Spring Data MongoDB

February 16, 2021

Spring Data MongoDB makes it possible to integrate a Spring Boot application with Mongo document database. It provides a MongoRepository containing all the methods used to perform MongoDB CRUD operations.

Before we begin, we will need the following:


  1. JDK installed on your computer.

  2. Your favorite IDE. I’ll be using Intellij IDEA community edition.

  3. Some knowledge of Java and Spring Boot.

  4. MongoDB installed on your computer.

MongoDB terminology

  • Database is a container for collections and can be thought of as a RDBMS database, which is a container for Tables.
  • Collection is equivalent to Tables in RDBMS, but unlike a table, it has a dynamic schema. A collection exists within a database.
  • Document is a single record in a MongoDB collection. It can be thought of as a row in RDBMS.
  • Field this is a document that has zero or more fields. It’s like an RDBMS column having a key-value pair.
  • Embedded document is an efficient and clean way to store related data, especially data that are regularly accessed together.
  • Primary key uniquely identifies a document.

Creating application

We will be using spring initializr to create our application.

  1. Open Spring initializr in your browser.

  2. Select language to Kotlin.

  3. Add Spring Web, Spring Data MongoDB, dependencies.

  4. Leave other configurations as default and click on generate the project.

  5. Unzip the downloaded project and open it in your favorite IDE. I’ll be using Intelij IDEA community, which is available for free.

  6. Sync the project with maven to download all the dependencies.

Domain layer

In the root package of our application, create a package named domain.

Create a Kotlin file named Todo.kt in the domain package we have created above and add the code snippet below into the file.

import org.springframework.data.annotation.Id

import org.springframework.data.mongodb.core.mapping.Document

@Document(collection = "todo")

data class Todo(


   val id: String,

   var title: String,

   var description: String,

   var isCompleted: Boolean

  • @Document(collection = "todo") annotation marks the Todo data class as a MongoDB document that will be stored under the todo collection.

  • @Id marks the id field as a unique object id in the MongoDB collection.

Controller layer

In the root package of our application, create a package named controllers.

Create a Kotlin file named TodoController.kt and add the code snippet below.




class TodoController(val todoService: TodoService) {

   //Get all todos in the database


   fun getAllTodos(): ResponseEntity<List<Todo>> {

       return ResponseEntity(todoService.getTodos(), HttpStatus.OK)


   //Get Todo from the database by id


   fun getTodoById(@PathVariable("id") id: String): ResponseEntity<Todo> {

       return ResponseEntity(todoService.getTodoById(id), HttpStatus.OK)


   //save a todo into the database


   fun saveTodo(@RequestBody todo: Todo): ResponseEntity<Any> {

       return ResponseEntity(todoService.saveTodo(todo), HttpStatus.CREATED)


   //update todo


   fun updateTodo(@RequestBody todo: Todo): ResponseEntity<Any> {

       return ResponseEntity(todoService.updateTodo(todo), HttpStatus.OK)


   //delete todo


   fun deleteTodo(@PathVariable("id") id: String): ResponseEntity<Any> {

       return ResponseEntity(todoService.deleteTodo(id), HttpStatus.NO_CONTENT)


  • @CrossOrigin annotation configures the allowed origins. It is also known as cors, cors allows applications to run on different domains to communicate.

  • @RestController annotation defines a controller and indicates that the return value of the methods should be bound to the web response body.

  • @RequestMapping declares that all APIs URL in the controller will start with /api/v1/todos/.

Repository layer

In the root package of our application create a package named repository and create a Kotlin file named TodoRepository.kt within the repository package, add the code snippet below.

interface TodoRepository : MongoRepository<Todo, String> {

  • interface TodoRepository extends the MongoRepository interface that contains all the CRUD functions that we are going to use to query our MongoDB collection.

Service layer

In the root project package, create a package named service and add two Kotlin files TodoService.kt, TodoServiceImpl with the code snippets below.

interface TodoService {

   fun saveTodo(todo: Todo)

   fun getTodos(): List<Todo>

   fun getTodoById(id: String): Todo

   fun deleteTodo(id: String)

   fun updateTodo(todo: Todo)



class TodoServiceImpl(val todoRepository: TodoRepository) : TodoService {

   override fun saveTodo(todo: Todo) {



   override fun getTodos(): List<Todo> {

       return todoRepository.findAll()


   override fun getTodoById(id: String): Todo {

       val todoQueried: Optional<Todo> = todoRepository.findById(id)

       if (todoQueried.isPresent) {

           return todoQueried.get()

       } else {

           throw IllegalStateException("Todo with id $id not found")



   override fun deleteTodo(id: String) {



   override fun updateTodo(todo: Todo) {

       val todoQueried: Optional<Todo> = todoRepository.findById(todo.id)

       if (todoQueried.isPresent) {

           val _todo = todoQueried.get()

           _todo.description = todo.description

           _todo.isCompleted = todo.isCompleted

           _todo.title = todo.title


       } else {

           throw IllegalStateException("Todo with id ${todo.id} is not found")





Connecting to MongoDB locally In the resources directory, open the application.properties file in your IDE and add the configurations below.


  • spring.data.mongodb.database=todo_db indicates that our database name is todo_db.

  • spring.data.mongodb.port=27017 indicates that we will be connecting to mongodb through port 27017.

Connecting to Mongo Atlas

  1. Visit Mongo Atlas and create an account.

  2. Click on the Database Access side menu and add a database user.

Mongo Atlas database user

  1. Click on the Cluster side menu and create a database.

Mongo Atlas create database

  1. On the Cluster side menu, click on connect and select the connection method as connect your application. Copy the connection string.

Mongo Atlas connection string

  1. Add configurations below to the application.properties file.



  • Change <username>, <password>, and <database> to the credentials you have created in Mongo Atlas.


You have now learned how to create a Spring Boot CRUD API in Kotlin and MongoDB, add fields dateCreated and lastModified in the Todo data class.

You can find the source code here.

Happy coding.

Peer review contribution by: Linus Muema