Expressions in JSONPath
 
Usage of Expressions in JsonPath is a very good feature to have concise and complex JsonPaths. Expressions in JsonPath are basically code snippets that evaluate to the Boolean value. Based  on the outcome only the nodes which meet the criteria are selected. Let  us see more about it, but before that make sure you have gone through  following tutorials on basics of Json and JsonPath

Json
Jsonpath

In this tutorial, we will use a sample Json which has a few items in the Array. Please copy the below Json in our JsonPath Evaluator
{
  "books": [
    {
      "isbn": "9781593275846",
      "title": "Eloquent JavaScript, Second Edition",
      "subtitle": "A Modern Introduction to Programming",
      "author": "Marijn Haverbeke",
      "published": "2014-12-14T00:00:00.000Z",
      "publisher": "No Starch Press",
      "pages": 472,
      "description": "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
      "website": "https://eloquentjavascript.net/"
    },
    {
      "isbn": "9781449331818",
      "title": "Learning JavaScript Design Patterns",
      "subtitle": "A JavaScript and jQuery Developer's Guide",
      "author": "Addy Osmani",
      "published": "2012-07-01T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 254,
      "description": "With Learning JavaScript Design Patterns, you'll learn how to write beautiful, structured, and maintainable JavaScript by applying classical and modern design patterns to the language. If you want to keep your code efficient, more manageable, and up-to-date with the latest best practices, this book is for you.",
      "website": "https://www.addyosmani.com/resources/essentialjsdesignpatterns/book/"
    },
    {
      "isbn": "9781449365035",
      "title": "Speaking JavaScript",
      "subtitle": "An In-Depth Guide for Programmers",
      "author": "Axel Rauschmayer",
      "published": "2014-02-01T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 460,
      "description": "Like it or not, JavaScript is everywhere these days-from browser to server to mobile-and now you, too, need to learn the language or dive deeper than you have. This concise book guides you into and through JavaScript, written by a veteran programmer who once found himself in the same position.",
      "website": "https://speakingjs.com/"
    },
    {
      "isbn": "9781491950296",
      "title": "Programming JavaScript Applications",
      "subtitle": "Robust Web Architecture with Node, HTML5, and Modern JS Libraries",
      "author": "Eric Elliott",
      "published": "2014-07-01T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 254,
      "description": "Take advantage of JavaScript's power to build robust web-scale or enterprise applications that are easy to extend and maintain. By applying the design patterns outlined in this practical book, experienced JavaScript developers will learn how to write flexible and resilient code that's easier-yes, easier-to work with as your code base grows.",
      "website": "https://chimera.labs.oreilly.com/books/1234000000262/index.html"
    },
    {
      "isbn": "9781593277574",
      "title": "Understanding ECMAScript 6",
      "subtitle": "The Definitive Guide for JavaScript Developers",
      "author": "Nicholas C. Zakas",
      "published": "2016-09-03T00:00:00.000Z",
      "publisher": "No Starch Press",
      "pages": 352,
      "description": "ECMAScript 6 represents the biggest update to the core of JavaScript in the history of the language. In Understanding ECMAScript 6, expert developer Nicholas C. Zakas provides a complete guide to the object types, syntax, and other exciting changes that ECMAScript 6 brings to JavaScript.",
      "website": "https://leanpub.com/understandinges6/read"
    },
    {
      "isbn": "9781491904244",
      "title": "You Don't Know JS",
      "subtitle": "ES6 & Beyond",
      "author": "Kyle Simpson",
      "published": "2015-12-27T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 278,
      "description": "No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the 'You Don’t Know JS' series, this compact guide focuses on new features available in ECMAScript 6 (ES6), the latest version of the standard upon which JavaScript is built.",
      "website": "https://github.com/getify/You-Dont-Know-JS/tree/master/es6%20&%20beyond"
    },
    {
      "isbn": "9781449325862",
      "title": "Git Pocket Guide",
      "subtitle": "A Working Introduction",
      "author": "Richard E. Silverman",
      "published": "2013-08-02T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 234,
      "description": "This pocket guide is the perfect on-the-job companion to Git, the distributed version control system. It provides a compact, readable introduction to Git for new users, as well as a reference to common commands and procedures for those of you with Git experience.",
      "website": "https://chimera.labs.oreilly.com/books/1230000000561/index.html"
    },
    {
      "isbn": "9781449337711",
      "title": "Designing Evolvable Web APIs with ASP.NET",
      "subtitle": "Harnessing the Power of the Web",
      "author": "Glenn Block, et al.",
      "published": "2014-04-07T00:00:00.000Z",
      "publisher": "O'Reilly Media",
      "pages": 538,
      "description": "Design and build Web APIs for a broad range of clients—including browsers and mobile devices—that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft’s ASP.NET Web API framework. In the process, you’ll learn how design and implement a real-world Web API.",
      "website": "https://chimera.labs.oreilly.com/books/1234000001708/index.html"
    }
  ]
}

