MongoDB InvalidDocument: Cannot encode object

I got this error when running a query

db.collection.find({'attr': {'$gte': 20}})

and some records in collection had a non-numeric value for attr.

Finally I figured it out. The problem was not with encoding. It was with the structure of the documents.

Because i went off on the standard MongoPipeline example which does not deal with nested scrapy items.

What i am doing is: BlogItem: "url" ... comments = [CommentItem]

So my BlogItem has a list of CommentItems. Now the problem came here, for persisting the object in the database i do:

self.db[self.collection_name].insert(dict(item))

So here i am parsing the BlogItem to a dict. But i am not parsing the list of CommentItems. And because the traceback displays the CommentItem kind of like a dict, It did not occur to me that the problematic object is not a dict!

So finally the the way to fix this problem is to change the line when appending the comment to the comment list as such:

item['comments'].append(dict(comment))

Now MongoDB considers it as a valid document.

Lastly, for the last part where i ask why i am getting a exception on the python console and not in the script.

The reason is because i was working on the python console, which only supports ascii. And thus the error.