How to insert a attribute with a dynamic value in many object or add an element dynamically in many array?

问题

I want to add an attribute in many object(situated in an array) and this value will be get dynamically. I use the JSON below, and I already made a query to extract what I want. We will start with th result of this query.

First my entire JSON:

[  
   {  
      "Nature":"lol",
      "EV":"lol",
      "Moves":[  
         {  
"Move":"OHKOmove",
            "Max":100,
            "Min":15
         },
         {  
"Move":"cacaz",
            "Max":35,
            "Min":20
         }
      ]
   },
   {  
      "Nature":"loi",
      "EV":"lal",
      "Moves":[  
         {  
"Move":"caca1",
            "Max":100,
            "Min":3
         },
{  
"Move":"caca2",
            "Max":100,
            "Min":3
         }
      ]
   },
   {  
      "Nature":"loi2",
      "EV":"lal",
      "Moves":[  
         {  
"Move":"caca1",
            "Max":100,
            "Min":3
         },
{  
"Move":"caca2",
            "Max":100,
            "Min":3
         },
{  
"Move":"caca3",
            "Max":100,
            "Min":3
         }
      ]
   },
   {  
      "Nature":"loi3",
      "EV":"lil",
      "Moves":[  
         {  
"Move":"caca1",
            "Max":100,
            "Min":3
         },
{  
"Move":"caca2",
            "Max":100,
            "Min":3
         },
{  
"Move":"caca3",
            "Max":100,
            "Min":3
         }
      ]
   }
]

Then my query: [?(length(Moves[?Max == `100`]) > `1`)].{Nature: Nature, EV: EV, Moves: Moves[?Max == `100`].Move, MovesCount: length(Moves[?Max == `100`].Move)} | [@,{MaxMouvCount: max_by(@, &MovesCount).MovesCount}][]

And the result of my query give this:

JSON Format Example 1

[
 {
   "Nature": "loi",
   "EV": "lal",
   "Moves": [
     "caca1",
     "caca2"
   ],
   "MovesCount": 2
 },
 {
   "Nature": "loi2",
   "EV": "lal",
   "Moves": [
     "caca1",
     "caca2",
     "caca3"
   ],
   "MovesCount": 3
 },
 {
   "Nature": "loi3",
   "EV": "lil",
   "Moves": [
     "caca1",
     "caca2",
     "caca3"
   ],
   "MovesCount": 3
 },
 {
   "MaxMouvCount": 3
 }
]

The idea is to put the attribute "MaxMouvCount": 3 on each objects in the array and then delete it from the array to give a result like this:

JSON Format Example 2

[
  {
    "Nature": "loi",
    "EV": "lal",
    "Moves": [
      "caca1",
      "caca2"
    ],
    "MovesCount": 2,
    "MaxMouvCount": 3
  },
  {
    "Nature": "loi2",
    "EV": "lal",
    "Moves": [
      "caca1",
      "caca2",
      "caca3"
    ],
    "MovesCount": 3,
    "MaxMouvCount": 3
  },
  {
    "Nature": "loi3",
    "EV": "lil",
    "Moves": [
      "caca1",
      "caca2",
      "caca3"
    ],
    "MovesCount": 3,
    "MaxMouvCount": 3
  }
]

In the title I talk about array, in fact with .* after my query I can transform the object in array and maybe put more easier the value in each array(matching with objects) and retransform array into object with object constructor. But I don't know how to do it. Can you help me please or tell me at least if it's possible.

PS: I use only JMESPath so I don't want an answer with any other language which contains JMESPath code(like javascript(in my case) or python or something else)

回答1:

Quick Answer (TL;DR)

Usually it is easy to painlessly transform JSON with JMESPath
- One pain-free key is to utilize JSON structures that are specifically normalized for optimal use with JMESPath
- One pain-free key is knowing when to use dictionary (aka objects // associative-arrays // mappings) name-value pairs in your JSON to make all parts of the JSON capable of unambiguous reference
Unfortunately, the goal in this specific question is not doable with standard JMESPath, because JMESPath lacks a token to refer to the JSON data root in the current-node context

Detailed Answer

Context

JMESPath query language
python 3.x using JMESPath 0.9.4 [but any JMESPath engine will do]

Problem

Scenario:
- DeveloperSObosskay972 wishes to transform JSON data from one representation to another
- DeveloperSObosskay972 wants to rely solely on JMESPath expressions to complete the transformation
- DeveloperSObosskay972 wants to refer to one part of the JSON structure in another part, to allow for dynamic cross-referencing of the datastructure

Attempt 01 (not what we really want)

the "almost" solution that is not quite what we want
this code ...

import jmespath
vdata001aa = """<<json.load(JSON Format Example 1)>>"""
vresult = jmespath.compile('@|[*].{"Nature":@.Nature,"EV":@.EV,"Moves":@.Moves,"MovesCount":@.MovesCount,"MaxMouvCount":`3`}').search(vdata001aa)
pprint.pprint(vresult)

produces this result ...

