how to create a JSON file based on a template

marozsas · 10-26-2022, 09:17 AM

I have a JSON file that is used in a monitoring software for monitor an specific device.
I want to monitor a similar device which I don't have the JSON file.
I know everything from the new device that is needed to "fill the blanks" in the existent JSON structure.

A brute force approach would be create a script that reads the data from new device from a craft input file and output the nodes and leafs in the same JSON structure.

Before I take this path I would like to know if there is some tool that could help me in this task. For sure this "wheel" is not new, I don't want to re-invent it again.

Anyone knows about a tool that uses a JSON as template and generate another one changing the values from other source ?

any ideas ?

sundialsvcs · 10-26-2022, 11:15 AM

I strongly suggest that you should handle all JSON and XML data in the same way: with "magic encoder/decoder rings." First, decode the JSON into a data structure, then change that data structure as required. Finally, encode the data structure into a new JSON file. You never attempt to manipulate the data "as text." The encoder/decoder logic is industry-standard, common among every programming language these days that supports the file format, and known to be correct in all cases. You treat it as a "black box."

marozsas · 10-26-2022, 01:43 PM

I am not familiar with "magic encoder/decoder rings." What do you mean ? Can you elaborate, please ?
How it is your suggestion different than the approach I suggested ? I mean, reading a data in a certain structure (plain file) and output in another structure (json) ?

boughtonp · 10-26-2022, 02:28 PM

I think the English translation of what sundialsvcs is attempting to say is: Use the standard JSON library for the language of your choice.

For example, in pseudocode:

Code:

config = json.deserialize(file.read('/path/to/template.json'))
config.variable1 = 'something'
config.variable2 = [1,2,3]
config.variable4 = True
file.write('/path/to/output.json',json.serialize(config))

(There is nothing "brute force" about this approach.)

If you don't already have a chosen language, you can probably use jq, though I don't find its documentation very good.

marozsas · 10-26-2022, 03:54 PM

Quote:

Originally Posted by boughtonp

(There is nothing "brute force" about this approach.)

Yeah, my first "brute" force approach was in python, using json library and json.load to initialize a dictionary. This creates the output structure.
Then I iterate over the keys, replacing the original value from json template read before with new values from a plain file.
This mapping from new values to the equivalent key in json is hardcoded on the code, what I dislike.

So I thought someone could give me a better idea how to map the raw source data into the json output, not hardcoded in the script itself.....

I mean,

data = json.load (json_file)
....

data['key1']= 'comes from 2nd line of data file'
data['key2']= 'comes from 10th line of data file'
data['key3']= 'comes from 3rd line of data file'
...

this is why I called brute force.....this mapping style is not good, even worse if hardcoded.

sundialsvcs · 10-26-2022, 07:53 PM

"Yes, @boughtonp, that's exactly what I meant."

Virtually every programming language has a built-in capability to "encode and decode JSON," and in general AFAIK they use the same binary libraries to do the heavy lifting. This means that there is an excellent chance that they will all be "compatible with one another," so long as you treat each language's built-in facilities as "a black box." As a "magic encoder/decoder ring" that can be relied upon to work in all cases. You do not peer into how it works its magick ... you only implicitly trust that it does.

chrism01 · 10-26-2022, 11:04 PM

Well, you could put the x-ref mapping into it's own file eg transform.dat and have the program read that when it wants to translate from one file to the other.
In that case people only have to be able to edit a simple key=val list file for changes.

The program would then just read that (probably into hash), then go through the i/p file and pull out the relevant key for each entry to 'translate'.

Of course your program should use the std JSON libs to read/write the json files.

pan64 · 10-27-2022, 02:44 AM

you need to create a map file, which will tell you the details:

Code:

data['key1']= 'comes from 2nd line of data file'
data['key2']= 'comes from 10th line of data file'
data['key3']= 'comes from 3rd line of data file'

This can be translated to something like that

boughtonp · 10-27-2022, 08:06 AM

Quote:

Originally Posted by marozsas

So I thought someone could give me a better idea how to map the raw source data into the json output, not hardcoded in the script itself.....

That was merely a simple example to indicate the point.

If you want a better idea how to map the "raw source data" then provide clearer information as to what this source data actually is - from your references to "plain file" and "(2nd|3rd|10th) line of data file" it sounds like your source might be newline-delimited data?

In which case you need some form of mapping to associates line numbers to variables, or variables to line numbers.

Whether done via code or data, anything which explicitly maps variable a to value b is not brute force, because brute force is when you try every possible combination - i.e. by looping through all the variables/values and testing each one.