JSON-Path Combining Expression With Index - json

Question

Given the following sample JSON where we will not always know the order...
{
"contacts": [
{
"id": 287997,
"type": "P",
"relationship": "Mother",
"firstName": "Sara",
"lastName": "Johnson"
},
{
"id": 300982,
"type": "EC",
"relationship": "Aunt",
"firstName": "Janet",
"lastName": "Smith"
},
{
"id": 287200,
"type": "P",
"relationship": "Father",
"firstName": "William",
"lastName": "Johnson"
},
{
"id": 287997,
"type": "EC",
"relationship": "Friend",
"firstName": "Harold",
"lastName": "Johnson"
}
]
}
I want to retrieve the first contact which is of type 'EC'. The following retrieves all 'EC' type contacts just fine...
$.contacts[?(#.type == 'EC')]
But, I want only the first EC contact. I tried...
$.contacts[?(#.type == 'EC')][0]
But this did not work. I tried a few other variations with no luck. I would like to be able to achieve this without going outside of the JSON-Path approach if possible.
I know I can combine expressions like this...
$.contacts[?(#.type == 'EC' && #.firstName == 'Janet')]
But, I need to get the first contact that matches the 'EC' expression. So, after the 'EC' expression is evaluated, get the first of the filtered contacts.
I appreciate any help I can get! Thanks!

Answer 1

Kevin - yesterday I released a JS-lib I've been working on (DefiantJS) that solves your problem exactly the way you want it, and with the standardised XPath instead of JSONPath. At this page, there is a tool I've written XPath evaluator.
http://www.defiantjs.com/#xpath_evaluator
By clicking "Edit", I have pasted your JSON structure, and clicked "Edit" again (so that the structure is parsed by the tool). Now, entering the XPath below will filter the selection you want:
//contacts[./type="EC"][1]
To put this in Javascript code:
var obj = {
"contacts": [
{
"id": 287997,
"type": "P",
"relationship": "Mother",
"firstName": "Sara",
"lastName": "Johnson"
},
{
"id": 300982,
"type": "EC",
"relationship": "Aunt",
"firstName": "Janet",
"lastName": "Smith"
},
{
"id": 287200,
"type": "P",
"relationship": "Father",
"firstName": "William",
"lastName": "Johnson"
},
{
"id": 287997,
"type": "EC",
"relationship": "Friend",
"firstName": "Harold",
"lastName": "Johnson"
}
]
};
var sel = JSON.search(obj, '//contacts[./type="EC"][1]');
// sel[0] will contain your filtered object
DefiantJS extends the global object with a new method; "search". Since the function "search" always returns an array of matching elements, the handle to your selection is "sel[0]". Another Xpath for selecting contacts with the lastName "Johnson" is:
//contacts[./lastName="Johnson"]
The XPath evaluator tool have example XPath as well - which is meant to ease in developers not familiar with XPath. The source code of DefiantJS can be found at Github:
https://github.com/hbi99/defiant.js