Limit, MongoDB

A MongoDB query may return many results—more than we need. With a limit() call on the cursor returned by find() we can reduce the number of results.

Often in programs we want to display just 10 or 20 results. A limit is ideal for restricting the number of returns for a screen of information.

Example program

This program uses some MongoClient code to set up an "animals" collection in a "veterinarian" database. Everyone loves animals (although not cleaning up after them).

Here We invoke the find() method to find dogs in our tiny example collection. There are 3 dogs present.

Tip We use a limit() call on our cursor to restrict the number of results to 2. Usually a limit will be higher than 2.

from pymongo import MongoClient

client = MongoClient("mongodb://127.0.0.1:27017")
db = client.veterinarian

# Clear our collection.
db.animals.delete_many({})

# Insert some animals into a collection.
db.animals.insert_many([
    {"type": "cat", "weight": 15, "color": "orange"},
    {"type": "dog", "weight": 10, "color": "black"},
    {"type": "dog", "weight": 35, "color": "black"},
    {"type": "dog", "weight": 20, "color": "white"}
])

# Find all dogs with limit of 2 results.
cursor = db.animals.find({"type": "dog"}).limit(2)
print("FIND DOG LIMIT 2")
for c in cursor:
    print(c)FIND DOG LIMIT 2
{'type': 'dog', '_id': ObjectId('59ef473525149701747bc4c0'),
 'color': 'black', 'weight': 10}
{'type': 'dog', '_id': ObjectId('59ef473525149701747bc4c1'),
 'color': 'black', 'weight': 35}

Notes, limit

In SQL we combine a "LIMIT" into the query language. But in MongoDB we use direct Python method calls. We use "limit" after the find call.

A review

To create more complex queries in MongoDB we chain method calls after find(). Not just limit() can be used—other methods like sort and skip are available.