Xpath与JsonPath符号对比@H_403_2@
JSONPath表达式
JSONPath表达式总是以与XPath相同的方式引用JSON结构@H_403_2@
表达式与XML文档结合使用。 由于JSON结构是@H_403_2@
通常是匿名的，并不一定有* root成员对象* JSONPath@H_403_2@
JSONPath表达式可以使用点符号:@H_403_2@
$.store.book[0].title
或方括号:@H_403_2@
$['store']['book'][0]['title']
为输入路径。内部或输出路径将始终转换为更一般的方括号。@H_403_2@
JSONPath允许成员名称和数组索引使用通配符*. 它从E4X和数组切片语法借用后代运算符..
来自ECMASCRIPT 4的提议[start:end:step].@H_403_2@
底层脚本语言(<expr>)的表达式可以用作一个
显式名称或索引的替代，如下所示：@H_403_2@
$.store.book[(@.length-1)].title
Filter expressions are supported via
the Syntax ?(<boolean expr>),as in:
使用符号@ 作为当前对象。过滤器表达式通过
语法?(<boolean expr>)，如下所示：@H_403_2@
$.store.book[?(@.price < 10)].title
以下是对JSONPath的完整概述和并排比较语法元素与XPath相对应：@H_403_2@
| XPath | JSONPath | Description |
|---|---|---|
/ |
$ |
The root object/element |
. |
@ |
The current object/element |
/ |
. or [] |
Child operator |
.. |
n/a | Parent operator |
// |
.. |
Recursive descent. JSONPath borrows this Syntax from E4X. |
* |
* |
Wildcard. All objects/elements regardless their names. |
@ |
n/a | Attribute access. JSON structures don’t have attributes. |
[] |
[] |
Subscript operator. XPath uses it to iterate over element collections and for predicates. In Javascript and JSON it is the native array operator. |
| ` | ` | [,] |
| n/a | [start:end:step] |
Array slice operator borrowed from ES4. |
[] |
?() |
Applies a filter (script) expression. |
| n/a | () |
Script expression,using the underlying script engine. |
() |
n/a | Grouping in XPath |
示例
让我们通过更多的例子来练习JSONPath表达式。 我们从一开始
在代表书店的XML示例之后构建的简单JSON结构：@H_403_2@
{ "store": { "book": [ { "category": "reference","author": "Nigel Rees","title": "Sayings of the Century","price": 8.95 },{ "category": "fiction","author": "Evelyn Waugh","title": "Sword of Honour","price": 12.99 },"author": "Herman Melville","title": "Moby Dick","isbn": "0-553-21311-3","price": 8.99 },"author": "J. R. R. Tolkien","title": "The Lord of the Rings","isbn": "0-395-19395-8","price": 22.99 } ],"bicycle": { "color": "red","price": 19.95 } } }
| XPath | JSONPath | Result | Notes |
|---|---|---|---|
/store/book/author |
$.store.book[*].author |
The authors of all books in the store | |
//author |
$..author |
All authors | |
/store/* |
$.store.* |
All things in store,which are some books and a red bicycle | |
/store//price |
$.store..price |
The price of everything in the store | |
//book[3] |
$..book[2] |
The third book | |
//book[last()] |
$..book[(@.length-1)]<br>$..book[-1:] |
The last book in order | |
//book[position()<3] |
$..book[0,1]$..book[:2] |
The first two books | |
| `//book/*[self::category | self::author]or//book/(category,author)` in XPath 2.0 |
$..book[category,author] |
The categories and authors of all books |
//book[isbn] |
$..book[?(@.isbn)] |
Filter all books with isbn number |
|
//book[price<10] |
$..book[?(@.price<10)] |
Filter all books cheapier than 10 | |
//*[price>19]/.. |
$..[?(@.price>19)] |
Categories with things more expensive than 19 | Parent (caret) not present in original spec |
//* |
$..* |
All elements in XML document; all members of JSON structure | |
/store/book/[position()!=1] |
$.store.book[?(@path !== "$[\'store\'][\'book\'][0]")] |
All books besides that at the path pointing to the first | @path not present in original spec |
JsonPath.cs
namespace JsonPath
{
#region Imports
using System;
using System.Collections;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
#endregion
public interface IJsonPathValueSystem
{
bool HasMember(object value,string member);
object GetMemberValue(object value,string member);
IEnumerable<string> GetMembers(object value);
bool IsObject(object value);
bool IsArray(object value);
bool IsPrimitive(object value);
}
public sealed class JsonPathContext
{
public static readonly JsonPathContext Default = new JsonPathContext();
public Func<string /* script */,object /* value */,string /* context */,object /* result */>
ScriptEvaluator { get; set; }
public IJsonPathValueSystem ValueSystem { get; set; }
public IEnumerable<object> Select(object obj,string expr)
{
return SelectNodes(obj,expr,(v,_) => v);
}
public IEnumerable<T> SelectNodes<T>(object obj,string expr,Func<object,string,T> resultor)
{
if (obj == null) throw new ArgumentNullException("obj");
if (resultor == null) throw new ArgumentNullException("resultor");
var i = new Interpreter(ValueSystem,ScriptEvaluator);
expr = Normalize(expr);
if (expr.Length >= 1 && expr[0] == '$') // ^\$:?
