MongoDB – How to query a MongoDB Collection (Part I)

By | 23/02/2022

In this post, we will see some query examples to run in a MongoDB database.

We start writing this Docker-compose file to create a docker container with an instance of MongoDB:

[DOCKER-COMPOSE.YML]

version: '3'
services:
  # MongoDB container definition
  dockermongo:
    # name docker image 
    image: mongo
    # username and password Admin definition
    environment:
      - MONGO_INITDB_ROOT_USERNAME=admindb 
      - MONGO_INITDB_ROOT_PASSWORD=pass123 
    # volume definition
    volumes:
      - dbmongo:/data/db
    ports:
      - 27017:27017
volumes:
  dbmongo:
    driver: local



Now, we execute the docker-composer file and then, we will use NoSQLBooster to run queries in the database:




Now, we create a database called TestQuery:


Then, we create a collection called users:


Finally, we will use the service https://json-generator.com/ to generate five random documents, based on this template, to insert in the Users collection:

{
    _id: '{{objectId()}}',
    isActive: '{{bool()}}',
    picture: 'http://placehold.it/32x32',
    age: '{{integer(20, 40)}}',
    name: '{{firstName()}} {{surname()}}',
    gender: '{{gender()}}',
    company: '{{company().toUpperCase()}}',
    email: '{{email()}}',
    phone: '+1 {{phone()}}',
    address: '{{integer(100, 999)}} {{street()}}, {{city()}}, {{state()}}, {{integer(100, 10000)}}',
    registered: '{{date(new Date(2014, 0, 1), new Date(), "YYYY-MM-ddThh:mm:ss Z")}}',
    tags: [
      '{{repeat(7)}}',
      '{{lorem(1, "words")}}'
    ],
    favoriteFruit: function (tags) {
      var fruits = ['apple', 'banana', 'strawberry'];
      return fruits[tags.integer(0, fruits.length - 1)];
    }
}





Now, after we feeded the database, we will run these queries for the Users collection:

COUNT

db.users.count()


SELECT I

// we take all items
db.users.find()


SELECT II

// we take all items with gender equals to 'female'
db.users.find({"gender":"female"})


// we take all items with gender equals to 'male'
db.users.find({"gender":"male"})


WHERE CLAUSE – GREATER THAN

// we take all items with age greater than 33
db.users.find({"age":{$gt:33}})


WHERE CLAUSE – GREATER THAN EQUALS

// we take all items with age greater or equal at 33
db.users.find({"age":{$gte:33}})


WHERE CLAUSE – LESS THAN

// we take all items with age less than 33
db.users.find({"age":{$lt:33}})


WHERE CLAUSE – LESS THAN EQUALS

// we take all items with age less and equal at 33
db.users.find({"age":{$lte:33}})


WHERE CLAUSE – NOT EQUALS

// we take all items with age not equal 33
db.users.find({"age":{$ne:33}})


AND

// we take all items with age not equal 33 and gender = 'male'
db.users.find({$and: [{"age":{$ne:33}}, {"gender":"male"}]})
db.users.find({"age":{$ne:33}, "gender":"male"})


OR

// we take all items with age>33 or gender = 'female'
db.users.find({$or: [{"age":{$gt:33}}, {"gender":"female"}]})


SELECT WITH SPECIFIC FIELDS

// we take all items with gender = 'male' and age>33
db.users.find({$and: [{"gender":"male"}, {"age":{$gt:33}}]})
// we show only _id, name and email
        .project({_id:1, "name":1, "email":1})


LIMIT

// we show only 1 item
db.users.find({"gender":"male"}).limit(1)


SORT

// we sort by name in ascending order
db.users.find({}).sort({"name":1})


// we sort by name in descending order
db.users.find({}).sort({"name":-1})



Leave a Reply

Your email address will not be published.