Expressions in JsonPath
Expressions in JsonPath are one of the most powerful features of JsonPath. Note that expressions are also available in Xpath and CSS Selectors.  Expressions help you create a condition that is evaluated to true or  false. There are two important symbols that you have to understand  before you can create Expressions in JsonPath.

? : Question mark, marks the beginning of an expression. Syntax used [? (Expression)]
@ : At symbol, signifies the current node being processed. Syntax used $.books[?(@.price > 100)]

Let us now take a simple task from the Json above.

Find out all the books which have the pages greater than 460

To create a JsonPath which can get us all the books which have pages  greater than 460, we have to break the problem into two parts

Create a JsonPath to retrieve all books
Append an expression to filter all the books which have pages greater than 460

To get all the books we can create a simple JsonPath: $.books . Now we have to add an expression in the array books. To do so we will  simple start an expression with***?*** sign and then add a filter on  the current node @ . A simple expression will look like this ?(@.pages > 460).
If we combine JsonPath with the expression we will get this: $.books[?(@.pages > 460)]
In the JsonPath Evaluator, simply enter this expression and see the results. As shown in the image below

The result will be all the books with page numbers greater than 460. Here is the result Json
[
  {
    "isbn": "9781593275846",
    "title": "Eloquent JavaScript, Second Edition",
    "subtitle": "A Modern Introduction to Programming",
    "author": "Marijn Haverbeke",
    "published": "2014-12-14T00:00:00.000Z",
    "publisher": "No Starch Press",
    "pages": 472,
    "description": "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
    "website": "https://eloquentjavascript.net/"
  },
  {
    "isbn": "9781449337711",
    "title": "Designing Evolvable Web APIs with ASP.NET",
    "subtitle": "Harnessing the Power of the Web",
    "author": "Glenn Block, et al.",
    "published": "2014-04-07T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 538,
    "description": "Design and build Web APIs for a broad range of clients—including browsers and mobile devices—that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft’s ASP.NET Web API framework. In the process, you’ll learn how design and implement a real-world Web API.",
    "website": "https://chimera.labs.oreilly.com/books/1234000001708/index.html"
  }
]

Logical operators in JsonPath
Just like any programming language, JsonPath supports all the logical operators. Below is the list of Logical  Operators that we can use to create expressions. Every logical operator  is discussed in detail below.

 

Operator
 
Description

 


==
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.



Try all the above examples and also try to create more expressions based on your needs. This way you will learn more about the JsonPath expressions.
Equals to (==) operator in JsonPath
As the name suggests the operator checks if the left-hand side is  equal to the right-hand side. Let us find out all the books that have  352 pages. Here is the JsonPath
JsonPath:  $.books[?(@.pages == 352)]
Result will be:
[
  {
    "isbn": "9781593277574",
    "title": "Understanding ECMAScript 6",
    "subtitle": "The Definitive Guide for JavaScript Developers",
    "author": "Nicholas C. Zakas",
    "published": "2016-09-03T00:00:00.000Z",
    "publisher": "No Starch Press",
    "pages": 352,
    "description": "ECMAScript 6 represents the biggest update to the core of JavaScript in the history of the language. In Understanding ECMAScript 6, expert developer Nicholas C. Zakas provides a complete guide to the object types, syntax, and other exciting changes that ECMAScript 6 brings to JavaScript.",
    "website": "https://leanpub.com/understandinges6/read"
  }
]

