Develop Reference

pymongo Query Existing Collection

I have a database SensorReadings which has a collection MeterReadings this is populated using another script so the collection already exists.
I am setting up a script to query the MeterReadings collection. It looks like the following.
## Imports ##
import pymongo
## Variables ##
url = "mongodb://localhost:27017"
## getDBConnection ##
def getDBConnection():
client = pymongo.MongoClient(url)
db = client["SesnorReadings"]
collection = db["MeterReadings"]
readings = collection.find_one({})
for res in readings:
print(res)
readings is returning a None type. The exact error I get is shown below.
Traceback (most recent call last):
File "main.py", line 6, in <module>
conn = functions.getDBConnection()
File "functions.py", line 19, in getDBConnection
for res in readings:
TypeError: 'NoneType' object is not iterable
When I add an insert statement hwoever first and then query using the find_one method, it will create a new database SensorReadings with a collection MeterReadings in it.
## Imports ##
import pymongo
## Variables ##
url = "mongodb://localhost:27017"
## getDBConnection ##
def getDBConnection():
client = pymongo.MongoClient(url)
db = client["SesnorReadings"]
collection = db["MeterReadings"]
readings = collection.find_one({})
mydict = { "name": "John", "address": "Highway 37" }
x = collection.insert_one(mydict)
for res in readings:
print(res)
The above code returns:
_id
name
address
{'_id': ObjectId('5fc679dd439f1a27d0bb0c5e'), 'name': 'John', 'address': 'Highway 37'}
However in the Mongo terminal there are now two SensorReading databases. One has the correct data and one has the data I just added using the above snippet.
> show dbs
SensorReadings 0.000GB
SesnorReadings 0.000GB
admin 0.000GB
config 0.000GB
local 0.000GB
I just want to connect to the SesnorReadings database that is already created and query the MeterReadings collection in it.

find_one returns one document. Use find to get all documents.
And you have a typo in collection name as pointed out in the comments.

Python MongoDB Find One

I am trying to find by id a document in the database, but I get None. What am I doing wrong?
python:
card = mongo.db['grl'].find_one({'id': 448510476})
or:
card = mongo.db['grl'].find_one({'id': '448510476'})
document:
{"_id":{"$oid":"5f25b1d787fc4c34a7d9aabe"},
"id":{"$numberInt":"448510476"},"first_name":"Arc","last_name":"Fl"}

I'm not sure how you are initializing your database but try this:
from pymongo import MongoClient
client = MongoClient("mongodb://127.0.0.1:27017")
db = client.database #Selecting database named "database"
#find one in collection named "collection"
card = db.collection.find_one({"id": "448510476"})
print(card)

PyMongo - Setting all values in an attribute to lowercase [duplicate]

This question already has answers here:
Update MongoDB field using value of another field
(12 answers)
Closed 5 years ago.
I am cleaning a dataset, and have a field gender. In this field, there are entries such as Male, male, and MALE. To resolve this, I am trying to update my MongoDB database using pymongo.
In the database, the Gender attribute is Gender (which a capital G at the front)
My code currently looks like this:
import pymongo
from pymongo import MongoClient
db_info = {
'db_name': 'MentalHealth',
'collection_name': 'MentalHealth',
}
if __name__ == "__main__":
mongo_client = MongoClient()
mongo_db = mongo_client[db_info['db_name']]
mongo_collection = mongo_db[db_info['collection_name']]
#normalize to lowercase
mongo_collection.aggregate([{ '$project': { 'Gender':{ '$toLower':"$Gender"}}}])
The code runs without issue, but the database is not updating, and I am unsure what is the error with the code. Any help would be greatly appreciated. Thank you!!!

Mongodb aggregation operations process data records and return computed results. It can't update any collection. you can update the same like this
db.mongo_collection.find({}).forEach(function(doc) {
db.mongo_collection.update(
{ "_id": doc._id },
{ "$set": { "Gender": doc.Gender.toUpperCase() } }
);
});

You are using aggregate query which will return you the result with all Gender fields cast to lower case. If you wish to update the value for a field you have to use update query.
Since you are using pymongo to query your documents your code should be like this
import pymongo
from pymongo import MongoClient
from bson.objectid import ObjectId
db_info = {
'db_name': 'MentalHealth',
'collection_name': 'MentalHealth'
}
if __name__ == "__main__":
mongo_client = MongoClient()
mongo_db = mongo_client[db_info['db_name']]
mongo_collection = mongo_db[db_info['collection_name']]
for doc in mongo_collection.find(no_cursor_timeout=True):
pk = ObjectId(str(doc.get("_id")))
g = doc.get('Gender')
if g:
g = g.lower()
mongo_collection.update({"_id": pk}, {"$set":{"Gender":g}})

The aggregation framework you’re using only performs queries. To actually perform writes, you need to use a $out stage to dump the results into the collection.
If you select an existing collection, that collection is replaced atomically as described in https://docs.mongodb.com/manual/reference/operator/aggregation/out/#pipe._S_out
Another option is to use an update operation to update just the documents with incorrect case.

Pymongo $in Query Not Working

Seeing some strange behavior in Pymongo $in query. Looking for records that meet the following query:
speciesCollection.find({"SPCOMNAME":{"$in":['paddlefish','lake sturgeon']}})
The query returns no records.
If I change it to find_one the it works returning the last value for Lake Sturgeon. The field is a text filed with one vaule. So I am looking for records that match paddlefish or Lake Sturgeon.
It works fine in Mongo Shell like this:
speciesCollection.find({SPCOMNAME:{$in: ['paddlefish','lake strugeon']}},{_id:0})
Here is the result from shell
{ "SPECIES_ID" : 1, "SPECIES_AB" : "LKS", "SPCOMNAME" : "lake sturgeon", "SP_SCINAME" : "Acipenser fulvescens
{ "SPECIES_ID" : 101, "SPECIES_AB" : "PAH", "SPCOMNAME" : "paddlefish", "SP_SCINAME" : "Polyodon spathula" }
Am I missing something here?

I think you have a typo or some other error in your program as I just did a test with your sample data and query and it works - see the GIF
Below is my test code which connects to the database called so and the collection speciesCollection, maybe you find the error in yours with it
import pymongo
client = pymongo.MongoClient('dockerhostlinux1', 30000)
db = client.so
coll = db.speciesCollection
result = coll.find({"SPCOMNAME":{"$in":['paddlefish','lake sturgeon']}})
for doc in result:
print(doc)

Get all documents of a collection using Pymongo

I want to write a function to return all the documents contained in mycollection in mongodb
from pymongo import MongoClient
if __name__ == '__main__':
client = MongoClient("localhost", 27017, maxPoolSize=50)
db=client.mydatabase
collection=db['mycollection']
cursor = collection.find({})
for document in cursor:
print(document)
However, the function returns: Process finished with exit code 0

Here is the sample code which works fine when you run from command prompt.
from pymongo import MongoClient
if __name__ == '__main__':
client = MongoClient("localhost", 27017, maxPoolSize=50)
db = client.localhost
collection = db['chain']
cursor = collection.find({})
for document in cursor:
print(document)
Please check the collection name.

pymongo creates a cursor. Hence you'll get the object 'under' the cursor. To get all objects in general try:
list(db.collection.find({}))
This will force the cursor to iterate over each object and put it in a list()
Have fun...

I think this will work fine in your program.
cursor = db.mycollection # choosing the collection you need
for document in cursor.find():
print (document)

it works fine for me,try checking the exact database name and collection name.
and try changing from db=client.mydatabase to db=client['mydatabase'] .
If your database name is such that using attribute style access won’t work (like test-database), you can use dictionary style access instead.
source !