How to filter a JSON by a string value contained in an array inside JSON using JSONPath

Question

I am listing down my sample JSON below, I want to write a JSONPath that selects element when subjects has (or contains) "Maths".

NOTE: I am using Goessner's JSONPath using Newtonsoft library (C#)**

{
   "class":{
      "type":"group",
      "identifier":"MyFavClass",
      "subs":[
         {
            "type":"individual",
            "identifier":"Rambo"
         },
         {
            "type":"individual",
            "identifier":"Rancho"
         },
         {
            "type":"biggroup",
            "identifier":"village",
            "subjects":[
               "Maths",
               "English"
            ]
         },
         {
            "type":"biggroup",
            "identifier":"newvillage",
            "subjects":[
               "Maths"
            ]
         }
      ]
   }
}

Answer 1

Assuming you are using Json.NET's SelectTokens() method for your JSONPath queries, you may find all math subjects using the following query:

var value = "Maths";

var subjects = root.SelectTokens($"class.subs[*].subjects[?(@ == '{value}')]");

Of course this will just return a sequence of JValue tokens with value "Maths" . If you want the class.subs[*] objects whose subjects[*] arrays contains "Maths" , you may do:

var subs = root.SelectTokens($"class.subs[?(@.subjects[?(@ == '{value}')])]");

Notes:

• [?(...)] applies a filter expression ... to an array.

• In a filter expression, array contents that are primitive values may be matched using the @ symbol for the current object.

• Json.NET's implementation of JSONPath supports nested queries inside array filter expressions. Thus [?(@.subjects[?(@ == '{value}')])] matches array items that have an item in their "subjects" array that matches the value parameter.

• Note that search values that contain a single quote character ' must be escaped as shown in Querying JSON with JSON Path and escaped properties . Thus if the string to be matched was Math's you would need to escape it like so:

   var value = "Math's".Replace("'", "\\\'");

Demo fiddle here .