MongoDb

Table of contents

Basic:-

Show DB:-

Below commands returns all database in the server

show dbs

To show collection:-

Make sure you’re inside a db and use the following command to get the all the collection names

show collections

Create DB:-

use <database name>

Example:

use shopDB

The above command creates a database if it isn’t already there and the console switches to the db specified

Delete Db

db.dropDatabase();

Make sure you’re currently inside the db you want to delete

Create collection:-

Collection can be created in 2 ways

insertOne

db.<collection name>.insertOne({_id: <id #>, name: “<name>”})

Example:

db.products.insertOne({ _id: 1, name: "Pensil" });

You can also create a collection with multiple documents at once as shown below

Example:

db.products.insertMany([
  { _id: 1, name: "Pensil" },
  { _id: 2, name: "Eraser" },
]);

createCollection

db.createCollection(“<collection name>“)

Example:

db.createCollection("Products");

To read collection:-

There are 2 methods to find a document in a MongoDB collection, find() and findOne().

find

db.<collection name>.find(query,projection)

Here query is the document you want to find and projection determines the visiblity of data within the document

Example:

db.products.find(); //Displays all document in collection
db.products.fund({ name: "Pensil" }); //Displays all documents that match the field's value
db.products.find({ price: { $gt: 1 } }); //Displays all documumt whose price is greater than 1
db.products.find({ _id: 1 }, { name: 1, _id: 0 }); //1st param matches the record, and in 2nd param, 1 means show and 0 don't show

findOne

db.<collection name>.findOne()

To select only one document, we can use the findOne() method. This method also take two arguments as find method above

Insert document in collection

There are 2 methods to insert documents into a collection.

insertOne

db.<collection name>.insertOne()

Example:

db.posts.insertOne({
  title: "Post Title 1",
  body: "Body of post.",
  category: "News",
  likes: 1,
  tags: ["news", "events"],
  date: Date(),
});

insertMany

db.<collection name>.insertMany()

Example:

db.posts.insertMany([
  {
    title: "Post Title 2",
    body: "Body of post.",
    category: "Event",
    likes: 2,
    tags: ["news", "events"],
    date: Date(),
  },
  {
    title: "Post Title 3",
    body: "Body of post.",
    category: "Technology",
    likes: 3,
    tags: ["news", "events"],
    date: Date(),
  },
]);

Update document in collection:-

To update an existing document we can use the updateOne() or updateMany() methods. The first parameter is a query object to define which document or documents should be updated. The second parameter is an object defining the updated data.

updateOne

db.<collection name>.updateOne({_id: <id #>},{$set:{<field>:<value>}})

Example:

db.products.updateOne({ _id: 1 }, { $set: { stock: 32 } });

updateMany

db.<collection name>.updateMany()

db.posts.updateMany({}, { $inc: { likes: 1 } }); //Update likes on all documents by 1.

Delete record:-

We can delete documents by using the methods deleteOne() or deleteMany(). These methods accept a query object. The matching documents will be deleted.

deleteOne

db.<collection name>.deleteOne({_id: <id #>})

Example:

db.products.deleteOne({ _id: 1 });

deleteMany

db.<collection name>.deleteMany() The deleteMany() method will delete all documents that match the query provided.