[{'EV': 'lal',
  'MaxMouvCount': 3,
  'Moves': ['caca1', 'caca2'],
  'MovesCount': 2,
  'Nature': 'loi'},
 {'EV': 'lal',
  'MaxMouvCount': 3,
  'Moves': ['caca1', 'caca2', 'caca3'],
  'MovesCount': 3,
  'Nature': 'loi2'},
 {'EV': 'lil',
  'MaxMouvCount': 3,
  'Moves': ['caca1', 'caca2', 'caca3'],
  'MovesCount': 3,
  'Nature': 'loi3'},
 {'EV': None,
  'MaxMouvCount': 3,
  'Moves': None,
  'MovesCount': None,
  'Nature': None}]

This is not what we want, because:
- we had to hardwire the value 3 for MaxMouvCount which is technically "cheating"
  - it's cheating because we want a dynamic value, not a hard-wired value
- this produces a superfluous element where every value except MaxMouvCount is null (python happens to call this None)
- we only wanted three elements, not four

Attempt 02 (not what we really want)

The reason why Attempt 01 does not work well is because the original JSON stucture is not well-normalized for JMESPath
In order to address this, we add dictionary name-value pairs to the original data
With this approach, we make every element of the JSON data a value attached to a dictionary key (aka javascript object name-value pairs)
- Here we use the term dictionary which is known in other contexts as object or hash or associative array or mapping
- We don't care about the terminology, so much as the ability to refer to all parts of the top-level JSON as name-value pairs

Attempt 02 // Part 1 (reformat JSON Format Example 1)

reformat your original JSON JSON Format Example 1 so it looks like this instead
this reformatted JSON will make all parts of your data unambiguously addressible

{
"jsontop": {
    "settings_info": {
      "MaxMouvCount": 3
    },
    "nature_table": [
     {
       "Nature": "loi",
       "EV": "lal",
       "Moves": [
         "caca1",
         "caca2"
       ],
       "MovesCount": 2
     },
     {
       "Nature": "loi2",
       "EV": "lal",
       "Moves": [
         "caca1",
         "caca2",
         "caca3"
       ],
       "MovesCount": 3
     },
     {
       "Nature": "loi3",
       "EV": "lil",
       "Moves": [
         "caca1",
         "caca2",
         "caca3"
       ],
       "MovesCount": 3
     }
    ]
}

Attempt 02 // Part 2 (run the pain-free JMESPath query to get what you want)

this code ...

import jmespath
vdata001aa  = """<<json.load(**RE-NORMALIZED** JSON Format Example 1)>>"""
vresult     = jmespath.compile('@|jsontop.nature_table[*].{"Nature":@.Nature,"EV":@.EV,"Moves":@.Moves,"MovesCount":@.MovesCount,"MaxMouvCount":jsontop.settings_info.MaxMouvCount}').search(vdata001aa)
pprint.pprint(vresult)
pass

produces this result ...

[{'EV': 'lal',
  'MaxMouvCount': None,
  'Moves': ['caca1', 'caca2'],
  'MovesCount': 2,
  'Nature': 'loi'},
 {'EV': 'lal',
  'MaxMouvCount': None,
  'Moves': ['caca1', 'caca2', 'caca3'],
  'MovesCount': 3,
  'Nature': 'loi2'},
 {'EV': 'lil',
  'MaxMouvCount': None,
  'Moves': ['caca1', 'caca2', 'caca3'],
  'MovesCount': 3,
  'Nature': 'loi3'}]

this is not what we want, because we get None (aka null) where we expected 3

Explanation

Attempt 02 would have worked, if JMESPath supported a token to refer to the JSON root object
An alternate query which would work is (if for example, the dollar-sign character worked as a reference to the JSON data root)

import jmespath
vdata001aa  = """<<json.load(**RE-NORMALIZED** JSON Format Example 1)>>"""
vresult     = jmespath.compile('@|jsontop.nature_table[*].{"Nature":@.Nature,"EV":@.EV,"Moves":@.Moves,"MovesCount":@.MovesCount,"MaxMouvCount":$.jsontop.settings_info.MaxMouvCount}').search(vdata001aa)
pprint.pprint(vresult)
pass

There is actually a project on GitHub that addresses this limitation of JMESPath
- https://github.com/grofers/go-codon/wiki/Jmespath-extensions#3-added--to-refer-to-root-node

Conclusion

Attempt 01 and Attempt 02 show that the current (stable) version of JMESPath does not quite have the ability to meet the requirement
You will have to break out of JMESPath to get the desired dynamic value from your JSON and populate the reformatted data
Alternatively, you will have to add an extension to JMESPath itself, which is arguably less desirable than using the functionality of the hosting language

来源：https://stackoverflow.com/questions/57223274/how-to-insert-a-attribute-with-a-dynamic-value-in-many-object-or-add-an-element

标签

jmespath