How to modify the JSON

[renard]

Hi,

This seem to bee a promising lib for JSON parsing.

How can I modify a JSON structure given a path?

I would like to change:

{'foo': [{'baz': 1}, {'baz': 2}]}

to

{'foo': [{'baz': 3}, {'baz': 2}]}

Given a path: foo[0].baz

I tried:

>>> import jsonpath_rw
>>> json = {'foo': [{'baz': 1}, {'baz': 2}]}
>>> path = jsonpath_rw.parse(r'foo[0].baz')
>>> match = path.find(json)
>>> match
[DatumInContext(value=1, path=Fields('baz'), context=DatumInContext(value={'baz': 1}, path=<jsonpath_rw.jsonpath.Index object at 0x1095a7790>, context=DatumInContext(value=[{'baz': 1}, {'baz': 2}], path=Fields('foo'), context=DatumInContext(value={'foo': [{'baz': 1}, {'baz': 2}]}, path=This(), context=None))))]
>>> match[0].value
1
>>> match[0].value = 5
>>> json
{'foo': [{'baz': 1}, {'baz': 2}]}

I guess I missed something here.

thanks in advance.

Cheers

[renard]

Finally I end up with something like that:

import jsonpath_rw

def get_path(match):
    '''return an iterator based upon MATCH.PATH. Each item is a path component,
start from outer most item.'''
    if match.context is not None:
        for path_element in get_path(match.context):
            yield path_element
        yield str(match.path)

def update_json(json, path, value):
    '''Update JSON dictionnary PATH with VALUE. Return updated JSON'''
    try:
        first = next(path)
        # check if item is an array
        if first.startswith('[') and first.endswith(']'):
            try:
                first = int(first[1:-1])
            except ValueError:
                pass
        json[first] = update_json(json[first], path, value)
        return json
    except StopIteration:
        return value


json = {'foo': [{'baz': 1}, {'baz': 2}], 'bar': { 'just': 'a', 'dict': 'object'}}
path = jsonpath_rw.parse(r'*.just')
matches = path.find(json)

print json
for match in matches:
    full_path = '/'.join(get_path(match))
    json = update_json(json, get_path(match), full_path)
print json

{'foo': [{'baz': 1}, {'baz': 2}], 'bar': {'dict': 'object', 'just': 'a'}}
{'foo': [{'baz': 1}, {'baz': 2}], 'bar': {'dict': 'object', 'just': 'bar/just'}}

Maybe this could be a feature for jsonpath_rw.

[kennknowles]

Hello! This is a good point. It is actually where the "rw" in the name of the package comes from: read/write. But I got distracted. The intended design is immutable update:

data = ...
pattern = jsonpath_rw.parse('*.just')
new_data = pattern.update(data, lambda x: ...)
more_new_data = pattern.set(data, "some value")
even_more_new_data = pattern.contextual_update(data, lambda context, x: ...)

There are many useful ways to update:

• A function from old value to new value.
• A constant value to be set (degenerate form of the above).
• A function from old value and some context information to new value.

Pull requests welcome :-)

[ailjushkin]

@renard
@kennknowles
@gera
@iley
@hakanw

I'm also have to use such method. How can I change values using jsonpath?

[petr0ff]

Hi! Is there any progress on it? :) I'm getting Not implemented error, when trying to use jsonpath_expr.update(my_json, "some_value")

[ailjushkin]

There is a way to update json, but it is not documented and wrapped into a
function. I will post sample code little bit later.

пн, 18 янв. 2016, 15:40, petr0ff notifications@github.com:

Hi! Is there any progress on it? :) I'm getting Not implemented error,
when trying to use jsonpath_expr.update(my_json, "some_value")

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Reply to this email directly or view it on GitHub
#21 (comment)
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[petr0ff]

Nice, thanks! Actually I've tried @renard 's solution and it worked for me

[ailjushkin]

@petr0ff well, as I can see from PC now, joshbenner have implemented the normal update method (#28).

But just in case if someone could be interested, I post here my solution:

def string_to_json (self, source):
    try:
        load_input_json=json.loads(source)
    except ValueError, e:
        raise Exception("Could not parse '%s' as JSON: %s"%(source, e))
    return    load_input_json

def update_json(self, json_string, expr, value, index=0):
     load_input_json=self.string_to_json (json_string)
     matches = self._json_path_search(load_input_json, expr)
     datum_object = matches[int(index)]
     if not isinstance(datum_object, DatumInContext):
         raise Exception("Nothing found by the given json-path")
     path = datum_object.path
     if isinstance(path, Index):
         datum_object.context.value[datum_object.path.index] = value
     elif isinstance(path, Fields):
         datum_object.context.value[datum_object.path.fields[0]] = value

     return load_input_json

[cliffpracht]

@PositiveAlex, How are you using this without changing anything? I don't see _json_path_search defined anywhere. Are you inheriting another class from this?
Thanks.

[impredicative]

This allows updates with the jsonpath-ng package, but I still don't have a way to delete keys!

[namratha-bharadwaj]

Hi... I have been looking for a solution to this too
Can someone please help me with the full solution to this?
@ailjushkin what's the method definition of "_json_path_search(load_input_json, expr)"?
Is it taking the json_object and the jsonPath in string format, and returning the jsonpath_expr?
also, what are "Index" and "Fields" in lines "if isinstance(path, Index):" and "elif isinstance(path, Fields):"

[ulidtko]

Hey @kennknowles,

The intended design is immutable update:

data = ...
pattern = jsonpath_rw.parse('*.just')
new_data = pattern.update(data, lambda x: ...)
more_new_data = pattern.set(data, "some value")

This is indeed very nice, but would you care to release this functionality? It's available in master branch only; the latest release 1.4.0 lacks the code.

It's not that pip install https://github.com/kennknowles/python-jsonpath-rw doesn't work; rather, it's the "unfinished code in flux" status that's communicated by installing from master.