirms this.
Nope, definitely not.
If you use a decent JSON serializer, it won't let you serialize a function like that. It's a valid OBJECT, but not valid JSON. Whatever that website's intent, it's not sending valid JSON.
JSON explicitly excludes functions because it isn't meant to be a JavaScript-only data
structure (despite the JS in the name).
A short answer is NO...
JSON is a text format that is completely language independent but uses
conventions that are familiar to programmers of the C-family of
languages, including C, C++, C#, Java, JavaScript, Perl, Python, and
many others. These properties make JSON an ideal data-interchange
language.
Look at the reason why:
When exchanging data between a browser and a server, the data can only
be text.
JSON is text, and we can convert any JavaScript object into JSON, and
send JSON to the server.
We can also convert any JSON received from the server into JavaScript
objects.
This way we can work with the data as JavaScript objects, with no
complicated parsing and translations.
But wait...
There is still ways to store your function, it's widely not recommended to that, but still possible:
We said, you can save a string... how about converting your function to a string then?
const data = {func: '()=>"a FUNC"'};
Then you can stringify data using JSON.stringify(data) and then using JSON.parse to parse it (if this step needed)...
And eval to execute a string function (before doing that, just let you know using eval widely not recommended):
eval(data.func)(); //return "a FUNC"
Via using NodeJS (commonJS syntax) I was able to get this type of functionality working, I originally had just a JSON structure inside some external JS file, but I wanted that structure to be more of a Class, with methods that could be decided at run time.
The declaration of 'Executor' in myJSON is not required.
var myJSON = {
"Hello": "World",
"Executor": ""
}
module.exports = {
init: () => { return { ...myJSON, "Executor": (first, last) => { return first + last } } }
}
Function expressions in the JSON are completely possible, just do not forget to wrap it in double quotes. Here is an example taken from noSQL database design:
{
"_id": "_design/testdb",
"views": {
"byName": {
"map": "function(doc){if(doc.name){emit(doc.name,doc.code)}}"
}
}
}
although eval is not recommended, this works:
<!DOCTYPE html>
<html>
<body>
<h2>Convert a string written in JSON format, into a JavaScript function.</h2>
<p id="demo"></p>
<script>
function test(val){return val + " it's OK;}
var someVar = "yup";
var myObj = { "func": "test(someVar);" };
document.getElementById("demo").innerHTML = eval(myObj.func);
</script>
</body>
</html>
Leave the quotes off...
var a = {"b":function(){alert('hello world');} };
a.b();