Newtonsoft.Json笔记 -JsonPath

参考：https://github.com/json-path/JsonPath

介绍

类似于XPath在xml文档中的定位，JsonPath表达式通常是用来路径检索或设置Json的。其表达式可以接受“dot–notation”和“bracket–notation”格式，例如$.store.book[0].title、$[‘store’][‘book’][0][‘title’]

操作符

符号	描述
$	查询的根节点对象，用于表示一个json数据，可以是数组或对象.
@	过滤器断言（filter predicate）处理的当前节点对象，类似于this.
*	通配符，可以表示一个名字或数字.
..	可以理解为递归搜索
.	表示一个子节点
['' (, '')]	表示一个或多个子节点
[ (, )]	表示一个或多个数组下标
[start:end]	数组片段，区间为[start,end),不包含end
[?()]	过滤器表达式，表达式结果必须是boolean.

过滤器操作符

过滤器是用于过滤数组的逻辑表达式，一个通常的表达式形如：[?(@.age > 18)]，可以通过逻辑表达式&&或||组合多个过滤器表达式，例如[?(@.price < 10 && @.category == ‘fiction’)]，字符串必须用单引号或双引号包围，例如[?(@.color == ‘blue’)] or [?(@.color == “blue”)]。

符号	描述
==	left is equal to right (note that 1 is not equal to '1')
!=	left is not equal to right
<	left is less than right
<=	left is less or equal to right
>	left is greater than right
>=	left is greater than or equal to right
=~	判断是否符合正则表达式，例如[?(@.name =~ /foo.*?/i)]
in	所属符号，例如[?(@.size in [‘S’, ‘M’])]
nin	排除符号
subsetof	left is a subset of right [?(@.sizes subsetof ['S', 'M', 'L'])]
anyof	left has an intersection with right [?(@.sizes anyof ['M', 'L'])]
noneof	left has no intersection with right [?(@.sizes noneof ['M', 'L'])]
size	size of left (array or string) should match right
empty	判空符号

JsonPath案例

json：

           string json = @"{
                            ""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
                                    },
                                    {
                                        ""category"": ""fiction"",
                                        ""author"": ""Herman Melville"",
                                        ""title"": ""Moby Dick"",
                                        ""isbn"": ""0-553-21311-3"",
                                        ""price"": 8.99
                                    },
                                    {
                                        ""category"": ""fiction"",
                                        ""author"": ""J. R. R. Tolkien"",
                                        ""title"": ""The Lord of the Rings"",
                                        ""isbn"": ""0-395-19395-8"",
                                        ""price"": 22.99
                                    }
                                ],
                                ""category"": ""store"",
                                ""bicycle"": {
                                    ""color"": ""red"",
                                    ""price"": 19.95
                                }
                            },
                            ""expensive"": 10
                        }
                         ";

代码：

            JObject jobj = JObject.Parse(json);
            //递归搜索，搜索所有category
            var tokens = jobj.SelectTokens("$..category");
            int tokenCount = tokens.Count();//5
            foreach (var token in tokens)
            {
               string value = token.ToString();
            }
            //reference、fiction、fiction、fiction、store

            //查询所有书的category
            tokens = jobj.SelectTokens("$.store.book[*].category");// or $.store..category
            tokenCount = tokens.Count();//4
            string tokenValue = tokens.ToList()[3].ToString();//fiction

            //查询所有书的category、price
            tokens = jobj.SelectTokens("$.store.book[*]['category','price']");// or $.store..category
            tokenCount = tokens.Count();//8
            tokenValue = tokens.ToList()[1].ToString();//8.95

            //查询数组指定下标的节点
            tokens = jobj.SelectTokens("$..book[0,1]").ToList();//前两个
            tokens = jobj.SelectTokens("$..book[:2]").ToList();//前两个
            tokens = jobj.SelectTokens("$..book[-2:]").ToList();//最后两个
            tokens = jobj.SelectTokens("$..book[2:]").ToList();//第三个及之后的


            //查询第一本书的所有叶子节点
            tokens = jobj.SelectTokens("$.store.book[0].*");
            tokenCount = tokens.Count();
            string price = tokens.ToList()[3].ToString();//8.95

            //查询第一本书的第一个叶子节点
            //tokens = jobj.SelectTokens("$.store.book[0][0]");
            //string category = tokens.First().ToString();//reference

            //查询所有节点
            tokens = jobj.SelectTokens("$..*");
            tokenCount = tokens.Count();//30

            //查询所有带isbn的书
            tokens = jobj.SelectTokens("$..book[?(@.isbn)]").ToList();
            tokenCount= tokens.Count();//2

            //查询价格小于20的书
            tokens = jobj.SelectTokens("$..book[?(@.price<20)]").ToList();
            tokenCount = tokens.Count();//3

            //查询价格小于expensive字段的书
            tokens = jobj.SelectTokens("$..book[?(@.price<$.expensive)]").ToList();
            tokenCount = tokens.Count();//2

            //查询符合正则表达式的书
            tokens = jobj.SelectTokens("$..book[?(@.author=~/^EVE/i)]").ToList();
            tokenCount = tokens.Count();//1

以下案例与JsonPath无关

JSON:

var json = @"{
   'course_editions': {
      '2014/SL': [
         {
            'grades': {
               'course_units_grades': {
                  '159715': {
                     '1': {
                        'value_symbol': '4','exam_session_number': 1,'exam_id': 198172,'value_description': {
                           'en': 'good'
                        }
                     }
                  }
               },'course_grades': {}
            }
         },{
            'grades': {
               'course_units_grades': {
                  '159796': {
                     '2': {
                        'value_symbol': '5','exam_id': 198259,'value_description': {
                           'en': 'very good'
                        }
                     }
                  }
               },'course_grades': {}
            }
         }
      ]
   }
}";

案例1

获取所有course_units_grades节点下的第一个属性的名称

var jobj = JObject.Parse(json);
var coursesTokens = jobj.SelectTokens("course_editions.2014/SL[*].grades.course_units_grades")
                        .Select(o => o.First) //get the first child of `course_units_grades`
                        .Cast<JProperty>() //cast to JProperty
                        .Select(o => o.Name); //get the name of the property
foreach (string coursesToken in coursesTokens)
{
    Console.WriteLine(coursesToken);
}

输出结果：

159715
159796

案例2

获取所有course_units_grades节点下的第一个属性值的第一个属性的名称

            var jobj = JObject.Parse(json);
            var coursesTokens = jobj.SelectTokens("course_editions.2014/SL[*].grades.course_units_grades")
                                    .Select(o => o.First) //get the first child of `course_units_grades`
                                    .Cast<JProperty>() //cast to JProperty
                                    .Select(o => o.Value) //get the name of the property
                                    .Select(o => o.First)
                                    .Cast<JProperty>() //cast to JProperty
                                    .Select(o => o.Name);
            foreach (string coursesToken in coursesTokens)
            {
                Console.WriteLine(coursesToken);
            }

输出结果：

1
2