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How to compare two JSON files that adhere to a schema?

I have JSON (for Ignition SCADA) that defines "tags" in the system which essentially defines a tree structure where the end tree nodes are the tags themselves with the configuration that defines them, and the sub-tree elements being folders. Each folder has a key called "tags" which holds a list of any tags or folders that are contained within them.

The most important parts of the JSON that defines a tag is its path which is made up of each "name" field in the JSON along the Folder path it lies in, similar to a filepath of a file. Elements of the path are separated by "/" e.g. for TagA below, its tag path would be "StackOverflow/FolderA/TagA".

Below is the tree in the Ignition designer:

Tags Displayed in Ignition Tag Browser GUI

Below is the JSON that represents these tags:

{
  "name": "StackOverflow",
  "tagType": "Folder",
  "tags": [
    {
      "name": "FolderA",
      "tagType": "Folder",
      "tags": [
        {
          "valueSource": "memory",
          "dataType": "Int8",
          "name": "TagA",
          "tooltip": "This is tag a",
          "value": 15,
          "tagType": "AtomicTag",
          "engUnit": "%"
        },
        {
          "valueSource": "memory",
          "dataType": "Int8",
          "name": "TagB",
          "tooltip": "This is tag b",
          "value": 98,
          "tagType": "AtomicTag",
          "engUnit": "%"
        }
      ]
    }
  ]
}

If I make changes to these tags/folders by:

  • adding a new tag, StackOverflow/FolderA/TagC
  • change value of StackOverflow/FolderA/TagA.tooltip
  • change value of StackOverflow/FolderA/TagA.value
  • delete StackOverflow/FolderA/TagB

I want to get a report of this as a list of changes that I can export into Excel, e.g. something like:

[{'tagpath': 'StackOverflow/FolderA/TagC', 'changedFrom': None, 'changedTo': 'added'},
{'tagpath': 'StackOverflow/FolderA/TagA.tooltip', 'changedFrom': 'This is tag a', 'changedTo': 'This is tag a with changes'},
{'tagpath': 'StackOverflow/FolderA/TagA.value', 'changedFrom': 15, 'changedTo': 59},
{'tagpath': 'StackOverflow/FolderA/TagB', 'changedFrom': None, 'changedTo': 'deleted'}
]

This is the changes JSON:

{
  "name": "StackOverflow",
  "tagType": "Folder",
  "tags": [
    {
      "name": "FolderA",
      "tagType": "Folder",
      "tags": [
        {
          "valueSource": "memory",
          "dataType": "Int8",
          "name": "TagC",
          "tooltip": "This is tag a with changes",
          "value": 59,
          "tagType": "AtomicTag",
          "engUnit": "%"
        },
        {
          "valueSource": "memory",
          "dataType": "Int8",
          "name": "TagA",
          "tooltip": "This is tag a with changes",
          "value": 59,
          "tagType": "AtomicTag",
          "engUnit": "%"
        }
      ]
    }
  ]
}

enter image description here

What I’m not sure of is how best to compare these two files using Python. I can pull something together using simple for loops and comparing the json manually and keeping track of differences, but I was wondering if there is a better more sophisticated way?

Tags:

2

Answers


  1. 0

    May be some packages will be useful. If you don’t want to use it, you can use iterator to instead for one by one.

    from jsondiff import diff
json1 = {
    "name": "Bob",
    "age": 10,
    "sex": "male"
}
json2 = {
    "name": "Alice",
    "age": 10,
    "sex": "female"
}

difference1 = diff(json1, json2)
difference2 = diff(json2, json1)
print(difference1)
print(difference2)

    result:
    {‘name’: ‘Alice’, ‘sex’: ‘female’}
    {‘name’: ‘Bob’, ‘sex’: ‘male’}

    I think you can use this to construct your change log.

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  2. 0

    The problem can be solved with littletree (I’m the author).

    Assuming the original and modified data are stored as a nested dict in original and modified respectively

    from littletree import Node

original_tree = Node.from_dict(original, identifier_name="name", children_name="tags")
modified_tree = Node.from_dict(modified, identifier_name="name", children_name="tags")

# Collect changes in a list
changes = []
for diff_node in original_tree.compare(modified_tree).iter_tree():
    diff_data = diff_node.data
    if not diff_data:
        continue  # Data was the same
    
    if "self" not in diff_data:
        changes.append({"tagpath": str(diff_node.path), "from": None, "to": "added"})
    elif "other" not in diff_data:
        changes.append({"tagpath": str(diff_node.path), "from": None, "to": "removed"})
    else:
        original_data, modified_data = diff_data["self"], diff_data["other"]
        for key, original_value in original_data.items():
            modified_value = modified_data[key]
            if original_value != modified_value:
                changes.append({"tagpath": f"{diff_node.path}.{key}",
                                "from": original_value,
                                "to": modified_value})

for change in changes:
    print(change)

    The result looks like this:

    {'tagpath': '/StackOverflow/FolderA/TagA.tooltip', 'from': 'This is tag a', 'to': 'This is tag a but changed'}
{'tagpath': '/StackOverflow/FolderA/TagA.value', 'from': 15, 'to': 16}
{'tagpath': '/StackOverflow/FolderA/TagB', 'from': None, 'to': 'removed'}
{'tagpath': '/StackOverflow/FolderA/TagC', 'from': None, 'to': 'added'}
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