Not equal to (!=) operator in JsonPath
When we want to exclude a particular set of  values based on a condition we use the not equal to operator. Let us  just invert the example above and find all the books that have page numbers not equal to 352.
JsonPath: $.books[?(@.pages != 352)]
Result will be:
[
  {
    "isbn": "9781593275846",
    "title": "Eloquent JavaScript, Second Edition",
    "subtitle": "A Modern Introduction to Programming",
    "author": "Marijn Haverbeke",
    "published": "2014-12-14T00:00:00.000Z",
    "publisher": "No Starch Press",
    "pages": 472,
    "description": "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
    "website": "https://eloquentjavascript.net/"
  },
  {
    "isbn": "9781449331818",
    "title": "Learning JavaScript Design Patterns",
    "subtitle": "A JavaScript and jQuery Developer's Guide",
    "author": "Addy Osmani",
    "published": "2012-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "With Learning JavaScript Design Patterns, you'll learn how to write beautiful, structured, and maintainable JavaScript by applying classical and modern design patterns to the language. If you want to keep your code efficient, more manageable, and up-to-date with the latest best practices, this book is for you.",
    "website": "https://www.addyosmani.com/resources/essentialjsdesignpatterns/book/"
  },
  {
    "isbn": "9781449365035",
    "title": "Speaking JavaScript",
    "subtitle": "An In-Depth Guide for Programmers",
    "author": "Axel Rauschmayer",
    "published": "2014-02-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 460,
    "description": "Like it or not, JavaScript is everywhere these days-from browser to server to mobile-and now you, too, need to learn the language or dive deeper than you have. This concise book guides you into and through JavaScript, written by a veteran programmer who once found himself in the same position.",
    "website": "https://speakingjs.com/"
  },
  {
    "isbn": "9781491950296",
    "title": "Programming JavaScript Applications",
    "subtitle": "Robust Web Architecture with Node, HTML5, and Modern JS Libraries",
    "author": "Eric Elliott",
    "published": "2014-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "Take advantage of JavaScript's power to build robust web-scale or enterprise applications that are easy to extend and maintain. By applying the design patterns outlined in this practical book, experienced JavaScript developers will learn how to write flexible and resilient code that's easier-yes, easier-to work with as your code base grows.",
    "website": "https://chimera.labs.oreilly.com/books/1234000000262/index.html"
  },
  {
    "isbn": "9781491904244",
    "title": "You Don't Know JS",
    "subtitle": "ES6 & Beyond",
    "author": "Kyle Simpson",
    "published": "2015-12-27T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 278,
    "description": "No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the 'You Don’t Know JS' series, this compact guide focuses on new features available in ECMAScript 6 (ES6), the latest version of the standard upon which JavaScript is built.",
    "website": "https://github.com/getify/You-Dont-Know-JS/tree/master/es6+&+beyond"
  },
  {
    "isbn": "9781449325862",
    "title": "Git Pocket Guide",
    "subtitle": "A Working Introduction",
    "author": "Richard E. Silverman",
    "published": "2013-08-02T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 234,
    "description": "This pocket guide is the perfect on-the-job companion to Git, the distributed version control system. It provides a compact, readable introduction to Git for new users, as well as a reference to common commands and procedures for those of you with Git experience.",
    "website": "https://chimera.labs.oreilly.com/books/1230000000561/index.html"
  },
  {
    "isbn": "9781449337711",
    "title": "Designing Evolvable Web APIs with ASP.NET",
    "subtitle": "Harnessing the Power of the Web",
    "author": "Glenn Block, et al.",
    "published": "2014-04-07T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 538,
    "description": "Design and build Web APIs for a broad range of clients—including browsers and mobile devices—that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft’s ASP.NET Web API framework. In the process, you’ll learn how design and implement a real-world Web API.",
    "website": "https://chimera.labs.oreilly.com/books/1234000001708/index.html"
  }
]

