1. Getting Started
2. What you will need
3. Solution
4. Writing the Application
5. Test Resources
6. Testing the Application
7. Running the Application
8. Next Steps
9. Help with the Micronaut Framework
10. License

Access a MongoDB database with Micronaut Data MongoDB

Learn how to access a MongoDB database with Micronaut Data and the MongoDB Sync driver.

Authors: Tim Yates

Micronaut Version: 4.6.3

1. Getting Started

In this guide, we will create a Micronaut application written in Java.

You will use MongoDB for persistence.

2. What you will need

To complete this guide, you will need the following:

Some time on your hands
A decent text editor or IDE (e.g. IntelliJ IDEA)
JDK 21 or greater installed with JAVA_HOME configured appropriately
Docker installed to run MongoDB and to run tests using Testcontainers.

3. Solution

We recommend that you follow the instructions in the next sections and create the application step by step. However, you can go right to the completed example.

Download and unzip the source

4. Writing the Application

Create an application using the Micronaut Command Line Interface or with Micronaut Launch.

mn create-app example.micronaut.micronautguide \
    --features=data-mongodb \
    --build=maven \
    --lang=java \
    --test=junit

If you don’t specify the --build argument, Gradle with the Kotlin DSL is used as the build tool.
If you don’t specify the --lang argument, Java is used as the language.
If you don’t specify the --test argument, JUnit is used for Java and Kotlin, and Spock is used for Groovy.

The previous command creates a Micronaut application with the default package example.micronaut in a directory named micronautguide.

If you use Micronaut Launch, select Micronaut Application as application type and add data-mongodb features.

If you have an existing Micronaut application and want to add the functionality described here, you can view the dependency and configuration changes from the specified features, and apply those changes to your application.

Diff

Setup IntelliJ IDEA to develop Micronaut Applications.

4.1. Dependencies

In this guide, we use the MongoDB Sync driver.

The data-mongodb features adds the following dependencies:

pom.xml

<!-- Add the following to your annotationProcessorPaths element -->
<path>
    <groupId>io.micronaut.data</groupId>
    <artifactId>micronaut-data-document-processor</artifactId>
</path>
<dependency>
    <groupId>io.micronaut.data</groupId>
    <artifactId>micronaut-data-mongodb</artifactId>
    <scope>compile</scope>
</dependency>
<dependency>
    <groupId>org.mongodb</groupId>
    <artifactId>mongodb-driver-sync</artifactId>
    <scope>runtime</scope>
</dependency>

4.2. POJO

Create a Fruit POJO:

src/main/java/example/micronaut/Fruit.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.core.annotation.Nullable;
import io.micronaut.data.annotation.GeneratedValue;
import io.micronaut.data.annotation.Id;
import io.micronaut.data.annotation.MappedEntity;

import jakarta.validation.constraints.NotBlank;

@MappedEntity (1)
public class Fruit {

    @Id (2)
    @GeneratedValue
    private String id;

    @NonNull
    @NotBlank (3)
    private final String name;

    @Nullable
    private String description;

    public Fruit(@NonNull String name, @Nullable String description) {
        this.name = name;
        this.description = description;
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    @NonNull
    public String getName() {
        return name;
    }

    @Nullable
    public String getDescription() {
        return description;
    }

    public void setDescription(@Nullable String description) {
        this.description = description;
    }
}

1	Annotate the class with `@MappedEntity` to map the class to the table defined in the schema.
2	Specifies the ID of an entity
3	Use `jakarta.validation.constraints` Constraints to ensure the data matches your expectations.

