Database, IT Technology

Mastering Python MongoDB Queries: Comprehensive Examples and Solutions

Posted on by Thao Nguyen

MongoDB is a cross-platform, document-oriented, non-relational (i.e., NoSQL) database program. It is an open-source document database that stores data in the form of key-value pairs.

What is a MongoDB query?

MongoDB queries are used to specify selection filters via query operators while retrieving data from a collection via the db.find() method. We can easily filter documents using query objects. To apply a filter to a collection, we can pass a query specifying the desired document condition as a parameter to this method, which is an optional parameter to the db.find() method.

Query selector:

The following is a list of some of the operators used in MongoDB queries.

operategrammardescription
equal{“key” : “value”}Matches a value equal to the specified value.
Less than{“key” :{$lt:”value”}}Matches a value that is less than the specified value.
Greater than{“key” :{$gt:”value”}}Matches a value that is greater than the specified value.
Less than or equal to{“key” :{$lte:”value”}}Matches values that are less than or equal to the specified value.
Greater than or equal to{“key” :{$lte:”value”}}Matches values that are greater than or equal to the specified value.
Not equal{“key”:{$ne: “value”}}Matches all values that are not equal to the specified value.
Logic with{ “$and”:[{exp1}, {exp2}, …, {expN}] }The query clause is connected with logical AND, which returns all documents that match the conditions of both clauses.
Logic or{ “$or”:[{exp1}, {Concatenating the query clauses with a logical OR will return all documents that match the conditions of either clause.
Logical non{ “$not”:[{exp1}, {exp2}, …, {expN}] }Reverses the effect of the query expression and returns documents that don’t match the query expression.

The database or collection on which we run:

Example 1:

# importing Mongoclient from pymongo
from pymongo import MongoClient 
  
  
# Making Connection
myclient = MongoClient( "mongodb://localhost:27017/" ) 
   
# database 
db = myclient[ "mydatabase" ]
   
# Created or Switched to collection
# names: lsbin
Collection = db[ "lsbin" ]
  
# Filtering the Quantities greater
# than 40 using query.
cursor = Collection.find({ "Quantity" :{ "$gt" : 40 }})
  
# Printing the filterd data.
print ( "The data having Quantity greater than 40 is:" )
for record in cursor: 
     print (record) 
      
# Filtering the Quantities less 
# than 40 using query.
cursor = Collection.find({ "Quantity" :{ "$lt" : 40 }})
  
# Printing the filterd data.
print ( "\nThe data having Quantity less than 40 is:" )
for record in cursor: 
     print (record)

The output is as follows:

Example 2:

# importing Mongoclient from pymongo
from pymongo import MongoClient 
  
  
# Making Connection
myclient = MongoClient( "mongodb://localhost:27017/" ) 
   
# database 
db = myclient[ "mydatabase" ]
   
# Created or Switched to collection 
# names: lsbin
Collection = db[ "lsbin" ]
  
# Filtering the (Quantities greater than
# 40 AND greater than 40) using AND query.
cursor = Collection.find({ "$and" :[{ "Quantity" :{ "$gt" : 40 }}, { "Quantity" :{ "$gt" : 50 }}]})
  
# Printing the filterd data.
print ("Quantities greater than 40 AND\
Quantities greater than 40 :")
for record in cursor: 
     print (record) 
  
# Filtering the (Quantities greater than
# 40 OR greater than 40) using OR query.
cursor = Collection.find({ "$or" :[{ "Quantity" :{ "$gt" : 40 }}, { "Quantity" :{ "$gt" : 50 }}]})
  
# Printing the filterd data.
print ()
print ("Quantities greater than 40 OR\
Quantities greater than 40 :")
for record in cursor: 
     print (record)

The output is as follows:

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Thao Nguyen