I am using pymongo to query for all items in a region (actually it is to query for all venues in a region on a map). I used db.command(SON())
before to search in a spherical region, which can return me a dictionary and in the dictionary there is a key called results
which contains the venues. Now I need to search in a square area and I am suggested to use db.places.find
, however, this returns me a pymongo.cursor.Cursor
class and I have no idea how to extract the venue results from it.
Does anyone know whether I should convert the cursor into a dict and extract the results out, or use another method to query for items in a square region? BTW, db is pymongo.database.Database class
The codes are:
>>> import pymongo >>> db = pymongo.MongoClient(host).PSRC >>> resp = db.places.find({"loc": {"$within": {"$box": [[ll_lng,ll_lat], [ur_lng,ur_lat]]}}}) >>> for doc in resp: >>> print(doc)
I have values of ll_lng, ll_lat, ur_lng and ur_lat, use these values but it prints nothing from this codes
Manually iterating a cursor. In MongoDB, the find() method return the cursor, now to access the document we need to iterate the cursor. In the mongo shell, if the cursor is not assigned to a var keyword then the mongo shell automatically iterates the cursor up to 20 documents.
As we already discussed what is a cursor. It is basically a tool for iterating over MongoDB query result sets. This cursor instance is returned by the find() method.
Check if the Cursor object is empty or not? Approach 1: The cursor returned is an iterable, thus we can convert it into a list. If the length of the list is zero (i.e. List is empty), this implies the cursor is empty as well.
PyMongo read all data The find method selects documents in a collection or view and returns a cursor to the selected documents.
The find
method returns a Cursor
instance, which allows you to iterate over all matching documents.
To get the first document that matches the given criteria you need to use find_one
. The result of find_one
is a dictionary.
You can always use the list
constructor to return a list of all the documents in the collection but bear in mind that this will load all the data in memory and may not be what you want.
You should do that if you need to reuse the cursor and have a good reason not to use rewind()
Demo using find
:
>>> import pymongo >>> conn = pymongo.MongoClient() >>> db = conn.test #test is my database >>> col = db.spam #Here spam is my collection >>> cur = col.find() >>> cur <pymongo.cursor.Cursor object at 0xb6d447ec> >>> for doc in cur: ... print(doc) # or do something with the document ... {'a': 1, '_id': ObjectId('54ff30faadd8f30feb90268f'), 'b': 2} {'a': 1, 'c': 3, '_id': ObjectId('54ff32a2add8f30feb902690'), 'b': 2}
Demo using find_one
:
>>> col.find_one() {'a': 1, '_id': ObjectId('54ff30faadd8f30feb90268f'), 'b': 2}
Easy
import pymongo conn = pymongo.MongoClient() db = conn.test #test is my database col = db.spam #Here spam is my collection array = list(col.find()) print(array)
There you go
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