Advanced ORM with Spring Boot

This repository contains a Spring Boot exercise that demonstrates advanced Object-Relational Mapping (ORM) techniques using Spring Data JPA and Hibernate. Specifically, it focuses on implementing relationships between entities.

Setting Up The Database

The first step in working with this repository and application is to set up the database. Open your mysql workbench and create a new schema called orm-exercise. You do not need to create any tables, or set anything up in the database as Spring Boot JPA will do that for you.

Updating the application.properties file

Next, we need to update the application.properties file to configure the database connection. Open the src/main/resources/application.properties file and modify the following lines to reflect your username and password for the MySQL server:

spring.datasource.username=mikel
spring.datasource.password=z9y6x3

You should also review the other properties in the application.properties file to ensure they are set correctly for your environment. The spring.datasource.url property should point to the orm-exercise schema you created earlier, and the spring.jpa.hibernate.ddl-auto property should be set to update to allow JPA to create and update the database schema as needed test.

Reviewing the Application Code

The application in this repository is a simple JPA/Spring Boot application that employs concepts that you have learned in previous exercises. It includes a single model class, Contact, which represents a contact entity in the database. This class currently has three fields: id, name, and email. It also contains a repository interface, ContactRepository, which extends the JpaRepository interface to provide basic CRUD operations for the Contact entity. Finally, there is a controller class, ContactController, which exposes RESTful endpoints for managing contacts.

Review this code to familiarize yourself with how the application is structured and to be sure that you understand how the existing code works.

Launching the Application and Interacting with the API

Once you have set up the database and updated the application.properties file, you can launch the application. You can do this by running the OrmExerciseApplication class from your IDE.

To interact with and test the API, you will use Postman and MySql Workbench. You should be familiar with how to use these tools from previous exercises.

Once the application launches successfully, you can interact with the API using Postman. You should perform the following operations using Postman:

1. Create a new contact by sending a POST request to http://localhost:8080/contacts with a JSON body containing the name and email fields.

2. Retrieve all contacts by sending a GET request to http://localhost:8080/contacts.

3. Update an existing contact by sending a PUT request to http://localhost:8080/contacts/{id} with a JSON body containing the updated name and email fields.

4. Delete a contact by sending a DELETE request to http://localhost:8080/contacts/{id}.

As you are interacting with the API using Postman, you should verify that the operations are working correctly by viewing the results in the MySQL Workbench by querying the contacts table in the orm-exercise schema.

Be sure that you are comfortable with performing all of these testing and database verification steps before proceeding to the next section, as you will need to repeat them after making code changes to test the new functionality.

Adding Addresses to Contacts

The main objective of this exercise is to extend the existing application to support addresses for contacts. Each contact can have multiple addresses, and each address is associated with a single contact. This is a one-to-many relationship between the Contact and Address entities.

Creating the Address Entity and Establishing Relationships

You will need to create a new Address entity class that has the following fields: id, street, city, state, and zipCode and contact (of type Contact.) The id field should be annotated as the primary key and set to auto-generate its value.

The contact field should be annotated to establish a many-to-one relationship with the Contact entity. It is very important that you also annotate this field with @JsonIgnore to prevent infinite recursion during JSON serialization.

Updating the Contact Entity

Next, you will need to update the Contact entity class to include a new property call addresses that is a List of Address entities. Add getter and setter methods for this property. You will need to annotate this property to establish a one-to-many relationship with the Address entity. Be sure to set the cascade type to CascadeType.ALL to ensure that when a contact is saved, its associated addresses are also saved.

Verifying the new Entity and Relationship

At this point, you should verify that the new Address entity and the relationship between Contact and Address are set up correctly.

1. Clear the database by dropping the orm-exercise schema and recreating it.

2. Relaunch the application to allow JPA to create the necessary tables in the database.

3. Use Postman to create a new contact with multiple addresses by sending a POST request to http://localhost:8080/contacts with a JSON body that includes an array of addresses. For example:

    {
        "name": "John Doe",
        "email": "[email protected]",
        "addresses": [
            {
                "street": "123 Main St",
                "city": "Anytown",
                "state": "CA",
                "zipCode": "12345"
            },
            {
                "street": "456 Oak St",
                "city": "Othertown",
                "state": "TX",
                "zipCode": "67890"
            }
        ]
    }

4. Verify in MySQL Workbench that the contacts and addresses tables have been created correctly and that the addresses are associated with the correct contact.

5. Retrieve the contact using a GET request to http://localhost:8080/contacts/{id} and verify that the addresses are included in the response.

BONUS: Adding New Endpoints for Address Management

Next, you will add two new endpoints to the ContactController class to manage addresses for contacts:

1. A POST endpoint at /contacts/{contactId}/addresses to add a new address for a specific contact.
2. A DELETE endpoint at /contacts/{contactId}/addresses/{addressId} to delete an address for a specific contact.

For each of these, your controller method should first retrieve the contact by its ID, then find the address by its ID (for deletion), add or remove the address from the contact's list of addresses, and finally save the updated contact entity back to the database.

Testing the New Functionality

1. Launch the application again after making the necessary code changes.
2. Test the new functionality using Postman to ensure that you can add, and delete addresses for a contact using the new endpoints.

Conclusion

By completing this exercise, you will have gained hands-on experience with advanced ORM techniques using Spring Data JPA and Hibernate, including establishing one-to-many relationships between entities and managing related data through RESTful endpoints. This knowledge will be valuable for building more complex applications that require robust data management capabilities.