如何仅使用jsonpath将数组转换为子集？

Question

I'd like to use jsonpath to transform an array with 3 elements to just 2 elements.

Given this object:

var _base = {
    myArray: [{ item: 1, value: "first" }, { item: 2, value: "second" }, { item: 3, value: "third" }]
}

I'd like to use jsonpath-object transform to transform the object into:

var _newBase = {
    myArray: [{ newItem: 2, newValue: "second" }, { newItem: 3, newValue: "third" }]
}

I understand I could do this with a simple slice call and some object manipulation, but I have complex, variable objects that I'm transforming at runtime, so jsonpath is the requirement.

I'm able to use the below:

var transform = require('jsonpath-object-transform');
var template = { ["$.myArray", { "newItem": "$..item", "newValue": "$..value" }] }
transform(_base, _template) //emits the below

Which emits:

[{ newItem: 1, newValue: "one" }, { newItem: 2, newValue: "second" }, { newItem: 3, newValue: "third" }]

But what I really need is the above object without its first index (so just the last two objects in the array).

Answer 1

You can use the @path syntax to ignore the first item:

var _template = {
  foo: ['$.myArray[?(@path !== "$[\'myArray\'][0]")]']
};

Returns:

{ foo: [ { item: 2, value: 'second' }, { item: 3, value: 'third' } ] }

However, it seems that jsonpath-object transform currently doesn't support mixing both @path and accessing subfields like in {["$.data", {"key": "$.value"}]} . So this leaves you with the following options:

• You can acheive what you need by using two transform operations: the first to prune out the first item, and the second to rename subfields.
• slice -ing your objects beforehand, as you suggested.
• And finally, patching the library (and submitting a pull request while you're at it!). It's probably a quick fix anyway, shouldn't be too time-consuming.