问题
In the Json string given below, I want to find all elements in which category = m AND the "middle" array contains elements which match this condition - the element's "middle" array has objects whose itemType = Executable.
I would like to use jsonpath to get the desired objects. I prefer to not use jmespath because it can be too complex for my purpose. But, I am new to jsonpath and I am not able to figure out the json query from online tutorials which are too trivial or basic. I wonder if its better to use a programming language instead to get the data I need. Please advise.
So far, I was able to only extract elements in which category = m by using this jsonpath query $.[?(@.category=="m")]. How do I do the remaining part ?
Json : Overview - Every object has a "content" object. Each content object generally has a start, middle and end array besides other fields. Middle arrays can have multiple content objects inside them and so on. Some of the content objects have only a middle array. I am interested in locating items in such content objects as mentioned above.
Note that this is not the actual json which I have to process. It is an imitation which has been sanitized for SO.
{
"id": "123",
"contents": {
"title": "B1",
"start": [],
"middle": [
{
"level": "1",
"contents": {
"title": "C1",
"category": "c",
"start": [],
"middle": [
{
"level": "2",
"contents": {
"title": "M1",
"category": "m",
"start": [],
"middle": [
{
"level": "3",
"contents": {
"title": "MAT1",
"middle": [
{
"itemType": "Data"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT2",
"middle": [
{
"itemType": "Executable",
"id": "exec1"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT3",
"middle": [
{
"itemType": "Data"
}
]
}
}
],
"end": []
}
},
{
"level": "2",
"contents": {
"title": "M2",
"category": "m",
"start": [],
"middle": [
{
"level": "3",
"contents": {
"title": "MAT1",
"middle": [
{
"itemType": "Data"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT2",
"middle": [
{
"itemType": "Executable",
"id": "exec2"
}
]
}
}
],
"end": []
}
}
],
"end": []
}
},
{
"level": "1",
"contents": {
"title": "C2",
"category": "c",
"start": [],
"middle": [
{
"level": "2",
"contents": {
"title": "M1",
"category": "m",
"start": [],
"middle": [
{
"level": "3",
"contents": {
"title": "MAT1",
"middle": [
{
"itemType": "Data"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT2",
"middle": [
{
"itemType": "Executable",
"id": "exec3"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT3",
"middle": [
{
"itemType": "Data"
}
]
}
}
],
"end": []
}
},
{
"level": "2",
"contents": {
"title": "M2",
"category": "m",
"start": [],
"middle": [
{
"level": "3",
"contents": {
"title": "MAT1",
"middle": [
{
"itemType": "Data"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT2",
"middle": [
{
"itemType": "Executable",
"id": "exec4"
}
]
}
},
{
"level": "3",
"contents": {
"title": "MAT3",
"middle": [
{
"itemType": "Data"
}
]
}
}
],
"end": []
}
}
],
"end": []
}
}
],
"end": []
}
}
回答1:
Context
- json with nested objects1
- jsonpath expression language
- choosing between jsonpath and jmespath (or other JSON expression engine)
Problem
- DeveMasterJoe2 wants to extract some values from nested JSON
Discussion
- There are lots of implementations of jsonpath out there, and they do not all support the same features
- The structure and normalization of the source JSON is going to influence how easily this can be done with pure jsonpath
- In choosing a JSON expression engine, one has to weigh multiple factors
- how consistent are the implementations across languages?
- how many choices are there within a given language?
- how clear is the specification?
- how many examples, unit-tests or tutorials are available?
- who is supporting it?
Example solution using Python and jsonpath-ng
- Here is an example solution using python 3.7 and jsonpath-ng
- This example uses a mix of jsonpath and python instead of just pure jsonpath, because of the heavily-nested JSON
- I will leave it for someone else to provide an answer that relies on pure jsonpath
- Note that the source JSON arguably could stand to be cleaned up a bit
- (for example, why is there no id field attached to
itemType==Dataelements?) - (for example, why is
categorynot found on allcontentselements?) - (for example, if you expressly specify
levelwhy complicate things with heavily nested objects when you can determine depth bylevel?)
- (for example, why is there no id field attached to
This example:
## import libraries
import codecs
import json
import jsonpath_ng
from jsonpath_ng.ext import parse
##;;
## init vars
href="path/to/my/jsonfile/nested_dict.json"
json_string = codecs.open(href, 'rb', encoding='utf8').read()
json_dataroot = json.loads(json_string)
final_result = []
##;;
## init jsonpath outer-query
match = parse('$..contents.middle[*]').find(json_dataroot)
##;;
## iterate through outer-query and gather subelements
for ijj,item in enumerate(match):
## restrict to desired category == 'm'
if(match[ijj].value.get('contents',{}).get('category','') == 'm'):
## extract out desired subelements
json_datafrag001 = [item.get('contents',{}).get('middle',{})[0]
for item in match[ijj].value.get('contents',{}).get('middle',{})
]
match001 = parse("$[?(@.itemType=='Executable')]").find(json_datafrag001)
final_result.extend(list(match001[ikk].value for ikk,item in enumerate(match001)))
pass
##;;
## show final result
vout = json.dumps(final_result, sort_keys=True,indent=4, separators=(',', ': '))
print(vout)
##;;
... produces this result ...
[
{
"id": "exec1",
"itemType": "Executable"
},
{
"id": "exec2",
"itemType": "Executable"
},
{
"id": "exec3",
"itemType": "Executable"
},
{
"id": "exec4",
"itemType": "Executable"
}
]
1 (aka dictionary, associative-array, hash)
来源：https://stackoverflow.com/questions/59206765/jsonpath-extract-object-meeting-multiple-criteria