spring-guides/gs-accessing-data-mongodb

You will store Customer POJOs (Plain Old Java Objects) in a MongoDB database by using Spring Data MongoDB.

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You can use this pre-initialized project and click Generate to download a ZIP file. This project is configured to fit the examples in this tutorial.

To manually initialize the project:

1. Navigate to https://start.spring.io. This service pulls in all the dependencies you need for an application and does most of the setup for you.

2. Choose either Gradle or Maven and the language you want to use. This guide assumes that you chose Java.

3. Click Dependencies and select Spring Data MongoDB.

4. Click Generate.

5. Download the resulting ZIP file, which is an archive of a web application that is configured with your choices.

With your project set up, you can install and launch the MongoDB database.

If you use a Mac with Homebrew, you can run the following command:

With MacPorts, you can run the following command:

For other systems with package management, such as Redhat, Ubuntu, Debian, CentOS, and Windows, see the instructions at https://docs.mongodb.org/manual/installation/.

After you install MongoDB, you can launch it in a console window by running the following command (which also starts up a server process):

You should see output similar to the following:

MongoDB is a NoSQL document store. In this example, you store Customer objects. The following listing shows the Customer class (in src/main/java/com/example/accessingdatamongodb/Customer.java):

Here you have a Customer class with three attributes: id, firstName, and lastName. The id is mostly for internal use by MongoDB. You also have a single constructor to populate the entities when creating a new instance.

id fits the standard name for a MongoDB ID, so it does not require any special annotation to tag it for Spring Data MongoDB.

The other two properties, firstName and lastName, are left unannotated. It is assumed that they are mapped to fields that share the same name as the properties themselves.

The convenient toString() method prints out the details about a customer.

Spring Data MongoDB focuses on storing data in MongoDB. It also inherits functionality from the Spring Data Commons project, such as the ability to derive queries. Essentially, you need not learn the query language of MongoDB. You can write a handful of methods and the queries are written for you.

To see how this works, create a repository interface that queries Customer documents, as the following listing (in src/main/java/com/example/accessingdatamongodb/CustomerRepository.java) shows:

CustomerRepository extends the MongoRepository interface and plugs in the type of values and ID that it works with: Customer and String, respectively. This interface comes with many operations, including standard CRUD operations (create, read, update, and delete).

You can define other queries by declaring their method signatures. In this case, add findByFirstName, which essentially seeks documents of type Customer and finds the documents that match on firstName.

You also have findByLastName, which finds a list of people by last name.

In a typical Java application, you write a class that implements CustomerRepository and craft the queries yourself. What makes Spring Data MongoDB so useful is the fact that you need not create this implementation. Spring Data MongoDB creates it on the fly when you run the application.

Now you can wire up this application and see what it looks like!

Spring Initializr creates a simple class for the application. The following listing shows the class that Initializr created for this example (in src/main/java/com/example/accessingdatamongodb/AccessingDataMongodbApplication.java):

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Spring Boot automatically handles those repositories as long as they are included in the same package (or a sub-package) of your @SpringBootApplication class. For more control over the registration process, you can use the @EnableMongoRepositories annotation.

Spring Data MongoDB uses the MongoTemplate to execute the queries behind your find* methods. You can use the template yourself for more complex queries, but this guide does not cover that. (see the Spring Data MongoDB Reference Guide)

Now you need to modify the simple class that the Initializr created for you. You need to set up some data and use it to generate output. The following listing shows the finished AccessingDataMongodbApplication class (in src/main/java/com/example/accessingdatamongodb/AccessingDataMongodbApplication.java):

AccessingDataMongodbApplication includes a main() method that autowires an instance of CustomerRepository. Spring Data MongoDB dynamically creates a proxy and injects it there. We use the CustomerRepository through a few tests. First, it saves a handful of Customer objects, demonstrating the save() method and setting up some data to use. Next, it calls findAll() to fetch all Customer objects from the database. Then it calls findByFirstName() to fetch a single Customer by her first name. Finally, it calls findByLastName() to find all customers whose last name is Smith.

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As AccessingDataMongodbApplication implements CommandLineRunner, the run method is automatically invoked when Spring Boot starts. You should see something like the following (with other output, such as queries, as well):

Congratulations! You set up a MongoDB server and wrote a simple application that uses Spring Data MongoDB to save objects to and fetch them from a database, all without writing a concrete repository implementation.

The following guides may also be helpful:

• Accessing MongoDB Data with REST

• Accessing Data with JPA

• Accessing Data with Gemfire

• Accessing data with MySQL

• Accessing Data with Neo4j

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