4.3. Repository

Create a repository interface to encapsulate the CRUD actions for Fruit.

src/main/java/example/micronaut/FruitRepository.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.data.mongodb.annotation.MongoRepository;
import io.micronaut.data.repository.CrudRepository;

import java.util.List;

@MongoRepository (1)
public interface FruitRepository extends CrudRepository<Fruit, String> {

    @NonNull
    Iterable<Fruit> findByNameInList(@NonNull List<String> names); (2)
}

1	Annotate with `@MongoRepository`.
2	Add a finder for finding fruit by a list of names.

4.4. Service

Create a service FruitService as an API to interact with the Fruit repository. This will allow you to keep business logic out of the controller, and to test the controller later without interacting with a real database.

src/main/java/example/micronaut/FruitService.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;

import java.util.List;
import java.util.Optional;

interface FruitService {

    Iterable<Fruit> list();

    Fruit save(Fruit fruit);

    Optional<Fruit> find(@NonNull String id);

    Iterable<Fruit> findByNameInList(List<String> name);
}

And then create a default implementation of this service.

src/main/java/example/micronaut/DefaultFruitService.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import jakarta.inject.Singleton;

import java.util.List;
import java.util.Optional;

@Singleton (1)
class DefaultFruitService implements FruitService {

    private final FruitRepository fruitRepository;

    public DefaultFruitService(FruitRepository fruitRepository) {
        this.fruitRepository = fruitRepository;
    }

    public Iterable<Fruit> list() {
        return fruitRepository.findAll();
    }

    public Fruit save(Fruit fruit) {
        if (fruit.getId() == null) {
            return fruitRepository.save(fruit);
        } else {
            return fruitRepository.update(fruit);
        }
    }

    public Optional<Fruit> find(@NonNull String id) {
        return fruitRepository.findById(id);
    }

    public Iterable<Fruit> findByNameInList(List<String> name) {
        return fruitRepository.findByNameInList(name);
    }
}

1	Use `jakarta.inject.Singleton` to designate a class as a singleton.

4.5. Controller

Create FruitController:

src/main/java/example/micronaut/FruitController.java

package example.micronaut;

import io.micronaut.core.annotation.NonNull;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.PathVariable;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Put;
import io.micronaut.http.annotation.QueryValue;
import io.micronaut.http.annotation.Status;
import io.micronaut.scheduling.TaskExecutors;
import io.micronaut.scheduling.annotation.ExecuteOn;

import jakarta.validation.Valid;
import jakarta.validation.constraints.NotNull;

import java.util.List;
import java.util.Optional;

@Controller("/fruits") (1)
@ExecuteOn(TaskExecutors.BLOCKING)  (2)
class FruitController {

    private final FruitService fruitService;

    FruitController(FruitService fruitService) {  (3)
        this.fruitService = fruitService;
    }

    @Get  (4)
    Iterable<Fruit> list() {
        return fruitService.list();
    }

    @Post (5)
    @Status(HttpStatus.CREATED) (6)
    Fruit save(@NonNull @NotNull @Valid Fruit fruit) { (7)
        return fruitService.save(fruit);
    }

    @Put
    Fruit update(@NonNull @NotNull @Valid Fruit fruit) {
        return fruitService.save(fruit);
    }

    @Get("/{id}") (8)
    Optional<Fruit> find(@PathVariable String id) {
        return fruitService.find(id);
    }

    @Get("/q") (9)
    Iterable<Fruit> query(@QueryValue @NotNull List<String> names) { (10)
        return fruitService.findByNameInList(names);
    }
}

1	The class is defined as a controller with the @Controller annotation mapped to the path `/fruits`.
2	It is critical that any blocking I/O operations (such as fetching the data from the database) are offloaded to a separate thread pool that does not block the Event loop.
3	Use constructor injection to inject a bean of type `FruitService`.
4	The @Get annotation maps the `list` method to an HTTP GET request on `/fruits`.
5	The @Post annotation maps the `save` method to an HTTP POST request on `/fruits`.
6	You can specify the HTTP status code via the `@Status` annotation.
7	Add `@Valid` to any method parameter which requires validation.
8	The @Get annotation maps the `find` method to an HTTP GET request on `/fruits/{id}`.
9	The @Get annotation maps the `findByNameInList` method to an HTTP GET request on `/fruits/q`.
10	Bind a list of Strings to the query parameter `names`

