System.JSON.TJSONPathParser
Delphi
TJSONPathParser = record
C++
struct DECLSPEC_DRECORD TJSONPathParser
{
public:
enum class DECLSPEC_DENUM TToken : unsigned char { Undefined, Name, ArrayIndex, Eof, Error };
private:
System::WideChar *FPathPtr;
System::WideChar *FPtr;
System::WideChar *FEndPtr;
int FTokenArrayIndex;
System::UnicodeString FTokenName;
TToken FToken;
bool __fastcall GetIsEof();
void __fastcall RaiseError(System::PResStringRec AMsg);
void __fastcall RaiseErrorFmt(System::PResStringRec AMsg, const System::TVarRec *AParams, const int AParams_High);
void __fastcall ParseName();
void __fastcall ParseQuotedName(System::WideChar AQuote);
void __fastcall ParseArrayIndex();
void __fastcall ParseIndexer();
bool __fastcall EnsureLength(int ALength);
void __fastcall FrontTrim(System::WideChar * &APtr);
void __fastcall BackTrim(System::WideChar * &APtr);
public:
__fastcall TJSONPathParser(const System::UnicodeString APath)/* overload */;
__fastcall TJSONPathParser(const System::WideChar * APathPtr, int ALen)/* overload */;
TToken __fastcall NextToken();
__property bool IsEof = {read=GetIsEof};
__property TToken Token = {read=FToken};
__property System::UnicodeString TokenName = {read=FTokenName};
__property int TokenArrayIndex = {read=FTokenArrayIndex};
TJSONPathParser() {}
};
Contents
Properties
Type | Visibility | Source | Unit | Parent |
---|---|---|---|---|
record struct |
public | System.JSON.pas System.JSON.hpp |
System.JSON | System.JSON |
Description
Parser of a JSON path.
A JSON path is a string that defines a path to a specific item within JSON data. A JSON path is to JSON what XPath is to XML.
Supported JSON Path Syntax
TJSONPathParser implements a subset of the JSON path specification defined by Stefan Göessner. Specifically, supported elements are:
- Child operators for objects:
- Use
.
to access object properties that do not contain a dot in their name. For example, useroot.child
to access thechild
property of theroot
object. - Use
[]
to access object properties that do contain a quoting character in their name. For example, useroot['child.name']
orroot["child.name"]
to access thechild.name
property of theroot
object.
- Use
- Subscript operator (
[]
) for arrays. For example, useroot[0]
to access the first item of theroot
array.
These operators do not support special expressions, they only support actual values (object properties or array indexes).
Using TJSONPathParser
When you create an instance of TJSONPathParser, you must pass the target JSON path to the constructor.
Once you have an instance of TJSONPathParser, call NextToken to iterate through the tokens of the specified JSON path until IsEof is True
or NextToken returns an Error token.
NextToken may return any of the following tokens:
Token | Description |
---|---|
|
The next token in the JSON path is the index of an item of a JSON array. TokenArrayIndex contains the target index. |
|
The next token in the JSON path is the key of a key-value pair of a JSON object. TokenName contains the target key. |
|
You have reached the end of the JSON path. You cannot continue iterating through the path, if you call NextToken again on this instance of TJSONPathParser an exception raises. |
|
There is an error in the specified JSON path. You cannot continue iterating through the path, if you call NextToken again on this instance of TJSONPathParser an exception raises. |
Token contains the token that the last call to NextToken returned.
For a code example that shows how to use TJSONPathParser, see the implementation of TJSONIterator.Find.