I’m attempting to create a web service using MongoDB and Flask (using the pymongo driver). A query to the database returns documents with the “_id” field included, of course. I don’t want to send this to the client, so how do I remove it?
Here’s a Flask route:
@app.route('/theobjects') def index(): objects = db.collection.find() return str(json.dumps({'results': list(objects)}, default = json_util.default, indent = 4))
This returns:
{ "results": [ { "whatever": { "field1": "value", "field2": "value", }, "whatever2": { "field3": "value" }, ... "_id": { "$oid": "..." }, ... } ]}
I thought it was a dictionary and I could just delete the element before returning it:
del objects['_id']
But that returns a TypeError:
TypeError: 'Cursor' object does not support item deletion
So it isn’t a dictionary, but something I have to iterate over with each result as a dictionary. So I try to do that with this code:
for object in objects: del object['_id']
Each object dictionary looks the way I’d like it to now, but the objects cursor is empty. So I try to create a new dictionary and after deleting _id from each, add to a new dictionary that Flask will return:
new_object = {} for object in objects: for key, item in objects.items(): if key == '_id': del object['_id'] new_object.update(object)
This just returns a dictionary with the first-level keys and nothing else.
So this is sort of a standard nested dictionaries problem, but I’m also shocked that MongoDB doesn’t have a way to easily deal with this.
The MongoDB documentation explains that you can exclude _id with
{ _id : 0 }
But that does nothing with pymongo. The Pymongo documentation explains that you can list the fields you want returned, but “(“_id” will always be included)”. Seriously? Is there no way around this? Is there something simple and stupid that I’m overlooking here?
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Answer
To exclude the _id
field in a find query in pymongo, you can use:
db.collection.find({}, {'_id': False})
The documentation is somewhat missleading on this as it says the _id
field is always included. But you can exclude it like shown above.