expr = expr.Substring(expr.Length >= 2 && expr[1] == ';' ? 2 : 1);
return i.Trace(expr,obj,"$",(value,path) => resultor(value,AsBracketNotation(path)));
}
static string Normalize(string expr)
{
var subx = new List<string>();
expr = RegExp.Replace(expr,@"[\['](\??\(.*?\))[\]']",m =>
{
subx.Add(m.Groups[1].Value);
return "[#" + subx.Count.ToString(CultureInfo.InvariantCulture) + "]";
});
expr = RegExp.Replace(expr,@"'?\.'?|\['?",";");
expr = RegExp.Replace(expr,@";;;|;;",";..;");
expr = RegExp.Replace(expr,@";$|'?\]|'$",string.Empty);
expr = RegExp.Replace(expr,@"#([0-9]+)",m =>
{
var index = int.Parse(m.Groups[1].Value,CultureInfo.InvariantCulture);
return subx[index];
});
return expr;
}
public static string AsBracketNotation(string[] indicies)
{
if (indicies == null)
throw new ArgumentNullException("indicies");
var sb = new StringBuilder();
foreach (var index in indicies)
{
if (sb.Length == 0)
{
sb.Append('$');
}
else
{
sb.Append('[');
if (RegExp.IsMatch(index,@"^[0-9*]+$"))
sb.Append(index);
else
sb.Append('\'').Append(index).Append('\'');
sb.Append(']');
}
}
return sb.ToString();
}
static int ParseInt(string str,int defaultValue = 0)
{
if (string.IsNullOrEmpty(str))
return defaultValue;
try
{
return int.Parse(str,NumberStyles.None,CultureInfo.InvariantCulture);
}
catch (FormatException)
{
return defaultValue;
}
}
sealed class Interpreter
{
readonly Func<string,object,object> _eval;
readonly IJsonPathValueSystem _system;
static readonly IJsonPathValueSystem DefaultValueSystem = new BasicValueSystem();
static readonly char[] Colon = { ':' };
static readonly char[] Semicolon = { ';' };
delegate void WalkCallback(object member,string loc,object value,string path);
public Interpreter(IJsonPathValueSystem valueSystem,Func<string,object> eval)
{
_eval = eval ?? delegate
{
// expr中的@符号必须专门解释才能解析为值。 在JavaScript中，实现将如下所示：
// return obj && value && eval(expr.replace(/@/g,"value"));
return null;
};
_system = valueSystem ?? DefaultValueSystem;
}
sealed class TraceArgs
{
public readonly string Expr;
public readonly object Value;
public readonly string Path;
public TraceArgs(string expr,string path)
{
Expr = expr;
Value = value;
Path = path;
}
}
public IEnumerable<T> Trace<T>(string expr,string path,string[],T> resultor)
{
return Trace(Args(expr,value,path),resultor);
}
static TraceArgs Args(string expr,string path)
{
return new TraceArgs(expr,path);
}
IEnumerable<T> Trace<T>(TraceArgs args,T> resultor)
{
var stack = new Stack<TraceArgs>();
stack.Push(args);
while (stack.Count > 0)
{
var popped = stack.Pop();
var expr = popped.Expr;
var value = popped.Value;
var path = popped.Path;
if (string.IsNullOrEmpty(expr))
{
if (path != null)
yield return resultor(value,path.Split(Semicolon));
continue;
}
var i = expr.IndexOf(';');
var atom = i >= 0 ? expr.Substring(0,i) : expr;
var tail = i >= 0 ? expr.Substring(i + 1) : string.Empty;
if (value != null && _system.HasMember(value,atom))
{
stack.Push(Args(tail,Index(value,atom),path + ";" + atom));
}
else if (atom == "*")
{
Walk(atom,tail,path,(m,l,x,v,p) => stack.Push(Args(m + ";" + x,p)));
}
else if (atom == "..")
