MongoDB Repository

What is MongoRepository?

An interface called MongoRepository is offered by Spring Data in the org.springframework.data.mongodb.repository package. The CrudRepository interface is further extended by the QueryByExampleExecutor and PagingAndSortingRepository interfaces. Mongodb repository offers all the tools required to build CRUD applications, and it also enables derived custom query methods.

Syntax

Description of the parameters used in the above command :

• T : Type of domain that the repository control (Typically, the name of the Entity/Model class)
• ID : The entity type of the repository's entity id (Typically, the Entity/Model class's wrapper class for your @Id is built there.)

Illustrative Example

public interface BookRepo extends MongoRepository<Book, Integer> {}

This represents the generic type parameters used by the MongoRepository interface. In this case, Book represents the entity class that defines the structure of a book, and Integer represents the type of the book's identifier.

By extending the MongoRepository interface with Book as the entity type and Integer as the identifier type, the BookRepo interface inherits various CRUD operations and additional querying capabilities from the MongoRepository. These operations include saving, updating, deleting, and finding books based on their identifiers or specific criteria.

MongoRepository Configuration

1. XML Configuration : We must carry out the settings from section 3.1 and set up the repositories in order to use custom repositories (extending the Mongodb repository):

   <mongo:repositories base-package="com.baeldung.repository" mongo-template-ref="mongoTemplate"/>

2. Java Configuration : In a similar terms, we'll extend the setup we already developed in section 3.2 and include a fresh annotation:

   @EnableMongoRepositories(basePackages = "com.baeldung.repository")

3. Create the Repository : After setup, we must extend the current Mongodb repository interface to establish a repository:

   public interface UserRepository extends MongoRepository<User, String> { // }

Now that this UserRepository has been automatically wired, we may use Mongodb repository operations or add our own.

How to Use MongoRepository?

Insert

Let's begin with an empty database and the insert operation :

Now let us insert one user in the above database :

User Class :

UserService class :

UserRepository class :

The database will appear as follows :

Save- Insert

The save action has save-or-update semantics, meaning that it either does an update if an id is present or an insert if it is not.

Let's examine the insert, the first semantic, initially database in empty.

Now, when a new user is saved :

The database will appear as follows :

The identical action, save, will then be examined with update semantics.

Save- Update

Now let's examine save with update semantics applied to a preexisting entity :

We will update the existing user when we save it :

The database will appear as follows :

Because we utilise an object with a known _id, we can see that in this specific case, save employs the semantics of update.

Delete

The database was in the following condition before calling delete :

Now we will use the delete operation :

The database will appear as follows :

{}

FindOne

The database is in the following condition when findOne is called :

Now let's run the findOne command :

And the outcome will return the following information :

Exists

Before calling, the database is in the following condition :

Let's execute the existing command, which will naturally return true :

FindAll with Sort

Before using findAll, the database was in this condition :

Now we will use the function findAll with sort :

The outcome will be arranged in a sorted order by name :

FindAll with Pageable

Before using findAll, the database was in this condition :

Let's run findAll now while using a pagination request :

There will be just one person on the resultant users list :

Different Methods

The following list includes some of the most significant methods found inside the JpaRepository.

1. saveAll() : Every specified entity is saved using this method.

   • Syntax : <S extends T> List<S> saveAll(Iterable<S> entities)
   • Parameters : Entities cannot be null, nor can they contain null.
   • Return Type : The stored entities are never going to be empty. The iterable that is returned will be the exact same size as the one that was supplied as an input.
   • Exception Thrown : If one of the specified entities, or all of them, are null, an IllegalArgumentException is thrown.

2. insert() : Inserts the specified entity. Assumes the instance is brand-new so that insertion optimizations can be used. Use the returned instance for subsequent actions as the entity instance may have undergone substantial modification as a result of the save operation.

   • Syntax : <S extends T> S insert(S entity)
   • Parameters : Entities must not be null.
   • Return Type : The saved entity is returned.

3. findAll() : gives back every instance of that type.

   • Syntax : Iterable<T> findAll()
   • Return Type : All the entities are returned.

MongoRepository Implementation

We'll create a Spring Boot application that uses a Mongodb repository to handle a Book instance. The MongoDB database is used to store the data. A RESTful controller is employed.

• Step 1 : Create a spring boot application using the IntelliJ IDEA.

• Step 2 : Include the following dependency in your project.

  • DevTools
  • MongoDB
  • Spring Web
  • Lombok

  Now lets see how the pom.xml file looks after adding the dependencies.

• Step 3 : Create three packages, and then add some classes and interfaces to each of them as shown in the figure below.
  • model
  • repository
  • controller

Endpoint Testing in Postman

1. Endpoint 1 : POST – http://localhost:8989/addBook I am sending a post request with the keys id, bookName, and authorName.

3. Endpoint 2 : GET – http://localhost:8989/findAllBooks Sending a get request with 2 entries : id, bookName, authorName.

5. Endpoint 3 : Delete – http://localhost:8989/findAllBooks Sending a get request with the id.

Last but not least, MongoDB Compass is represented as follows in the graphic below :