4.6. Test Client

Add a Micronaut declarative HTTP Client to src/test to ease the testing of the application’s API.

src/test/java/example/micronaut/FruitClient.java

package example.micronaut;

import io.micronaut.http.HttpResponse;
import io.micronaut.http.annotation.Get;
import io.micronaut.http.annotation.PathVariable;
import io.micronaut.http.annotation.Post;
import io.micronaut.http.annotation.Put;
import io.micronaut.http.annotation.QueryValue;
import io.micronaut.http.client.annotation.Client;

import jakarta.validation.constraints.NotNull;
import java.util.List;
import java.util.Optional;

@Client("/fruits")
interface FruitClient {

    @Get
    Iterable<Fruit> list();

    @Get("/{id}")
    Optional<Fruit> find(@PathVariable String id);

    @Get("/q")
    Iterable<Fruit> query(@QueryValue @NotNull List<String> names);

    @Post
    HttpResponse<Fruit> save(Fruit fruit);

    @Put
    Fruit update(Fruit fruit);
}

Then create a test that verifies the validation of the Fruit POJO when we create a new entity via POST:

src/test/java/example/micronaut/FruitValidationControllerTest.java

package example.micronaut;

import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.http.client.exceptions.HttpClientResponseException;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;

@MicronautTest
class FruitValidationControllerTest {

    @Inject
    @Client("/")
    HttpClient httpClient;

    @Test
    void fruitIsValidated() {
        HttpClientResponseException exception = assertThrows(
                HttpClientResponseException.class,
                () -> httpClient.toBlocking().exchange(HttpRequest.POST("/fruits", new Fruit("", "")))
        );

        assertEquals(HttpStatus.BAD_REQUEST, exception.getStatus());
    }
}

Create a test that checks our controller works against a real MongoDB database:

src/test/java/example/micronaut/FruitControllerTest.java

package example.micronaut;

import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import org.junit.jupiter.api.Test;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertTrue;

@MicronautTest
class FruitControllerTest {

    @Inject
    FruitClient fruitClient;

    @Test
    void emptyDatabaseContainsNoFruit() {
        assertEquals(0, StreamSupport.stream(fruitClient.list().spliterator(), false).count());
    }

    @Test
    void testInteractionWithTheController() {
        HttpResponse<Fruit> response = fruitClient.save(new Fruit("banana", null));
        assertEquals(HttpStatus.CREATED, response.getStatus());
        Fruit banana = response.getBody().get();

        Iterable<Fruit> fruits = fruitClient.list();

        List<Fruit> fruitList = StreamSupport.stream(fruits.spliterator(), false).collect(Collectors.toList());
        assertEquals(1, fruitList.size());
        assertEquals(banana.getName(), fruitList.get(0).getName());
        assertNull(fruitList.get(0).getDescription());

        response = fruitClient.save(new Fruit("apple", "Keeps the doctor away"));
        assertEquals(HttpStatus.CREATED, response.getStatus());

        fruits = fruitClient.list();
        assertTrue(StreamSupport.stream(fruits.spliterator(), false)
                .anyMatch(f -> "Keeps the doctor away".equals(f.getDescription())));

        banana.setDescription("Yellow and curved");
        fruitClient.update(banana);

        fruits = fruitClient.list();

        assertEquals(
                Stream.of("Keeps the doctor away", "Yellow and curved").collect(Collectors.toSet()),
                StreamSupport.stream(fruits.spliterator(), false)
                        .map(Fruit::getDescription)
                        .collect(Collectors.toSet())
        );
    }

    @Test
    void testSearchWorksAsExpected() {
        fruitClient.save(new Fruit("apple", "Keeps the doctor away"));
        fruitClient.save(new Fruit("pineapple", "Delicious"));
        fruitClient.save(new Fruit("lemon", "Lemonentary my dear Dr Watson"));