{
Walk(atom,p) =>
{
var result = Index(v,m.ToString());
if (result != null && !_system.IsPrimitive(result))
stack.Push(Args("..;" + x,result,p + ";" + m));
});
stack.Push(Args(tail,path));
}
else if (atom.Length > 2 && atom[0] == '(' && atom[atom.Length - 1] == ')') // [(exp)]
{
stack.Push(Args(_eval(atom,path.Substring(path.LastIndexOf(';') + 1)) + ";" + tail,path));
}
else if (atom.Length > 3 && atom[0] == '?' && atom[1] == '(' && atom[atom.Length - 1] == ')') // [?(exp)]
{
Walk(atom,p) =>
{
var result = _eval(RegExp.Replace(l,@"^\?\((.*?)\)$","$1"),Index(v,m.ToString()),m.ToString());
if (Convert.ToBoolean(result,CultureInfo.InvariantCulture))
stack.Push(Args(m + ";" + x,p));
});
}
else if (RegExp.IsMatch(atom,@"^(-?[0-9]*):(-?[0-9]*):?([0-9]*)$")) // [start:end:step] Phyton slice Syntax
{
foreach (var a in Slice(atom,path).Reverse())
stack.Push(a);
}
else if (atom.IndexOf(',') >= 0) // [name1,name2,...]
{
foreach (var part in RegExp.Split(atom,@"'?,'?").Reverse())
stack.Push(Args(part + ";" + tail,path));
}
}
}
void Walk(string loc,WalkCallback callback)
{
if (_system.IsPrimitive(value))
return;
if (_system.IsArray(value))
{
var list = (IList) value;
for (var i = list.Count - 1; i >= 0; i--)
callback(i,loc,path);
}
else if (_system.IsObject(value))
{
foreach (var key in _system.GetMembers(value).Reverse())
callback(key,path);
}
}
static IEnumerable<TraceArgs> Slice(string loc,string path)
{
var list = value as IList;
if (list == null)
yield break;
var length = list.Count;
var parts = loc.Split(Colon);
var start = ParseInt(parts[0]);
var end = ParseInt(parts[1],list.Count);
var step = parts.Length > 2 ? ParseInt(parts[2],1) : 1;
start = (start < 0) ? Math.Max(0,start + length) : Math.Min(length,start);
end = (end < 0) ? Math.Max(0,end + length) : Math.Min(length,end);
for (var i = start; i < end; i += step)
yield return Args(i + ";" + expr,path);
}
object Index(object obj,string member)
{
return _system.GetMemberValue(obj,member);
}
}
static class RegExp
{
const RegexOptions Options = RegexOptions.ECMAScript;
public static bool IsMatch(string input,string pattern)
{
return Regex.IsMatch(input,pattern,Options);
}
public static string Replace(string input,string pattern,string replacement)
{
return Regex.Replace(input,replacement,MatchEvaluator evaluator)
{
return Regex.Replace(input,evaluator,Options);
}
public static IEnumerable<string> Split(string input,string pattern)
{
return Regex.Split(input,Options);
}
}
sealed class BasicValueSystem : IJsonPathValueSystem
{
public bool HasMember(object value,string member)
{
if (IsPrimitive(value))
return false;
var dict = value as IDictionary;
if (dict != null)
return dict.Contains(member);
var list = value as IList;
if (list != null)
{
var index = ParseInt(member,-1);
return index >= 0 && index < list.Count;
}
return false;
}
public object GetMemberValue(object value,string member)
{
if (IsPrimitive(value))
throw new ArgumentException("value");
var dict = value as IDictionary;
if (dict != null)
return dict[member];
var list = (IList) value;
var index = ParseInt(member,-1);
if (index >= 0 && index < list.Count)
return list[index];
return null;
}
public IEnumerable<string> GetMembers(object value)
{
return ((IDictionary) value).Keys.Cast<string>();
}
public bool IsObject(object value)
{
return value is IDictionary;
}
public bool IsArray(object value)
{
return value is IList;
}
public bool IsPrimitive(object value)
{
if (value == null)
throw new ArgumentNullException("value");
return Type.GetTypeCode(value.GetType()) != TypeCode.Object;
}
}
}
}
