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Note (version 0.9.1 ) if your field name is like mongodb operator name (for example type, lte, lt...) and you want to place it at the end of lookup keyword mongoengine automatically prepend $ to it.To avoid this use __ at the end of your lookup keyword.The $type Query Operator and Arrays Let’s begin by revisiting arrays and queries.
It gave some very interesting insights, which was not very apparent from the documentation First we query the database for the records we need to modify. Since what we really want to do is update a value in the embedded document which is basically a list of documents, we need to traverse through the document in the embedded document.For example if your field name is A variation of this method, get_or_create() existed, but it was unsafe.It could not be made safe, because there are no transactions in mongo DB.Meanwhile, len() retrieves all the results, places them in a local cache, and finally counts them.If we compare the performance of the two operations, len() is much slower than objects.
Say, for example, you wanted to find all documents in your “address” collection where the field “first_name” is of type String.