        Iterable<Fruit> fruit = fruitClient.query(Arrays.asList("apple", "pineapple"));

        assertTrue(StreamSupport.stream(fruit.spliterator(), false)
                .allMatch(f -> f.getName().equals("apple") || f.getName().equals("pineapple")));
    }
}

And finally, create a test which uses a replacement FruitService to test the controller without touching the database:

src/test/java/example/micronaut/ControllerIsolationTest.java

package example.micronaut;

import io.micronaut.context.annotation.Property;
import io.micronaut.context.annotation.Replaces;
import io.micronaut.context.annotation.Requires;
import io.micronaut.core.type.Argument;
import io.micronaut.http.HttpHeaders;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.HttpResponse;
import io.micronaut.http.HttpStatus;
import io.micronaut.http.MediaType;
import io.micronaut.http.MutableHttpRequest;
import io.micronaut.http.client.HttpClient;
import io.micronaut.http.client.annotation.Client;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import jakarta.inject.Inject;
import jakarta.inject.Singleton;
import org.junit.jupiter.api.Test;

import jakarta.validation.constraints.NotNull;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

@MicronautTest
@Property(name = "spec.name", value = "controller-isolation")
public class ControllerIsolationTest {

    @Inject
    @Client("/")
    HttpClient httpClient;

    @Test
    void checkSerialization() {
        MutableHttpRequest<Object> get = HttpRequest.GET("/fruits");
        HttpResponse<List<Fruit>> response = httpClient.toBlocking().exchange(get, Argument.listOf(Fruit.class));

        assertEquals(HttpStatus.OK, response.getStatus());
        assertEquals(MediaType.APPLICATION_JSON, response.getHeaders().get(HttpHeaders.CONTENT_TYPE));
        assertTrue(response.getBody().isPresent());

        String all = response.getBody().get().stream().map(f -> f.getName() + ":" + f.getDescription()).collect(Collectors.joining(","));
        assertEquals("apple:red,banana:yellow", all);
    }

    @Singleton
    @Replaces(DefaultFruitService.class)
    @Requires(property = "spec.name", value = "controller-isolation")
    static class MockService implements FruitService {

        @Override
        public Iterable<Fruit> list() {
            return Arrays.asList(
                    new Fruit("apple", "red"),
                    new Fruit("banana", "yellow")
            );
        }

        @Override
        public Fruit save(Fruit fruit) {
            return fruit;
        }

        @Override
        public Optional<Fruit> find(@NotNull String id) {
            return Optional.empty();
        }

        @Override
        public Iterable<Fruit> findByNameInList(List<String> name) {
            return Collections.emptyList();
        }
    }
}

5. Test Resources

When the application is started locally — either under test or by running the application — resolution of the property mongodb.uri is detected and the Test Resources service will start a local MongoDB docker container, and inject the properties required to use this as the datasource.

When running under production, you should replace this property with the location of your production MongoDB instance via an environment variable.

MONGODB_URI=mongodb://username:password@production-server:27017/databaseName

For more information, see the MongoDB section of the Test Resources documentation.

6. Testing the Application

To run the tests:

./mvnw test

7. Running the Application

To run the application, use the ./mvnw mn:run command, which starts the application on port 8080.

curl -d '{"name":"Pear"}' \
     -H "Content-Type: application/json" \
     -X POST http://localhost:8080/fruits

curl -i localhost:8080/fruits

HTTP/1.1 200 OK
date: Wed, 15 Sep 2021 12:40:15 GMT
Content-Type: application/json
content-length: 110
connection: keep-alive

[{"name":"Pear"}]

8. Next Steps

Explore more features with Micronaut Guides.

9. Help with the Micronaut Framework

The Micronaut Foundation sponsored the creation of this Guide. A variety of consulting and support services are available.

10. License

All guides are released with an Apache license 2.0 license for the code and a Creative Commons Attribution 4.0 license for the writing and media (images…).

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