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Limit Query in MongoDB Python
Shashank Shanu
3 years ago
While working with any project, you might come
across a scenario where you wanted to retrieve only top 5 data, last 3 data or
you might want data from the middle of your dataset. Today, in this article I will
try to show you how we can do this MongoDB.
First lets us recap.
What is MongoDB?
MongoDB is
one of the widely used databases with its document stored as collections. These
documents can be compared to JSON objects. It is classified as a NoSQL database
program.
Note: MongoDB
when it is used with Python then the combination is termed as PyMongo.
MongoDB: Limit () function
The limit () function does
what its name suggests. It helps us in limiting the number of documents that
will be returned. It takes only one argument as the parameter which represents
the number signifying the number of documents that need to be returned.
Syntax of the limit function
db.COLLECTION_NAME.find().limit(NUMBER)Let try
to understand it better with the help of an example:
Example
Let suppose, we have
created a collection and inserted 5 documents into it as shown below −
# using database
use my_test_DB
#creating
collection
db.createCollection("my_sample")
data = [
... {"_id":
"101", "name": "Shyam", "age":
"27", "city": "Hyderabad"},
... {"_id":
"102", "name": "Ram", "age": 28,
"city": "Bangalore"},
... {"_id":
"103", "name": "john", "age": 26,
"city": "Mumbai"},
... {"_id":
"104", "name": "Romeo", "age": 25,
"city": "Pune"},
... {"_id":
"105", "name": "Sarmista", "age": 23,
"city": "Delhi"},
... {"_id":
"106", "name": "Rasajna", "age": 26,
"city": "Chennai"}
]
#insert data
db.my_sample.insert(data)Output:
BulkWriteResult({
"writeErrors" : [ ],
"writeConcernErrors" : [ ],
"nInserted" : 6,
"nUpserted" : 0,
"nMatched" : 0,
"nModified" : 0,
"nRemoved" : 0,
"upserted" : [ ]
})Now suppose you want to
retrieve only first 3 documents form the above-created collection. This can be
done as shown below:
db.my_sample.find().limit(3)Output:
The first three documents
are as follows:
{ "_id" : "101", "name" : "Shyam", "age" : "27", "city" : "Hyderabad" }
{ "_id" : "102", "name" : "Ram", "age" : 28, "city" : "Bangalore" }
{ "_id" : "103", "name" : "john", "age" : 26, "city" : "Mumbai" }Till now, we saw how we can limit our file in MongoDB, next lets
see how we can do it using python.
Limiting the Documents Using Python
For limiting mongo DB file using python is same as we discuss
above. Only we have to import Mongo Client from pymongo and connect and then
whatever function are available in mongo DB we can use them here also.
Lets see an example:
Example
Here, we are trying to retrieve
first three documents in a collection.
from pymongo import
MongoClient
#Create a pymongo client
mo_client = MongoClient('localhost', 27017)
#Getting the database instance
database = mo_client ['l']
#Creating a collection
collection = database ['my_Collections']
#Inserting document into a collection
data = [
{"_id": "1001",
"name": "Shyam", "age": "27",
"city": "Hyderabad"},
{"_id": "1002",
"name": "Ram", "age": "28",
"city": "Bangalore"},
{"_id": "1003",
"name": "John", "age": "26",
"city": "Mumbai"},
{"_id": "1004", "name": "Romeo",
"age": 25, "city": "Pune"},
{"_id": "1005",
"name": "Sarmista", "age": 23, "city":
"Delhi"},
{"_id": "1006",
"name": "Rasajna", "age": 26, "city":
"Chennai"}
]
result = collection.insert_many(data)
print("Data inserted ......")
#Retrieving first 3 documents using the find() and limit() methods
print("First 3 documents in the collection: ")
for i in coll.find().limit(3):
print(i)Output
Data inserted ......
First 3 documents in the collection:
{'_id': '101', 'name': 'Shyam', 'age': '27', 'city': 'Hyderabad'}
{'_id': '102', 'name': 'Ram', 'age': '28', 'city': 'Bangalore'}
{'_id': '103', 'name': 'John', 'age': '26', 'city': 'Mumbai'}From the above result,
we can observe that we are getting what we wanted i.e., first three collection
of the documents.
I hope after you enjoyed reading this
article and finally, you came to know about Limit Query in MongoDB Python.
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