Less than ( < ) operator in JsonPath
Less than operator, as the name suggests will return all the values  that are less than the value given on the right. Let us find out all the  books with pages less than 352.
JsonPath: $.books[?(@.pages < 352)]
Result will be:
[
  {
    "isbn": "9781449331818",
    "title": "Learning JavaScript Design Patterns",
    "subtitle": "A JavaScript and jQuery Developer's Guide",
    "author": "Addy Osmani",
    "published": "2012-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "With Learning JavaScript Design Patterns, you'll learn how to write beautiful, structured, and maintainable JavaScript by applying classical and modern design patterns to the language. If you want to keep your code efficient, more manageable, and up-to-date with the latest best practices, this book is for you.",
    "website": "https://www.addyosmani.com/resources/essentialjsdesignpatterns/book/"
  },
  {
    "isbn": "9781491950296",
    "title": "Programming JavaScript Applications",
    "subtitle": "Robust Web Architecture with Node, HTML5, and Modern JS Libraries",
    "author": "Eric Elliott",
    "published": "2014-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "Take advantage of JavaScript's power to build robust web-scale or enterprise applications that are easy to extend and maintain. By applying the design patterns outlined in this practical book, experienced JavaScript developers will learn how to write flexible and resilient code that's easier-yes, easier-to work with as your code base grows.",
    "website": "https://chimera.labs.oreilly.com/books/1234000000262/index.html"
  },
  {
    "isbn": "9781491904244",
    "title": "You Don't Know JS",
    "subtitle": "ES6 & Beyond",
    "author": "Kyle Simpson",
    "published": "2015-12-27T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 278,
    "description": "No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the 'You Don’t Know JS' series, this compact guide focuses on new features available in ECMAScript 6 (ES6), the latest version of the standard upon which JavaScript is built.",
    "website": "https://github.com/getify/You-Dont-Know-JS/tree/master/es6+&+beyond"
  },
  {
    "isbn": "9781449325862",
    "title": "Git Pocket Guide",
    "subtitle": "A Working Introduction",
    "author": "Richard E. Silverman",
    "published": "2013-08-02T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 234,
    "description": "This pocket guide is the perfect on-the-job companion to Git, the distributed version control system. It provides a compact, readable introduction to Git for new users, as well as a reference to common commands and procedures for those of you with Git experience.",
    "website": "https://chimera.labs.oreilly.com/books/1230000000561/index.html"
  }
]

Less than equal to ( <= ) operator in JsonPath
This operator will let you get all the values that are less than or  equal to a given value. Let us find out all the books which have pages  less than or equal to 352.
JsonPath: $.books[?(@.pages < 352)]
Result will be:
[
  {
    "isbn": "9781449331818",
    "title": "Learning JavaScript Design Patterns",
    "subtitle": "A JavaScript and jQuery Developer's Guide",
    "author": "Addy Osmani",
    "published": "2012-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "With Learning JavaScript Design Patterns, you'll learn how to write beautiful, structured, and maintainable JavaScript by applying classical and modern design patterns to the language. If you want to keep your code efficient, more manageable, and up-to-date with the latest best practices, this book is for you.",
    "website": "https://www.addyosmani.com/resources/essentialjsdesignpatterns/book/"
  },
  {
    "isbn": "9781491950296",
    "title": "Programming JavaScript Applications",
    "subtitle": "Robust Web Architecture with Node, HTML5, and Modern JS Libraries",
    "author": "Eric Elliott",
    "published": "2014-07-01T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 254,
    "description": "Take advantage of JavaScript's power to build robust web-scale or enterprise applications that are easy to extend and maintain. By applying the design patterns outlined in this practical book, experienced JavaScript developers will learn how to write flexible and resilient code that's easier-yes, easier-to work with as your code base grows.",
    "website": "https://chimera.labs.oreilly.com/books/1234000000262/index.html"
  },
  {
    "isbn": "9781491904244",
    "title": "You Don't Know JS",
    "subtitle": "ES6 & Beyond",
    "author": "Kyle Simpson",
    "published": "2015-12-27T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 278,
    "description": "No matter how much experience you have with JavaScript, odds are you don’t fully understand the language. As part of the 'You Don’t Know JS' series, this compact guide focuses on new features available in ECMAScript 6 (ES6), the latest version of the standard upon which JavaScript is built.",
    "website": "https://github.com/getify/You-Dont-Know-JS/tree/master/es6+&+beyond"
  },
  {
    "isbn": "9781449325862",
    "title": "Git Pocket Guide",
    "subtitle": "A Working Introduction",
    "author": "Richard E. Silverman",
    "published": "2013-08-02T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 234,
    "description": "This pocket guide is the perfect on-the-job companion to Git, the distributed version control system. It provides a compact, readable introduction to Git for new users, as well as a reference to common commands and procedures for those of you with Git experience.",
    "website": "https://chimera.labs.oreilly.com/books/1230000000561/index.html"
  }
]

