Query nested JSON document in MongoDB collection using Python

Question

I have a MongoDB collection containing multiple documents. A document looks like this:

{
    'name': 'sys',
    'type': 'system',
    'path': 'sys',
    'children': [{
        'name': 'folder1',
        'type': 'folder',
        'path': 'sys/folder1',
        'children': [{
            'name': 'folder2',
            'type': 'folder',
            'path': 'sys/folder1/folder2',
            'children': [{
                'name': 'textf1.txt',
                'type': 'file',
                'path': 'sys/folder1/folder2/textf1.txt',
                'children': ['abc', 'def']
            }, {
                'name': 'textf2.txt',
                'type': 'file',
                'path': 'sys/folder1/folder2/textf2.txt',
                'children': ['a', 'b', 'c']
            }]
        }, {
            'name': 'text1.txt',
            'type': 'file',
            'path': 'sys/folder1/text1.txt',
            'children': ['aaa', 'bbb', 'ccc']
        }]
    }],
    '_id': ObjectId('5d1211ead866fc19ccdf0c77')
}

There are other documents containing similar structure. How can I query this collection to find part of one document among multiple documents where path matches sys/folder1/text1.txt?

My desired output would be:

{
   'name': 'text1.txt',
   'type': 'file',
   'path': 'sys/folder1/text1.txt',
   'children': ['aaa', 'bbb', 'ccc']
 }

EDIT: What I have come up with so far is this. My Flask endpoint:

class ExecuteQuery(Resource):
    def get(self, collection_name):
        result_list = []  # List to store query results
        query_list = []  # List to store the incoming queries
        for k, v in request.json.items():
            query_list.append({k: v})  # Store query items in list
        cursor = mongo.db[collection_name].find(*query_list)  # Execute query
        for document in cursor:
            encoded_data = JSONEncoder().encode(document)  # Encode the query results to String
            result_list.append(json.loads(encoded_data))  # Update dict by iterating over Documents
        return result_list  # Return query result to client

My client side:

request = {"name": "sys"}
response = requests.get(url, json=request, headers=headers) 
print(response.text)

This gives me the entire document but I cannot extract a specific part of the document by matching the path.

different matter: you should sanitize the user input

Markus Rother
– Markus Rother

2019-06-30 20:07:15 +00:00
Commented Jun 30, 2019 at 20:07 — Markus Rother
– Markus Rother, Commented Jun 30, 2019 at 20:07

Markus Rother · Accepted Answer · 2019-06-30 20:51:30Z

2

I don't think mongodb supports recursive or deep queries within a document (neither recursive $unwind). What it does provide however, are recursive queries across documents referencing another, i.e. aggregating elements from a graph ($graphLookup).

This answer explains pretty well, what you need to do to query a tree.

Although it does not directly address your problem, you may want to reevaluate your data structure. It certainly is intuitive, but updates can be painful -- as well as queries for nested elements, as you just noticed.

Since $graphLookup allows you to create a view equal to your current document, I cannot think of any advantages the explicitly nested structure has over one document per path. There will be a slight performance loss for reading and writing the entire tree, but with proper indexing it should be ok.

answered Jun 30, 2019 at 20:51

Markus Rother

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2 Comments

hw-135 Over a year ago

Are you sure that nested documents cannot be queried? I found this: stackoverflow.com/questions/24294273/… and this: stackoverflow.com/questions/3985214/… which elements in a nested JSON. Maybe my understanding is not right?

Markus Rother Over a year ago

Nested documents can be queried, but not in arbitrary depth.

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