CRUD operations in MongoDB Shell

Introduction

Assuming that the database is already created in the mongoDB shell. We can perform CRUD operations like create, read, update, and delete documents. A document is basically a record in MongoDB.  It is a data structure composed of field and value pairs. MongoDB documents are similar to JSON objects. The values of fields may include other documents, arrays, and arrays of documents.

Prerequisites

• Install mongodb-community
  • Refer to the blog Create database in MongoDB for installing using brew and connect to the MongoDB Shell

Create database command

Execute the following command to create a database with name sample_db

> use sample_db

CRUD Operations

Insert a single Document

To insert a single document in the collection, execute db.collection.insertOne() Note: If the -id field is not specifies then MongoDb adds the id field with ObjectId value to the document inserted.

db.users.insertOne({first-name: "Anchal", last-name:"Gupta", age: 24})

Insert Multiple Documents

We can insert multiple documents in the collection by using db.collection.insertMany() command.

db.departments.insertMany([
{
name: "sales",
people: 10,
},
{
name: "backend",
people: 15,
},
]);

Read All Documents in a Collection

To read all the documents (data) in a collection, execute db.collection.find()

It will return all the documents inside a collection.

Read documents by specifying field and value

To read any specific document, we can specify the field and value with the command db.document.find({"field": "value"})

It will return the documents that match the specifications.

We can also specify query filters and add more specifications

Example: The following query will return upto 5 users of age greater than 18.

db.users.find(
{age: {$gt: 18} }
).limit(5)

Update single document

Update commands are used to modify the existing documents in a collection.

To update a document in the collection, execute db.collection.updateOne() along with the update operators such as $set to modify field values.

db.departments.updateOne(
{
name:"sales",
},
{
$set: {
people:20,
}
})

The first document where name equals sales will be updated.

Update multiple document

To update multiple document, execute the command db.departments.updateMany() .

db.departments.updateMany(
{people: {$gt:10},
{
$set:{location:"tokyo"},
})

It will update all the documents where people are greater than 10

Replace a document

To replace entire content of the document expect the _id field, pass the new document as the second argument and execute the command db.departments.replaceOne() .

While executing the replace command, do not include the update operators expression.

db.departments.replaceOne(
{name:"sales"},
{name:"design", people:8}
)

It will replace the document where name is equal to the sales with the new document {name:"design", people:8} passed as the second arguement

Delete one document

To delete a document from the collection, execute the command db.collection.deleteOne() .

db.departments.deleteOne({name:"design"})

It will delete the first document where the name is equal to design

Delete documents that match the condition

To delete multiple documents from the collection, execute the command db.collection.deleteMany() .

db.departments.deleteMany({location:"tokyo"})

It will delete all the documents from the collection where location is equal to tokyo

Delete all documents

To delete all the documents from the collection, execute the command db.departments.deleteMany({})

Conclusion

I tried executing the MongoDB crud operations (create, read, update, delete) using the MongoDB shell. CRUD operations describe the conventions of a user-interface that let users view, search, and modify parts of the database.

References

• https://www.mongodb.com/docs/manual/crud/
• https://www.mongodb.com/basics/crud