Greater than ( > ) operator in JsonPath
Greater than operator will let you get all the values which are  greater than the value on the left-hand side. Let us find all the books  which have pages more than 460.
JsonPath: $.books[?(@.pages > 460)]
Result will be:
[
  {
    "isbn": "9781593275846",
    "title": "Eloquent JavaScript, Second Edition",
    "subtitle": "A Modern Introduction to Programming",
    "author": "Marijn Haverbeke",
    "published": "2014-12-14T00:00:00.000Z",
    "publisher": "No Starch Press",
    "pages": 472,
    "description": "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
    "website": "https://eloquentjavascript.net/"
  },
  {
    "isbn": "9781449337711",
    "title": "Designing Evolvable Web APIs with ASP.NET",
    "subtitle": "Harnessing the Power of the Web",
    "author": "Glenn Block, et al.",
    "published": "2014-04-07T00:00:00.000Z",
    "publisher": "O'Reilly Media",
    "pages": 538,
    "description": "Design and build Web APIs for a broad range of clients—including browsers and mobile devices—that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft’s ASP.NET Web API framework. In the process, you’ll learn how design and implement a real-world Web API.",
    "website": "https://chimera.labs.oreilly.com/books/1234000001708/index.html"
  }
]

Greater than equal to ( >= ) operator in JsonPath
Greater than equal will let you get all the values that are equal to  or greater than value on the right-hand side. Let's get all the books  with pages either greater than or equal to 460
JsonPath: $.books[?(@.pages >= 460)]
Result will be:
[
   {
      "isbn" : "9781593275846",
      "title" : "Eloquent JavaScript, Second Edition",
      "subtitle" : "A Modern Introduction to Programming",
      "author" : "Marijn Haverbeke",
      "published" : "2014-12-14T00:00:00.000Z",
      "publisher" : "No Starch Press",
      "pages" : 472,
      "description" : "JavaScript lies at the heart of almost every modern web application, from social apps to the newest browser-based games. Though simple for beginners to pick up and play with, JavaScript is a flexible, complex language that you can use to build full-scale applications.",
      "website" : "https://eloquentjavascript.net/"
   },
   {
      "isbn" : "9781449365035",
      "title" : "Speaking JavaScript",
      "subtitle" : "An In-Depth Guide for Programmers",
      "author" : "Axel Rauschmayer",
      "published" : "2014-02-01T00:00:00.000Z",
      "publisher" : "O'Reilly Media",
      "pages" : 460,
      "description" : "Like it or not, JavaScript is everywhere these days-from browser to server to mobile-and now you, too, need to learn the language or dive deeper than you have. This concise book guides you into and through JavaScript, written by a veteran programmer who once found himself in the same position.",
      "website" : "https://speakingjs.com/"
   },
   {
      "isbn" : "9781449337711",
      "title" : "Designing Evolvable Web APIs with ASP.NET",
      "subtitle" : "Harnessing the Power of the Web",
      "author" : "Glenn Block, et al.",
      "published" : "2014-04-07T00:00:00.000Z",
      "publisher" : "O'Reilly Media",
      "pages" : 538,
      "description" : "Design and build Web APIs for a broad range of clients\u2014including browsers and mobile devices\u2014that can adapt to change over time. This practical, hands-on guide takes you through the theory and tools you need to build evolvable HTTP services with Microsoft\u2019s ASP.NET Web API framework. In the process, you\u2019ll learn how design and implement a real-world Web API.",
      "website" : "https://chimera.labs.oreilly.com/books/1234000001708/index.html"
   }
]


In the next chapters, we will use JsonPath in Rest-Assured and see how we can write efficient validations.